Main Street Capital CORP

Notes to the Consolidated Financial Statements

NOTE A —ORGANIZATION AND BASIS OF PRESENTATION

1. Organization

Main Street Capital Corporation (“MSCC” or, together with its consolidated subsidiaries, “Main Street” or the “Company”) is a principal investment firm primarily focused on providing customized long-term debt and equity capital solutions to lower middle market (“LMM”) companies (its “LMM investment strategy”) and debt capital to private (“Private Loan”) companies owned by or in the process of being acquired by a private equity fund (its “Private Loan investment strategy”). Main Street’s portfolio investments are typically made to support management buyouts, recapitalizations, growth financings, refinancings and acquisitions of companies that operate in diverse industry sectors. Main Street seeks to partner with entrepreneurs, business owners and management teams and generally provides “one-stop” debt and equity financing solutions within its LMM investment strategy. Main Street invests primarily in secured debt investments, equity investments, warrants and other securities of LMM companies typically based in the United States. Main Street also seeks to partner with private equity fund sponsors in its Private Loan investment strategy and primarily invests in secured debt investments of Private Loan companies generally headquartered in the United States.

Main Street also maintains a legacy portfolio of investments in larger middle market (“Middle Market”) companies (its “Middle Market investment portfolio”) and a limited portfolio of other portfolio (“Other Portfolio”) investments. Main Street’s Middle Market investments are generally debt investments in companies owned by a private equity fund that were originally issued through a syndication financing process. Main Street has generally stopped making new Middle Market investments and expects the size of its Middle Market investment portfolio to continue to decline in future periods as its existing Middle Market investments are repaid or sold. Main Street’s Other Portfolio investments primarily consist of investments that are not consistent with the typical profiles for its LMM, Private Loan or Middle Market portfolio investments, including investments in unaffiliated investment companies and private funds managed by third parties.

The “Investment Portfolio,” as used herein, refers to all of Main Street’s investments in LMM portfolio companies, investments in Private Loan portfolio companies, investments in Middle Market portfolio companies, Other Portfolio investments, short-term portfolio investments (as discussed in Note C — Fair Value Hierarchy for Investments — Portfolio Composition — Investment Portfolio Composition) and the investment in the External Investment Manager (as defined below).

MSCC was formed in March 2007 to operate as an internally managed business development company (“BDC”) under the Investment Company Act of 1940, as amended (the “1940 Act”). Because MSCC is internally managed, all of the executive officers and other employees are employed by MSCC. Therefore, MSCC does not pay any external investment advisory fees, but instead directly incurs the operating costs associated with employing investment and portfolio management professionals.

MSCC wholly owns several investment funds, including Main Street Mezzanine Fund, LP (“MSMF”) and Main Street Capital III, LP (“MSC III” and, together with MSMF, the “Funds”), and each of their general partners. The Funds are each licensed as a Small Business Investment Company (“SBIC”) by the United States Small Business Administration (“SBA”).

MSC Adviser I, LLC (the “External Investment Manager”) was formed in November 2013 as a wholly-owned subsidiary of Main Street to provide investment management and other services to parties other than Main Street (“External Parties”) and earns fee income for such services. MSCC has been granted no-action relief by the Securities and Exchange Commission (“SEC”) to allow the External Investment Manager to register as a registered investment adviser under the Investment Advisers Act of 1940, as amended. Since the External Investment Manager conducts all of its investment management activities for External Parties, it is accounted for as a portfolio investment of Main Street and is not included as a consolidated subsidiary in Main Street’s consolidated financial statements.

MSCC has elected to be treated for U.S. federal income tax purposes as a regulated investment company (“RIC”) under Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”). As a result, MSCC generally does not pay corporate-level U.S. federal income taxes on any net ordinary taxable income or capital gains that it distributes to its stockholders.

MSCC has certain direct and indirect wholly-owned subsidiaries that have elected to be taxable entities (the “Taxable Subsidiaries”). The primary purpose of the Taxable Subsidiaries is to permit MSCC to hold equity investments in portfolio companies which are “pass-through” entities for tax purposes. MSCC also has certain direct and indirect wholly-owned subsidiaries formed for financing purposes (the “Structured Subsidiaries”).

Unless otherwise noted or the context otherwise indicates, the terms the “Company” and “Main Street” refer to MSCC and its consolidated subsidiaries, which include the Funds, the Taxable Subsidiaries and the Structured Subsidiaries.

2. Basis of Presentation

Main Street’s consolidated financial statements are prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). The Company is an investment company following accounting and reporting guidance in Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 946, Financial Services—Investment Companies (“ASC 946”). For each of the periods presented herein, Main Street’s consolidated financial statements include the accounts of MSCC and its consolidated subsidiaries. Main Street’s results of operations for the three and nine months ended September 30, 2025 and 2024, cash flows for the nine months ended September 30, 2025 and 2024 and financial position as of September 30, 2025 and December 31, 2024 are presented on a consolidated basis. The effects of all intercompany transactions between MSCC and its consolidated subsidiaries have been eliminated in consolidation.

The accompanying unaudited consolidated financial statements of Main Street are presented in conformity with U.S. GAAP for interim financial information and pursuant to the requirements for reporting on Form 10-Q and Articles 6, 10 and 12 of Regulation S-X. Accordingly, certain disclosures accompanying annual consolidated financial statements prepared in accordance with U.S. GAAP are omitted. The unaudited consolidated financial statements and notes should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2024. In the opinion of management, the unaudited consolidated financial results included herein contain all adjustments, consisting solely of normal recurring accruals, considered necessary for the fair presentation of financial statements for the interim periods included herein. The results of operations for the three and nine months ended September 30, 2025 are not necessarily indicative of the operating results to be expected for the full year. Financial statements prepared on a U.S. GAAP basis require management to make estimates and assumptions that affect the amounts and disclosures reported in the consolidated financial statements and accompanying notes. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein.

Principles of Consolidation

Under ASC 946, Main Street is precluded from consolidating other entities in which Main Street has equity investments, including those in which it has a controlling interest, unless the other entity is another investment company. An exception to this general principle in ASC 946 occurs if Main Street holds a controlling interest in an operating company that provides all or substantially all of its services directly to Main Street. Accordingly, as noted above, Main Street’s consolidated financial statements include the financial position and operating results for the Funds, the Taxable Subsidiaries and the Structured Subsidiaries. Main Street has determined that none of its portfolio investments qualify for this exception, including the investment in the External Investment Manager. Therefore, Main Street’s Investment Portfolio is carried on the Consolidated Balance Sheets at fair value, as discussed further in Note B.1. — Summary of Significant Accounting Policies — Valuation of the Investment Portfolio, with any adjustments to fair value recognized as “Net Unrealized Appreciation (Depreciation)” until the investment is realized, usually upon exit, resulting in any gain or loss being recognized as a “Net Realized Gain (Loss),” in both cases on the Consolidated Statements of Operations.

Portfolio Investment Classification

Main Street classifies its Investment Portfolio in accordance with the requirements of the 1940 Act. Under the 1940 Act, (a) “Control” investments are defined as investments in which Main Street owns more than 25% of the voting securities or has rights to maintain greater than 50% of the board representation, (b) “Affiliate” investments are defined as investments in which Main Street owns between 5% and 25% (inclusive) of the voting securities and does not have rights to maintain greater than 50% of the board representation and (c) “Non-Control/Non-Affiliate” investments are defined as investments that are neither Control investments nor Affiliate investments. For purposes of determining the classification of its Investment Portfolio, Main Street has excluded consideration of any voting securities or board appointment rights held by third-party investment funds advised by the External Investment Manager.

3. Revisions to the Presentation of Previously Issued Financial Statements

As of June 30, 2025, Main Street changed its tax presentation on the Consolidated Statement of Operations to voluntarily correct an immaterial error in order to comply with the applicable presentation requirements in 210.6-07 of Regulation S-X. Net investment income now includes excise tax expense and net investment income related federal and state income and other tax expenses. These revisions had no impact on net increase in net assets resulting from operations or net increase in net assets resulting from operations per share. All prior period net investment income and net investment income per share amounts presented in these consolidated financial statements and the notes thereto have been retrospectively adjusted to conform to the current presentation. The impact of the adjustments on the Consolidated Statement of Operations for the three and nine months ended September 30, 2024 is as follows:

The adjustments also impacted the ratio of net investment income to average net asset value (“NAV”) as presented in Note F— Financial Highlights.

NOTE B —SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

1. Valuation of the Investment Portfolio

Main Street accounts for its Investment Portfolio at fair value. As a result, Main Street follows the provisions of ASC 820, Fair Value Measurements and Disclosures (“ASC 820”). ASC 820 defines fair value, establishes a framework for measuring fair value, establishes a fair value hierarchy based on the quality of inputs used to measure fair value and enhances disclosure requirements for fair value measurements. ASC 820 requires Main Street to assume that the portfolio investment is to be sold in the principal market to independent market participants, which may be a hypothetical market. Market participants are defined as buyers and sellers in the principal market that are independent, knowledgeable and willing and able to transact.

Main Street’s portfolio strategy calls for it to invest primarily in illiquid debt and equity securities issued by LMM companies and debt securities issued by Private Loan companies. Main Street also maintains a legacy portfolio of investments in Middle Market companies and a limited portfolio of Other Portfolio investments. Main Street’s portfolio may also periodically include short-term portfolio investments that are atypical of Main Street’s LMM and Private Loan portfolio investments as they are intended to be a short-term deployment of capital and are more liquid than investments within the LMM and Private Loan investment portfolios. Main Street’s portfolio investments may be subject to restrictions on resale.

LMM investments and Other Portfolio investments generally have no established trading market, while Private Loan investments may include investments which have no established market or have established markets that are not active. Middle Market and short-term portfolio investments generally have established markets that are not active. Main Street determines in good faith the fair value of its Investment Portfolio pursuant to a valuation policy in accordance with ASC 820, with such valuation process approved by its Board of Directors and in accordance with the 1940 Act. Main Street’s valuation policies and processes are intended to provide a consistent basis for determining the fair value of Main Street’s Investment Portfolio.

For LMM portfolio investments, Main Street generally reviews external events, including private mergers, sales and acquisitions involving comparable companies, and includes these events in the valuation process by using an enterprise value waterfall methodology (“Waterfall”) for its LMM equity investments and an income approach using a yield-to-maturity model (“Yield-to-Maturity”) valuation method for its LMM debt investments. For Private Loan and Middle Market portfolio investments in debt securities for which it has determined that third-party quotes or other independent pricing are not available or appropriate, Main Street generally estimates the fair value based on the assumptions that it believes hypothetical market participants would use to value the investment in a current hypothetical sale using the Yield-to-Maturity valuation method. For Middle Market and short-term portfolio investments in debt securities for which it has determined that third-party quotes or other independent prices are available, Main Street primarily uses quoted prices in the valuation process. Main Street determines the appropriateness of the use of third-party broker quotes, if any, in determining fair value based on its understanding of the level of actual transactions used by the broker to develop the quote and whether the quote was an indicative price or binding offer, the depth and consistency of broker quotes and the correlation of changes in broker quotes with underlying performance of the portfolio company and other market indices. For its Other Portfolio equity investments, Main Street generally calculates the fair value of the investment primarily based on the NAV of the fund and adjusts the fair value for other factors deemed relevant that would affect the fair value of the investment. All of the valuation approaches for Main Street’s portfolio investments estimate the value of the investment as if Main Street were to sell, or exit, the investment as of the measurement date.

These valuation approaches consider the value associated with Main Street’s ability to control the capital structure of the portfolio company, as well as the timing of a potential exit. For valuation purposes, “control” portfolio investments are composed of debt and equity securities in companies for which Main Street has a controlling interest in the equity ownership of the portfolio company or the ability to nominate a majority of the portfolio company’s board of directors. For valuation purposes, “non-control” portfolio investments are generally composed of debt and equity securities in companies for which Main Street does not have a controlling interest in the equity ownership of the portfolio company or the ability to nominate a majority of the portfolio company’s board of directors.

Under the Waterfall valuation method, Main Street estimates the enterprise value of a portfolio company using a combination of market and income approaches or other appropriate valuation methods, such as considering recent transactions in the equity securities of the portfolio company or third-party valuations of the portfolio company, and then performs a Waterfall calculation by allocating the enterprise value over the portfolio company’s securities in order of their preference relative to one another. The enterprise value is the fair value at which an enterprise could be sold in a transaction between two willing parties, other than through a forced or liquidation sale. Typically, privately held companies are bought and sold based on multiples of earnings before interest, taxes, depreciation and amortization (“EBITDA”), cash flows, net income, revenues, or in limited cases, book value. There is no single methodology for estimating enterprise value. For any one portfolio company, enterprise value is generally described as a range of values from which a single estimate of enterprise value is derived. In estimating the enterprise value of a portfolio company, Main Street analyzes various factors including the portfolio company’s historical and projected financial results. Due to SEC deadlines for Main Street’s quarterly and annual financial reporting, the operating results of a portfolio company used in the current period valuation are generally the results from the period ended three months prior to such valuation date and may include unaudited, projected, budgeted or pro forma financial information and may require adjustments for non-recurring items or to normalize the operating results that may require significant judgment in determining. In addition, projecting future financial results requires significant judgment regarding future growth assumptions. In evaluating the operating results, Main Street also analyzes the impact of exposure to litigation, loss of customers or other contingencies. After determining the appropriate enterprise value, Main Street allocates the enterprise value to investments in order of the legal priority of the various components of the portfolio company’s capital structure. In applying the Waterfall valuation method, Main Street assumes the loans are paid-off at the principal amount in a change in control transaction and are not assumed by the buyer, which Main Street believes is consistent with its past transaction history and standard industry practices.

Under the Yield-to-Maturity valuation method, Main Street also uses the income approach to determine the fair value of debt securities based on projections of the discounted future free cash flows that the debt security will likely generate, including analyzing the discounted cash flows of interest and principal amounts for the debt security, as set forth in the associated loan agreements, as well as the financial position and credit risk of the portfolio company. Main Street’s estimate of the expected repayment date of its debt securities is generally the maturity date of the instrument, as Main Street generally intends to hold its loans and debt securities to maturity. The Yield-to-Maturity analysis also considers changes in leverage levels, credit quality, portfolio company performance, changes in market-based interest rates and other factors. Main Street will generally use the value determined by the Yield-to-Maturity analysis as the fair value for that security; however, because of Main Street’s general intent to hold its loans to maturity, the fair value will not exceed the principal amount of the debt security valued using the Yield-to-Maturity valuation method. A change in the assumptions that Main Street uses to estimate the fair value of its debt securities using the Yield-to-Maturity valuation method could have a material impact on the determination of fair value. If there is deterioration in credit quality or if a debt security is in workout status, Main Street may consider other factors in determining the fair value of the debt security, including the value attributable to the debt security from the enterprise value of the portfolio company or the proceeds that would most likely be received in a liquidation analysis.

Under the NAV valuation method, for an investment in an investment fund that does not have a readily determinable fair value, Main Street measures the fair value of the investment predominately based on the NAV of the investment fund as of the measurement date and adjusts the investment’s fair value for factors known to Main Street that would affect that fund’s NAV, including, but not limited to, fair values for individual investments held by the fund if Main Street holds the same investment or for a publicly traded investment. In addition, in determining the fair value of the investment, Main Street considers whether adjustments to the NAV are necessary in certain circumstances, based on the analysis of any restrictions on redemption of Main Street’s investment as of the measurement date, recent actual sales or redemptions of interests in the investment fund, and expected future cash flows available to equity holders, including the rate of return on those cash flows compared to an implied market return on equity required by market participants, or other uncertainties surrounding Main Street’s ability to realize the full NAV of its interests in the investment fund.

Pursuant to its internal valuation process and the requirements under the 1940 Act, Main Street performs valuation procedures on each of its portfolio investments quarterly. In addition to its internal valuation process, in arriving at estimates of fair value for its investments in its LMM portfolio companies, Main Street, among other things, consults with a nationally recognized independent financial advisory services firm (the “Financial Advisory Firm”). The Financial Advisory Firm analyzes and provides observations, recommendations and an assurance certification regarding Main Street’s determinations of the fair value of its LMM portfolio company investments. The Financial Advisory Firm is generally consulted relative to Main Street’s investments in each LMM portfolio company at least once every calendar year, and for Main Street’s investments in new LMM portfolio companies, at least once in thetwelve-month period subsequent to the initial investment. In certain instances, Main Street may determine that it is not cost-effective, and as a result is not in its stockholders’ best interest, to consult with the Financial Advisory Firm on its investments in one or more LMM portfolio companies. Such instances include, but are not limited to, situations where the fair value of Main Street’s investment in a LMM portfolio company is determined to be insignificant relative to the total Investment Portfolio. Main Street consulted with and received an assurance certification from the Financial Advisory Firm in arriving at its determination of fair value for its investments in a total of 18 and 16 LMM portfolio companies during the three months ended September 30, 2025 and 2024, respectively, representing 27% and 24% of the total LMM portfolio at fair value as of September 30, 2025 and 2024, respectively. A total of 70 LMM portfolio companies were reviewed and certified by the Financial Advisory Firm during the trailing twelve months ended September 30, 2025, representing 92% of the total LMM portfolio at fair value as of September 30, 2025. Excluding its investments in LMM portfolio companies that, as of September 30, 2025, had not been in the Investment Portfolio for at least twelve months subsequent to the initial investment or whose primary purpose is to own real estate for which a third-party appraisal is obtained on at least an annual basis,99% of the LMM portfolio at fair value was reviewed and certified by the Financial Advisory Firm during the trailing twelve months ended September 30, 2025.

For valuation purposes, all of Main Street’s Private Loan portfolio investments are non-control investments. For Private Loan portfolio investments for which it has determined that third-party quotes or other independent pricing are not available or appropriate, Main Street generally estimates the fair value based on the assumptions that it believes hypothetical market participants would use to value such Private Loan debt investments in a current hypothetical sale using the Yield-to-Maturity valuation method and such Private Loan equity investments in a current hypothetical sale using the Waterfall valuation method.

In addition to its internal valuation process, in arriving at estimates of fair value for its investments in its Private Loan portfolio companies, Main Street, among other things, consults with the Financial Advisory Firm. The Financial Advisory Firm analyzes and provides observations, recommendations and an assurance certification regarding Main Street’s determinations of the fair value of its Private Loan portfolio company investments. The Financial Advisory Firm is generally consulted relative to Main Street’s investments in each Private Loan portfolio company at least once every calendar year, and for Main Street’s investments in new Private Loan portfolio companies, at least once in thetwelve-month period subsequent to the initial investment. In certain instances, Main Street may determine that it is not cost-effective, and as a result is not in its stockholders’ best interest, to consult with the Financial Advisory Firm on its investments in one or more Private Loan portfolio companies. Such instances include, but are not limited to, situations where the fair value of Main Street’s investment in a Private Loan portfolio company is determined to be insignificant relative to the total Investment Portfolio. Main Street consulted with and received an assurance certification from the Financial Advisory Firm in arriving at its determination of fair value for its investments in a total of 14 and 17 Private Loan portfolio companies during the three months ended September 30, 2025 and 2024, respectively, representing 26% and 24% of the total Private Loan portfolio at fair value as of September 30, 2025 and 2024, respectively. A total of 63 Private Loan portfolio companies were reviewed and certified by the Financial Advisory Firm during the trailing twelve months ended September 30, 2025, representing 94% of the total Private Loan portfolio at fair value as of September 30, 2025. Excluding its investments in Private Loan portfolio companies that, as of September 30, 2025, had not been in the Investment Portfolio for at least twelve months subsequent to the initial investment,97% of the Private Loan portfolio at fair value was reviewed and certified by the Financial Advisory Firm during the trailing twelve months ended September 30, 2025.

For valuation purposes, all of Main Street’s Middle Market portfolio investments are non-control investments. To the extent sufficient observable inputs are available to determine fair value, Main Street uses observable inputs to determine the fair value of these investments through obtaining third-party quotes or other independent pricing. For Middle Market portfolio investments for which it has determined that third-party quotes or other independent pricing are not available or appropriate, Main Street generally estimates the fair value based on the assumptions that it believes hypothetical market participants would use to value such Middle Market debt investments in a current hypothetical sale using the Yield-to-Maturity valuation method and such Middle Market equity investments in a current hypothetical sale using the Waterfall valuation method. Main Street generally consults on a limited basis with the Financial Advisory Firm in connection with determining the fair value of its Middle Market portfolio investments due to the nature of these investments. The vast majority (95% and 97% as of September 30, 2025 and December 31, 2024, respectively) of the Middle Market portfolio investments (i) are valued using third-party quotes or other independent pricing services or (ii) Main Street has consulted with and received an assurance certification from the Financial Advisory Firm within the last twelve months.

For valuation purposes, Main Street’s short-term portfolio investments have historically been comprised of non-control investments. To the extent sufficient observable inputs are available to determine fair value, Main Street uses observable inputs to determine the fair value of these investments through obtaining third-party quotes or other independent pricing. Because any short-term portfolio investments are typically valued using third-party quotes or other independent pricing services, Main Street generally does not consult with any financial advisory services firms in connection with determining the fair value of its short-term portfolio investments.

For valuation purposes, all of Main Street’s Other Portfolio investments are non-control investments. Main Street’s Other Portfolio investments comprised 2.4% and 2.5% of Main Street’s Investment Portfolio at fair value as of September 30, 2025 and December 31, 2024, respectively. Similar to the LMM investment portfolio, market quotations for Other Portfolio equity investments are generally not readily available. For its Other Portfolio equity investments, Main Street generally determines the fair value of these investments using the NAV valuation method.

For valuation purposes, Main Street’s investment in the External Investment Manager is a control investment. Market quotations are not readily available for this investment, and as a result, Main Street determines the fair value of the External Investment Manager using the Waterfall valuation method under the market approach. In estimating the enterprise value, Main Street analyzes various factors, including the entity’s historical and projected financial results, as well as its size, marketability and performance relative to the population of market comparables, and the valuations for comparable publicly traded companies and private transactions involving comparable companies. This valuation approach estimates the value of the investment as if Main Street were to sell, or exit, the investment. In addition, Main Street considers its ability to control the capital structure of the company, as well as the timing of a potential exit, in connection with determining the fair value of the External Investment Manager. Main Street consults with and receives an assurance certification from the Financial Advisory Firm in arriving at its determination of fair value for its investment in the External Investment Adviser on a quarterly basis, including as of September 30, 2025 and December 31, 2024.

Due to the inherent uncertainty in the valuation process, Main Street’s determination of fair value for its Investment Portfolio may differ materially from the values that would have been determined had a ready market for the securities existed. In addition, changes in the market environment, portfolio company performance and other events that may occur over the lives of the investments may cause the gains or losses ultimately realized on these investments to be materially different than the valuations currently assigned. Main Street determines the fair value of each individual investment and records changes in fair value as unrealized appreciation or depreciation.

Main Street uses an internally developed portfolio investment rating system in connection with its investment oversight, portfolio management and analysis and investment valuation procedures for its LMM, Private Loan and Middle Market portfolio companies. This system takes into account both quantitative and qualitative factors of each LMM, Private Loan and Middle Market portfolio company.

Rule 2a-5 under the 1940 Act permits a BDC’s board of directors to designate its executive officers or investment adviser as a valuation designee to determine the fair value for its investment portfolio, subject to the active oversight of the board. Main Street’s Board of Directors has approved policies and procedures pursuant to Rule 2a-5 (the “Valuation Procedures”) and has designated a group of its executive officers to serve as the Board of Directors’ valuation designee. Main Street believes its Investment Portfolio as of September 30, 2025 and December 31, 2024 approximates fair value as of those dates based on the markets in which it operates and other conditions in existence on those reporting dates.

2. Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the period. Actual results may differ from these estimates under different conditions or assumptions. Additionally, as explained in Note B.1. — Summary of Significant Accounting Policies — Valuation of the Investment Portfolio, the consolidated financial statements include investments in the Investment Portfolio whose values have been estimated by Main Street, pursuant to valuation policies and procedures approved and overseen by Main Street’s Board of Directors, in the absence of readily ascertainable market values. Because of the inherent uncertainty of the Investment Portfolio valuations, those estimated values may differ materially from the values that would have been determined had a ready market for the securities existed.

Macroeconomic factors, including pandemics, risk of recession, inflation, supply chain constraints or disruptions, geopolitical disruptions, uncertainty with respect to the imposition of tariffs on and trade disputes with certain countries and changing market index interest rates, and the related effect on the U.S. and global economies, have impacted, and may continue to impact, the businesses and operating results of certain of Main Street’s portfolio companies. As a result of these and other current effects of macroeconomic factors, as well as the uncertainty regarding the extent and duration of their impact, the valuation of Main Street’s Investment Portfolio has and may continue to experience increased volatility.

3. Cash and Cash Equivalents

Cash and cash equivalents consist of cash and highly liquid investments with an original maturity of three months or less at the date of purchase. Cash and cash equivalents are carried at cost, which approximates fair value. As of September 30, 2025 and December 31, 2024, the Company had $10.6 million and $6.5 million, respectively, of cash equivalents invested in AAA-rated money market funds pending investment in the Company’s primary investment strategies. These highly liquid investments are included in the Consolidated Schedule of Investments.

As of September 30, 2025 and December 31, 2024, cash balances totaling $17.0 million and $67.5 million, respectively, exceeded Federal Deposit Insurance Corporation insurance protection levels, subjecting the Company to risk related to the uninsured balance.

4. Interest, Dividend and Fee Income

Main Street records interest and dividend income on the accrual basis to the extent amounts are expected to be collected. Dividend income is recorded when dividends are declared by the portfolio company or at such other time that an obligation exists for the portfolio company to make a distribution. Main Street evaluates accrued interest and dividend income periodically for collectability. When a loan or debt security becomes 90 days or more past due, and if Main Street otherwise does not expect the debtor to be able to service its debt obligation, Main Street will generally place the loan or debt security on non-accrual status and cease recognizing interest income on that loan or debt security until the borrower has demonstrated the ability and intent to pay contractual amounts due. If a loan or debt security’s status significantly improves regarding the debtor’s ability to service the debt obligation, or if a loan or debt security is sold or written off, Main Street removes it from non-accrual status.

As of September 30, 2025, investments on non-accrual status comprised 1.2% of Main Street’s total Investment Portfolio at fair value and 3.6% at cost. As of December 31, 2024, investments on non-accrual status comprised 0.9% of Main Street’s total Investment Portfolio at fair value and 3.5% at cost.

Main Street holds certain debt and preferred equity instruments in its Investment Portfolio that contain PIK interest and cumulative dividend provisions. The PIK interest, computed at the contractual rate specified in each debt agreement, is periodically added to the principal balance of the debt and is recorded as interest income. Thus, the actual collection of this interest may be deferred until the time of debt principal repayment. Cumulative dividends are recorded as dividend income, and any dividends in arrears are added to the balance of the preferred equity investment. The actual collection of these dividends in arrears may be deferred until such time as the preferred equity is redeemed or sold. To maintain RIC tax treatment (as discussed in Note B.10. — Summary of Significant Accounting Policies — Income Taxes below), these non-cash sources of income may need to be paid out to stockholders in the form of distributions, even though Main Street may not have collected the PIK interest and cumulative dividends in cash. Main Street stops accruing PIK interest and cumulative dividends and writes off any accrued and uncollected interest and dividends in arrears when it determines that such PIK interest and dividends in arrears are no longer collectible. For the three months ended September 30, 2025 and 2024, (i)3.0% and 4.4%, respectively, of Main Street’s total investment income was attributable to PIK interest income not paid currently in cash and (ii)0.7% and 0.5%, respectively, of Main Street’s total investment income was attributable to cumulative dividend income not paid currently in cash. For the nine months ended September 30, 2025 and 2024, (i)2.7% and 3.8%, respectively, of Main Street’s total investment income was attributable to PIK interest income not paid currently in cash and (ii)0.7% and 0.4%, respectively, of Main Street’s total investment income was attributable to cumulative dividend income not paid currently in cash.

Main Street may periodically provide services, including structuring and advisory services, to its portfolio companies or other third parties. For services that are separately identifiable and evidence exists to substantiate fair value, fee income is recognized as earned, which is generally when the investment or other applicable transaction closes. Fees received in connection with debt financing transactions for services that do not meet these criteria are treated as debt origination fees and are generally deferred and accreted into income over the life of the financing.

A presentation of total investment income Main Street earned from its Investment Portfolio in each of the periods presented is as follows:

5. Deferred Financing Costs

Deferred financing costs include commitment fees and other direct costs related to Main Street’s Credit Facilities (as defined in Note E — Debt) and its unsecured notes, as well as the commitment fees and leverage fees (3.4% of the total commitment and draw amounts, as applicable) on the SBIC debentures. See further discussion of Main Street’s debt in Note E — Debt. Deferred financing costs incurred in connection with the Credit Facilities are capitalized as an asset. Deferred financing costs incurred in connection with all other debt arrangements are reflected as a direct deduction from the principal amount outstanding.

6. Equity Offering Costs

The Company’s offering costs are charged against the proceeds from equity offerings when the proceeds are received.

7. Unearned Income—Debt Origination Fees and Original Issue Discount and Discounts / Premiums to Par Value

Main Street capitalizes debt origination fees received in connection with financings and reflects such fees as unearned income netted against the applicable debt investments. The unearned income from the fees is accreted into income over the life of the financing.

In connection with its portfolio debt investments, Main Street sometimes receives nominal cost warrants or warrants with an exercise price below the fair value of the underlying equity (together, “nominal cost equity”) that are valued as part of the negotiation process with the particular portfolio company. When Main Street receives nominal cost equity, it allocates its cost basis in its investment between its debt security and its nominal cost equity at the time of origination based on amounts negotiated with the particular portfolio company. The allocated amounts are based upon the fair value of the nominal cost equity, which is then used to determine the allocation of cost to the debt security. Any discount recorded on a debt investment resulting from this allocation is reflected as unearned income, which is netted against the applicable debt investment, and accreted into interest income over the life of the debt investment. The actual collection of this interest is deferred until the time of debt principal repayment.

Main Street may also purchase debt securities at a discount or at a premium to the par value of the debt security. In the case of a purchase at a discount, Main Street records the investment at the par value of the debt security net of the discount, and the discount is accreted into interest income over the life of the debt investment. In the case of a purchase at a premium, Main Street records the investment at the par value of the debt security plus the premium, and the premium is amortized as a reduction to interest income over the life of the debt investment.

To maintain RIC tax treatment (as discussed in Note B.10. — Summary of Significant Accounting Policies — Income Taxes below), these non-cash sources of income may need to be paid out to stockholders in the form of distributions, even though Main Street may not have collected the interest income. For the three months ended September 30, 2025 and 2024,1.7% and 2.2%, respectively, of Main Street’s total investment income was attributable to interest income from the accretion of discounts associated with debt investments, net of any premium amortization. For the nine months ended September 30, 2025 and 2024,1.7% and 2.0%, respectively, of Main Street’s total investment income was attributable to interest income from the accretion of discounts associated with debt investments, net of any premium amortization.

8. Share-Based Compensation

Main Street accounts for its share-based compensation plans using the fair value method, as prescribed by ASC 718, Compensation—Stock Compensation. Accordingly, for restricted stock awards, Main Street measures the grant date fair value based upon the market price of its common stock on the date of the grant and amortizes the fair value of the awards as share-based compensation expense over the requisite service period, which is generally the vesting term.

Main Street recognizes all excess tax benefits and tax deficiencies associated with share-based compensation (including tax benefits of dividends on share-based payment awards) as tax expense or benefit in the income statement and does not delay recognition of a tax benefit until the tax benefit is realized through a reduction to taxes payable. As such, the tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. Additionally, Main Street has elected to account for forfeitures as they occur.

9. Deferred Compensation Plan

The Main Street Capital Corporation Deferred Compensation Plan (the “Deferred Compensation Plan”) allows directors and certain employees to defer receipt of some or all of their cash compensation or directors’ fees in accordance with plan terms. Deferred Compensation Plan participants elect one or more investment options, including phantom Main Street stock units, interests in affiliated funds and various mutual funds, where their deferred amounts are notionally invested, and Main Street invests the deferred amounts through a trust (except for phantom Main Street stock units), pending distribution.

Compensation deferred under the Deferred Compensation Plan is recognized on the same basis as such compensation would have been recognized if not deferred. The appreciation (depreciation) in the fair value of Deferred Compensation Plan assets is reflected in Main Street's Consolidated Statements of Operations as unrealized appreciation (depreciation), with the recognition of a corresponding and offsetting deferred compensation expense or (benefit), respectively. Deferred compensation expense or (benefit) does not result in a net cash impact to Main Street upon settlement. Investments in the trust are recognized on the Consolidated Balance Sheets as an asset of Main Street (other assets) and as a deferred compensation liability (other liabilities).

Phantom Main Street stock units under the Deferred Compensation Plan are not issued shares of Main Street common stock and are not included as outstanding on the Consolidated Statements of Changes in Net Assets until such shares are actually distributed to the participant, but the related phantom stock units are included in weighted-average shares outstanding with the related dollar amount of the deferral included in total expenses in Main Street’s Consolidated Statements of Operations as the deferred fees or compensation represented by such phantom stock units are earned over the service period. Additional phantom stock units from dividends on phantom stock units are included in the Consolidated Statements of Changes in Net Assets as an increase to dividends to stockholders offset by a corresponding increase to additional paid-in capital.

10. Income Taxes

MSCC has elected to be treated for U.S. federal income tax purposes as a RIC. MSCC’s taxable income includes the taxable income generated by MSCC and certain of its subsidiaries, including the Funds and Structured Subsidiaries, which are treated as disregarded entities for tax purposes. As a RIC, MSCC generally will not pay corporate-level U.S. federal income taxes on any net ordinary taxable income or capital gains that MSCC distributes to its stockholders. MSCC must generally distribute at least 90% of its “investment company taxable income” (which is generally its net ordinary taxable income and realized net short-term capital gains in excess of realized net long-term capital losses) and 90% of its tax-exempt income to maintain its RIC status (pass-through tax treatment for amounts distributed). As part of maintaining RIC status, undistributed taxable income (subject to a 4% non-deductible U.S. federal excise tax) pertaining to a given fiscal year may be distributed up to twelve months subsequent to the end of that fiscal year, provided such dividends are declared on or prior to the later of (i) the filing of the U.S. federal income tax return for the applicable fiscal year or (ii) the fifteenth day of the ninth month following the close of the year in which such taxable income was generated.

The Taxable Subsidiaries primarily hold certain equity investments for Main Street. The Taxable Subsidiaries permit Main Street to hold equity investments in portfolio companies which are “pass-through” entities for tax purposes and to continue to comply with the “source-of-income” requirements contained in the RIC tax provisions of the Code. The Taxable Subsidiaries are consolidated with Main Street for U.S. GAAP financial reporting purposes, and the portfolio investments held by the Taxable Subsidiaries are included in Main Street’s consolidated financial statements as portfolio investments and recorded at fair value. The Taxable Subsidiaries are not consolidated with MSCC for income tax purposes and may generate income tax expense, or benefit, and tax assets and liabilities, as a result of their ownership of certain portfolio investments. The taxable income, or loss, of the Taxable Subsidiaries may differ from their book income, or loss, due to temporary book and tax timing differences and permanent differences. The Taxable Subsidiaries are each taxed at corporate income tax rates based on their taxable income. The income tax expense, or benefit, if any, and the related tax assets and liabilities, of the Taxable Subsidiaries are reflected in Main Street’s consolidated financial statements.

The External Investment Manager is an indirect wholly-owned subsidiary of MSCC owned through a Taxable Subsidiary and is a disregarded entity for tax purposes. The External Investment Manager has entered into a tax sharing agreement with its Taxable Subsidiary owner. Since the External Investment Manager is accounted for as a portfolio investment of MSCC and is not included as a consolidated subsidiary of MSCC in MSCC’s consolidated financial statements, and as a result of the tax sharing agreement with its Taxable Subsidiary owner, for its stand-alone financial reporting purposes the External Investment Manager is treated as if it is taxed at corporate income tax rates based on its taxable income and, as a result of its activities, may generate income tax expense or benefit. The income tax expense, or benefit, if any, and the related tax assets and liabilities, of the External Investment Manager are reflected in the External Investment Manager’s separate financial statements.

The Taxable Subsidiaries and the External Investment Manager use the liability method in accounting for income taxes. Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and their reported amounts in the consolidated financial statements, using statutory tax rates in effect for the year in which the temporary differences are expected to reverse. A valuation allowance is provided, if necessary, against deferred tax assets when it is more likely than not that some portion or all of the deferred tax asset will not be realized. Main Street’s net assets as included on the Consolidated Balance Sheets and Consolidated Statements of Changes in Net Assets include an adjustment to classification as a result of permanent book-to-tax differences, which include differences in the book and tax treatment of income and expenses.

Taxable income generally differs from net income for financial reporting purposes due to temporary and permanent differences in the recognition of income and expenses. Taxable income generally excludes net unrealized appreciation or depreciation, as investment gains or losses are not included in taxable income until they are realized.

11. Net Realized Gains or Losses and Net Unrealized Appreciation or Depreciation

Realized gains or losses are measured by the difference between the net proceeds from the sale or redemption of an investment or a financial instrument and the cost basis of the investment or financial instrument, without regard to unrealized appreciation or depreciation previously recognized, and includes investments written-off during the period net of recoveries and realized gains or losses from in-kind redemptions. Net unrealized appreciation or depreciation reflects the net change in the fair value of the Investment Portfolio and financial instruments and the reclassification of any prior period unrealized appreciation or depreciation on exited investments and financial instruments to realized gains or losses.

12. Fair Value of Financial Instruments

Fair value estimates are made at discrete points in time based on relevant information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and, therefore, cannot be determined with precision. Main Street believes that the carrying amounts of its financial instruments, consisting of cash and cash equivalents, receivables, payables and other liabilities approximate the fair values of such items due to the short-term nature of these instruments.

Main Street’s debt instruments, including all revolving and term debt, are accounted for on a historical cost basis as applicable under U.S. GAAP. As also required under U.S. GAAP, Main Street discloses the estimated fair value of its debt obligations in Note E — Debt. To estimate the fair value of Main Street’s multiple tranches of unsecured debt instruments as disclosed in Note E — Debt, Main Street uses quoted market prices. For the estimated fair value of Main Street’s SBIC debentures, Main Street uses the Yield-to-Maturity valuation method based on projections of the discounted future free cash flows that the debt security will likely generate, including both the discounted cash flows of the associated interest and principal amounts for the debt security. The inputs used to value Main Street’s debt instruments for purposes of the fair value estimate disclosures in Note E — Debtare considered to be Level 2 according to the ASC 820 fair value hierarchy.

13. Earnings Per Share

Basic and diluted per share calculations, including net increase in net assets resulting from operations per share and net investment income per share, are computed utilizing the weighted-average number of shares of common stock outstanding for the period. In accordance with ASC 260, Earnings Per Share, the unvested shares of restricted stock awarded pursuant to Main Street’s equity compensation plans are participating securities and, therefore, are included in the basic earnings per share calculation. As a result, for all periods presented, there is no difference between diluted earnings per share and basic earnings per share amounts.

14. Segments

Main Street operates as a single segment with a principal investment objective to maximize total return by generating current income from debt investments and current income and capital appreciation from equity and equity-related investments. The Company’s Investment Committee and Chief Executive Officer collectively perform the function that allocates resources and assesses performance, and thus together, serve as the Company’s chief operating decision maker (the “CODM”). Among other metrics, the CODM uses net investment income as a primary U.S. GAAP profit or loss metric used in making operating decisions, which can be found on the Consolidated Statement of Operations along with significant expenses. The measure of segment assets is reported on the Consolidated Balance Sheets as total assets.

15. Recently Issued or Adopted Accounting Standards

In December 2023, the FASB issued ASU 2023-09, Improvements to Income Tax Disclosures. The amendments in this update require more disaggregated information on income taxes paid. ASU 2023-09 is effective for years beginning after December 15, 2024, and early adoption is permitted. The Company has determined that ASU 2023-09 will not have a material impact on the consolidated financial statements and the notes thereto.

From time to time, new accounting pronouncements are issued by the FASB or other standards-setting bodies that are adopted by the Company as of the specified effective date. The Company believes that the impact of recently issued standards and any that are not yet effective will not have a material impact on its consolidated financial statements upon adoption.

NOTE C —FAIR VALUE HIERARCHY FOR INVESTMENTS — PORTFOLIO COMPOSITION

ASC 820 defines fair value, establishes a framework for measuring fair value, establishes a fair value hierarchy based on the quality of inputs used to measure fair value, and enhances disclosure requirements for fair value measurements. Main Street accounts for its investments at fair value.

Fair Value Hierarchy

In accordance with ASC 820, Main Street has categorized its investments based on the priority of the inputs to the valuation technique into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical investments (Level 1) and the lowest priority to unobservable inputs (Level 3).

Investments recorded on Main Street’s Consolidated Balance Sheets are categorized based on the inputs to the valuation techniques as follows:

Level 1—Investments whose values are based on unadjusted quoted prices for identical assets in an active market that Main Street has the ability to access (examples include investments in active exchange-traded equity securities and investments in most U.S. government and agency securities).

Level 2—Investments whose values are based on quoted prices in markets that are not active or model inputs that are observable either directly or indirectly for substantially the full term of the investment. Level 2 inputs include the following:

•Quoted prices for similar assets in active markets (for example, investments in restricted stock);

•Quoted prices for identical or similar assets in non-active markets (for example, investments in thinly traded public companies);

•Pricing models whose inputs are observable for substantially the full term of the investment (for example, market interest rate indices); and

•Pricing models whose inputs are derived principally from, or corroborated by, observable market data through correlation or other means for substantially the full term of the investment.

Level 3—Investments whose values are based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement (for example, investments in illiquid securities issued by privately held companies). These inputs reflect management’s own assumptions about the assumptions a market participant would use in pricing the investment.

As required by ASC 820, when the inputs used to measure fair value fall within different levels of the hierarchy, the level within which the fair value measurement is categorized is based on the lowest level input that is significant to the fair value measurement in its entirety. For example, a Level 3 fair value measurement may include inputs that are observable (Levels 1 and 2) and unobservable (Level 3). Therefore, unrealized appreciation and depreciation related to such investments categorized within the Level 3 tables below may include changes in fair value that are attributable to both observable inputs (Levels 1 and 2) and unobservable inputs (Level 3).

As of September 30, 2025 and December 31, 2024, all of Main Street’s LMM portfolio investments consisted of illiquid securities issued by privately held companies and the fair value determination for these investments primarily consisted of unobservable inputs. As a result, all of Main Street’s LMM portfolio investments were categorized as Level 3 as of September 30, 2025 and December 31, 2024.

As of September 30, 2025 and December 31, 2024, Main Street’s Private Loan portfolio investments primarily consisted of illiquid securities issued by privately held companies. The fair value determination for these investments consisted of a combination of observable inputs in non-active markets for which sufficient observable inputs were not available to determine the fair value of these investments and unobservable inputs. As a result, all of Main Street’s Private Loan portfolio investments were categorized as Level 3 as of September 30, 2025 and December 31, 2024.

As of September 30, 2025 and December 31, 2024, Main Street’s Middle Market portfolio investments consisted primarily of investments in secured and unsecured debt investments and independently rated debt investments. The fair value determination for these investments consisted of a combination of observable inputs in non-active markets for which sufficient observable inputs were not available to determine the fair value of these investments and unobservable inputs. As a result, all of Main Street’s Middle Market portfolio investments were categorized as Level 3 as of September 30, 2025 and December 31, 2024.

As of September 30, 2025 and December 31, 2024, Main Street’s Other Portfolio investments consisted primarily of illiquid securities issued by privately held entities and the fair value determination for these investments primarily consisted of unobservable inputs. Main Street also has an equity investment in MSC Income Fund, Inc. (“MSC Income”), which began trading on the New York Stock Exchange (“NYSE”) on January 29, 2025. As a result, beginning on March 31, 2025, Main Street adjusted the basis in its valuation approach to align with the quoted price of MSC Income shares on the NYSE. Therefore, as of September 30, 2025, the equity investment in MSC Income was categorized as a Level 1 investment. The remainder of Main Street’s Other Portfolio investments were categorized as Level 3 as of September 30, 2025 and December 31, 2024.

As of September 30, 2025 and December 31, 2024, Main Street didnot hold any short-term portfolio investments.

As of September 30, 2025 and December 31, 2024, all money market funds included in cash and cash equivalents were valued using Level 1 inputs.

The fair value determination of each portfolio investment categorized as Level 3 required one or more of the following unobservable inputs:

•Financial information obtained from each portfolio company, including unaudited statements of operations and balance sheets for the most recent period available as compared to budgeted numbers;

•Current and projected financial condition of the portfolio company;

•Current and projected ability of the portfolio company to service its debt obligations;

•Type and amount of collateral, if any, underlying the investment;

•Current financial ratios (e.g., fixed charge coverage ratio, interest coverage ratio and net debt/EBITDA ratio) applicable to the investment;

•Current liquidity of the investment and related financial ratios (e.g., current ratio and quick ratio);

•Pending debt or capital restructuring of the portfolio company;

•Projected operating results of the portfolio company;

•Current information regarding any offers to purchase the investment;

•Current ability of the portfolio company to raise any additional financing as needed;

•Changes in the economic environment which may have a material impact on the operating results of the portfolio company;

•Internal occurrences that may have an impact (both positive and negative) on the operating performance of the portfolio company;

•Qualitative assessment of key management;

•Contractual rights, obligations or restrictions associated with the investment; and

•Other factors deemed relevant.

The use of significant unobservable inputs creates uncertainty in the measurement of fair value as of the reporting date. The significant unobservable inputs used in the fair value measurement of Main Street’s LMM equity securities, which are generally valued through an average of the discounted cash flow technique and the market comparable/enterprise value technique (unless one of these approaches is determined to not be appropriate), are (i) EBITDA multiples and (ii) the weighted-average cost of capital (“WACC”). Significant increases (decreases) in EBITDA multiple inputs in isolation would result in a significantly higher (lower) fair value measurement, and significant increases (decreases) in WACC inputs in isolation would result in a significantly lower (higher) fair value measurement. The significant unobservable inputs used in the fair value measurement of Main Street’s LMM, Private Loan and Middle Market debt securities are (i) risk adjusted discount rates used in the Yield-to-Maturity valuation technique (see Note B.1. — Summary of Significant Accounting Policies — Valuation of the Investment Portfolio) and (ii) the percentage of expected principal recovery. Significant increases (decreases) in any of these discount rates in isolation would result in a significantly lower (higher) fair value measurement. Significant increases (decreases) in any of these expected principal recovery percentages in isolation would result in a significantly higher (lower) fair value measurement. However, due to the nature of certain investments, fair value measurements may be based on other criteria, such as third-party appraisals of collateral and fair values as determined by independent third parties, which are not presented in the tables below.

The following tables provide a summary of the significant unobservable inputs used to fair value Main Street’s Level 3 portfolio investments as of September 30, 2025 and December 31, 2024:

(1)EBITDA may include proforma adjustments and/or other add-backs based on specific circumstances related to each investment.

(2)Range excludes outliers that are greater than one standard deviation from the mean. Including these outliers, the range for EBITDA multiple is 2.0 x -16.0 x and the range for risk adjusted discount rate is 5.7% -40.6%.

(3)The fair value of the equity investment in the External Investment Manager is based on a fee multiple of 8.4 x. The fair value determination is based on a discounted, blended multiple based on the multiples for similar businesses in active markets and actual multiples used in private transactions.

(4)Does not include investments for which the valuation technique does not include the use of the applicable fair value input.

(5)Weighted-average is calculated for each significant unobservable input based on the applicable security’s fair value.

(6)Discount rate includes the effect of the standard SOFR base rate, as applicable.

(1)EBITDA may include proforma adjustments and/or other add-backs based on specific circumstances related to each investment.

(2)Range excludes outliers that are greater than one standard deviation from the mean. Including these outliers, the range for EBITDA multiple is 2.0 x -17.0 x and the range for risk adjusted discount rate is 5.0% -38.3%.

(3)The fair value of the equity investment in the External Investment Manager is based on a fee multiple of 8.5 x. The fair value determination is based on a discounted, blended multiple based on the multiples for similar businesses in active markets and actual multiples used in private transactions.

(4)Does not include investments for which the valuation technique does not include the use of the applicable fair value input.

(5)Weighted-average is calculated for each significant unobservable input based on the applicable security’s fair value.

(6)Discount rate includes the effect of the standard SOFR base rate, as applicable.

The following tables provide a summary of changes in fair value of Main Street’s Level 3 portfolio investments for the nine months ended September 30, 2025 and 2024 (amounts in thousands):

(1)Includes the impact of non-cash conversions. These transactions represent non-cash investing activities. See additional cash flow information in the Consolidated Statements of Cash Flows.

(1)Includes the impact of non-cash conversions. These transactions represent non-cash investing activities. See additional cash flow information in the Consolidated Statements of Cash Flows.

As of September 30, 2025 and December 31, 2024, Main Street’s investments at fair value were categorized as follows in the fair value hierarchy for ASC 820 purposes:

Investment Portfolio Composition

Main Street’s principal investment objective is to maximize its portfolio’s total return by generating current income from its debt investments and current income and capital appreciation from its equity and equity-related investments, including warrants, convertible securities and other rights to acquire equity securities in a portfolio company. Main Street seeks to achieve its investment objective primarily through its LMM and Private Loan investment strategies.

Main Street’s LMM investment strategy is focused on investments in secured debt and equity investments in privately held, LMM companies based in the United States. Main Street’s LMM portfolio companies generally have annual revenues between $10 million and $150 million, and its LMM investments generally range in size from $5 million to $125 million. The LMM debt investments are typically secured by a first priority lien on the assets of the portfolio company, can include either fixed or floating interest rates and generally have a term of between five andseven years from the original investment date. Main Street typically makes direct equity investments and/or receives nominally priced equity warrants in connection with a LMM portfolio company debt investment.

Main Street’s Private Loan investment strategy is focused on investments in secured debt in privately held companies that generally have annual revenues between $25 million and $500 million, and its Private Loan investments generally range in size from $10 million to $100 million. Main Street’s Private Loan investments primarily consist of debt securities that have primarily been originated directly by Main Street or, to a lesser extent, through its strategic relationships with other investment funds on a collaborative basis through investments that are often referred to in the debt markets as “club deals” because of the small lender group size. In both cases, Main Street’s Private Loan investments are typically made in a company owned by or in the process of being acquired by a private equity fund. Main Street’s Private Loan portfolio debt investments are generally secured by a first priority lien on the assets of the portfolio company and typically have a term of between three andseven years from the original investment date. Main Street may also co-invest with the private equity fund in the equity securities of its Private Loan portfolio companies.

Main Street also maintains a legacy portfolio of investments in Middle Market companies. Main Street’s Middle Market investments are generally debt investments in companies owned by a private equity fund that were originally issued through a syndication financing process. Main Street has generally stopped making new Middle Market investments and expects the size of its Middle Market investment portfolio to continue to decline in future periods as its existing Middle Market investments are repaid or sold. Main Street’s Middle Market debt investments generally range in size from $3 million to $25 million, are generally secured by a first priority lien on the assets of the portfolio company and typically have an expected duration of between three andseven years from the original investment date.

Main Street’s Other Portfolio investments primarily consist of investments that are not consistent with the typical profiles for its LMM, Private Loan or Middle Market portfolio investments, including investments which may be managed by third parties. In the Other Portfolio, Main Street may incur indirect fees and expenses in connection with investments managed by third parties, such as investments in other investment companies or private funds. For Other Portfolio investments, Main Street generally receives distributions related to the assets held by the portfolio company. Those assets are typically expected to be realized over afive toten-year period.

Based upon Main Street’s liquidity and capital structure management activities, Main Street’s Investment Portfolio may also periodically include short-term portfolio investments that are atypical of Main Street’s LMM, Private Loan and Middle Market portfolio investments in that they are intended to be a short-term deployment of capital. Those assets are typically expected to be realized inone year or less. These short-term portfolio investments are not expected to be a significant portion of the overall Investment Portfolio.

Main Street’s external asset management business is conducted through its External Investment Manager. The External Investment Manager earns management fees based on the assets under management for External Parties and may earn incentive fees, or a carried interest, based on the performance of the assets managed. Main Street entered into an agreement with the External Investment Manager to share employees in connection with its asset management business generally, and specifically for its relationship with MSC Income and its other clients. Through this agreement, Main Street shares employees with the External Investment Manager, including their related infrastructure, business relationships, management expertise and capital raising capabilities. Main Street allocates the related expenses to the External Investment Manager pursuant to the sharing agreement. Main Street’s total expenses are net of expenses allocated to the External Investment Manager of $5.7 million and $5.3 million for the three months ended September 30, 2025 and 2024, respectively, and $17.0 million and $16.8 million for the nine months ended September 30, 2025 and 2024, respectively.

Investment income, consisting of interest, dividends and fees, can fluctuate dramatically due to various factors, including the level of new investment activity, repayments of debt investments or sales of equity interests. Investment income in any given year could also be highly concentrated among several portfolio companies. For the three and nine months ended September 30, 2025 and 2024, Main Street did not record investment income from any single portfolio company in excess of 10% of total investment income.

The following tables provide a summary of Main Street’s investments in the LMM and Private Loan portfolios as of September 30, 2025 and December 31, 2024 (this information excludes Middle Market, Other Portfolio investments and the External Investment Manager, which are discussed further below).

(a)As of September 30, 2025, Main Street had equity ownership in all of its LMM portfolio companies, and the average fully diluted equity ownership in those portfolio companies was 38%.

(b)The weighted-average annual effective yields were computed using the effective interest rates for all debt investments as of September 30, 2025, including amortization of deferred debt origination fees and accretion of original issue discount but excluding fees payable upon repayment of the debt instruments and any debt investments on non-accrual status, and are weighted based upon the principal amount of each applicable debt investment as of September 30, 2025. The weighted-average annual effective yield on Main Street’s debt portfolio as of September 30, 2025, including debt investments on non-accrual status, was 12.1% for its LMM portfolio and 10.1% for its Private Loan portfolio. The weighted-average annual effective yield is not reflective of what an investor in shares of Main Street’s common stock will realize on its investment because it does not reflect changes in the market value of Main Street’s stock, Main Street’s utilization of debt capital in its capital structure, Main Street’s expenses or any sales load paid by an investor.

(c)The average EBITDA is calculated using a simple average for the LMM portfolio and a weighted-average for the Private Loan portfolio. These calculations exclude certain portfolio companies, including five LMM portfolio companies andsix Private Loan portfolio companies, as EBITDA is not a meaningful valuation metric for Main Street’s investments in these portfolio companies, and those portfolio companies whose primary purpose is to own real estate and those portfolio companies whose primary operations have ceased and only residual value remains.

(a)As of December 31, 2024, Main Street had equity ownership in all of its LMM portfolio companies, and the average fully diluted equity ownership in those portfolio companies was 38%.

(b)The weighted-average annual effective yields were computed using the effective interest rates for all debt investments as of December 31, 2024, including amortization of deferred debt origination fees and accretion of original issue discount but excluding fees payable upon repayment of the debt instruments and any debt investments on non-accrual status, and are weighted based upon the principal amount of each applicable debt investment as of December 31, 2024. The weighted-average annual effective yield on Main Street’s debt portfolio as of December 31, 2024, including debt investments on non-accrual status, was 12.3% for its LMM portfolio and 11.5% for its Private Loan portfolio. The weighted-average annual effective yield is not reflective of what an investor in shares of Main Street’s common stock will realize on its investment because it does not reflect changes in the market value of Main Street’s stock, Main Street’s utilization of debt capital in its capital structure, Main Street’s expenses or any sales load paid by an investor.

(c)The average EBITDA is calculated using a simple average for the LMM portfolio and a weighted-average for the Private Loan portfolio. These calculations exclude certain portfolio companies, including five LMM portfolio companies andfive Private Loan portfolio companies, as EBITDA is not a meaningful valuation metric for Main Street’s investments in these portfolio companies, and those portfolio companies whose primary purpose is to own real estate and those portfolio companies whose primary operations have ceased and only residual value remains.

For the three months ended September 30, 2025 and 2024, Main Street achieved an annualized total return on investments of 16.9% and 17.7%, respectively. For the nine months ended September 30, 2025 and 2024, Main Street achieved an annualized total return on investments of 16.4% and 16.7%, respectively. For the year ended December 31, 2024, Main Street achieved a total return on investments of 17.9%. Total return on investments is calculated using the interest, dividend and fee income, as well as the realized and unrealized change in fair value of the Investment Portfolio for the specified period. Main Street’s total return on investments is not reflective of what an investor in shares of Main Street’s common stock will realize on its investment because it does not reflect changes in the market value of Main Street’s stock, Main Street’s utilization of debt capital in its capital structure, Main Street’s expenses or any sales load paid by an investor.

As of September 30, 2025, Main Street had Other Portfolio investments in 32 entities, spread across 12 investment managers, collectively totaling $122.8 million in fair value and $130.9 million in cost basis, which comprised 2.4% and 3.0% of Main Street’s Investment Portfolio at fair value and cost, respectively. As of December 31, 2024, Main Street had Other Portfolio investments in 31 entities, spread across 12 investment managers, collectively totaling $124.1 million in fair value and $122.5 million in cost basis, which comprised 2.5% and 2.9% of Main Street’s Investment Portfolio at fair value and cost, respectively.

As of September 30, 2025, Main Street had Middle Market portfolio investments in 11 portfolio companies, collectively totaling $89.9 million in fair value and $119.8 million in cost basis, which comprised 1.7% and 2.8% of Main Street’s Investment Portfolio at fair value and cost, respectively. As of December 31, 2024, Main Street had Middle Market portfolio investments in 15 portfolio companies, collectively totaling $155.3 million in fair value and $195.0 million in cost basis, which comprised 3.1% and 4.6% of Main Street’s Investment Portfolio at fair value and cost, respectively.

As discussed further in Note A.1. — Organization and Basis of Presentation — Organization, Main Street holds an investment in the External Investment Manager, a wholly-owned subsidiary that is treated as a portfolio investment. As of September 30, 2025, this investment had a fair value of $266.4 million and a cost basis of $29.5 million, which comprised 5.2% and 0.7% of Main Street’s Investment Portfolio at fair value and cost, respectively. As of December 31, 2024, this investment had a fair value of $246.0 million and a cost basis of $29.5 million, which comprised 5.0% and 0.7% of Main Street’s Investment Portfolio at fair value and cost, respectively.

The following tables summarize the composition of Main Street’s total combined LMM, Private Loan and Middle Market portfolio investments at cost and fair value by type of investment as a percentage of the total combined LMM, Private Loan and Middle Market portfolio investments, as of September 30, 2025 and December 31, 2024 (this information excludes Other Portfolio investments and the External Investment Manager, which are discussed above).

The following tables summarize the composition of Main Street’s total combined LMM, Private Loan and Middle Market portfolio investments by geographic region of the United States and other countries at cost and fair value as a percentage of the total combined LMM, Private Loan and Middle Market portfolio investments, as of September 30, 2025 and December 31, 2024 (this information excludes Other Portfolio investments and the External Investment Manager). The geographic composition is determined by the location of the corporate headquarters of the portfolio company.

Main Street’s LMM, Private Loan and Middle Market portfolio investments are in companies conducting business in a variety of industries. The following tables summarize the composition of Main Street’s total combined LMM, Private Loan and Middle Market portfolio investments by industry at cost and fair value as of September 30, 2025 and December 31, 2024 (this information excludes Other Portfolio investments and the External Investment Manager).

(1)Includes various industries with each industry individually less than 1.0% of the total combined LMM, Private Loan and Middle Market portfolio investments at each date.

(1)Includes various industries with each industry individually less than 1.0% of the total combined LMM, Private Loan and Middle Market portfolio investments at each date.

As of September 30, 2025 and December 31, 2024, Main Street had no portfolio investment that was greater than 10% of the Investment Portfolio at fair value.

Unconsolidated Significant Subsidiaries

In accordance with Rules 3-09 and 4-08(g) of Regulation S-X, Main Street must determine which of its unconsolidated controlled portfolio companies, if any, are considered “significant subsidiaries.” In evaluating its unconsolidated controlled portfolio companies in accordance with Regulation S-X, there are two tests that Main Street must utilize to determine if any of Main Street’s Control investments (as defined in Note A — Organization and Basis of Presentation), including those unconsolidated portfolio companies defined as Control investments in which Main Street does not own greater than 50% of the voting securities nor have rights to maintain greater than 50% of the board representation, are considered significant subsidiaries: the investment test and the income test. The investment test is generally measured by dividing the fair value of Main Street’s investment in the Control investment by the fair value of Main Street’s total investments. The income test is generally measured by dividing the absolute value of the combined sum of total investment income, net realized gain (loss) and net unrealized appreciation (depreciation) from the relevant Control investment for the period being tested by the absolute value of Main Street’s change in net assets resulting from operations for the same period. Rules 3-09 and 4-08(g) of Regulation S-X require Main Street to include (1) separate audited financial statements of an unconsolidated majority-owned subsidiary (Control investments in which Main Street owns greater than 50% of the voting securities) in an annual report and (2) summarized financial information of a Control investment in a quarterly report, respectively, if certain thresholds of the investment or income tests are exceeded and the unconsolidated portfolio company qualifies as a significant subsidiary.

As of September 30, 2025 and December 31, 2024, Main Street had no single investment that qualified as a significant subsidiary under either the investment or income tests.

NOTE D —EXTERNAL INVESTMENT MANAGER

As discussed further in Note A.1. — Organization and Basis of Presentation — Organization and Note C — Fair Value Hierarchy for Investments — Portfolio Composition — Investment Portfolio Composition, the External Investment Manager provides investment management and other services to External Parties. The External Investment Manager is accounted for as a portfolio investment of Main Street since the External Investment Manager conducts all of its investment management activities for External Parties.

The External Investment Manager serves as the investment adviser and administrator to MSC Income pursuant to an Investment Advisory and Administrative Services Agreement entered into in October 2020 between the External Investment Manager and MSC Income (as amended and restated on January 29, 2025, the “Advisory Agreement”). Under the Advisory Agreement, prior to January 29, 2025, the External Investment Manager earned a 1.75% annual base management fee on MSC Income’s average total assets, a subordinated incentive fee on income equal to 20% of pre-incentive fee net investment income above a specified investment return hurdle rate and a 20% incentive fee on cumulative net realized capital gains in exchange for providing advisory services to MSC Income. On and after January 29, 2025, under the Advisory Agreement, the External Investment Manager earns a 1.5% annual base management fee on MSC Income’s average total assets (including cash and cash equivalents), payable quarterly in arrears (with additional future contractual reductions based upon changes to MSC Income’s investment portfolio composition), a subordinated incentive fee on income equal to 17.5% of pre-incentive fee net investment income above a specified investment return hurdle rate, subject to a 50% / 50% catch-up feature, and a 17.5% incentive fee on cumulative net realized capital gains from January 29, 2025.

As described more fully in Note L — Related Party Transactions, the External Investment Manager also serves as the investment adviser and administrator to MS Private Loan Fund I, LP ( “Private Loan Fund I”) and MS Private Loan Fund II, LP (“Private Loan Fund II”), each a private investment fund with a strategy to co-invest with Main Street in Private Loan portfolio investments. The External Investment Manager entered into investment management agreements in December 2020 with Private Loan Fund I and in September 2023 with Private Loan Fund II, pursuant to which the External Investment Manager provides investment advisory and management services to each fund in exchange for an asset-based fee and certain incentive fees. The External Investment Manager may also advise other clients, including funds and separately managed accounts, pursuant to advisory and services agreements with such clients in exchange for asset-based and incentive fees.

The External Investment Manager provides administrative services for certain External Party clients that, to the extent not waived, are reported as administrative services fees. The administrative services fees generally represent expense reimbursements for a portion of the compensation, overhead and related expenses for certain professionals directly attributable to performing administrative services for clients. These fees are recognized as other revenue in the period in which the related services are rendered.

Main Street determines the fair value of the External Investment Manager using the Waterfall valuation method under the market approach (see further discussion in Note B.1. — Summary of Significant Accounting Policies — Valuation of the Investment Portfolio). Any change in fair value of the investment in the External Investment Manager is recognized on Main Street’s Consolidated Statements of Operations in “Net Unrealized Appreciation — Control investments.”

The External Investment Manager is an indirect wholly-owned subsidiary of MSCC owned through a Taxable Subsidiary and is a disregarded entity for tax purposes. The External Investment Manager has entered into a tax sharing agreement with its Taxable Subsidiary owner. Since the External Investment Manager is accounted for as a portfolio investment of Main Street and is not included as a consolidated subsidiary of Main Street in its consolidated financial statements, and as a result of the tax sharing agreement with its Taxable Subsidiary owner, for financial reporting purposes the External Investment Manager is treated as if it is taxed at corporate income tax rates based on its taxable income and, as a result of its activities, may generate income tax expense or benefit. Main Street owns the External Investment Manager through the Taxable Subsidiary to allow MSCC to continue to comply with the “source-of-income” requirements contained in the RIC tax provisions of the Code. The taxable income, or loss, of the External Investment Manager may differ from its book income, or loss, due to temporary book and tax timing differences and permanent differences. As a result of the above described financial reporting and tax treatment, the External Investment Manager provides for any income tax expense, or benefit, and any tax assets or liabilities in its separate financial statements.

Main Street shares employees with the External Investment Manager and allocates costs related to such shared employees to the External Investment Manager generally based on a combination of the direct time spent, new investment activities and assets under management, depending on the nature of the expense. The total contribution of the External Investment Manager to Main Street’s net investment income consists of the combination of the expenses allocated to the External Investment Manager and the dividend income earned from the External Investment Manager. For the three months ended September 30, 2025 and 2024, the total contribution to Main Street’s net investment income was $8.8 million and $7.9 million, respectively. For the nine months ended September 30, 2025 and 2024, the total contribution to Main Street’s net investment income was $25.4 million and $25.6 million, respectively.

Summarized financial information from the separate financial statements of the External Investment Manager as of September 30, 2025 and December 31, 2024 and for the three and nine months ended September 30, 2025 and 2024 is as follows:

NOTE E —DEBT

Summary of Main Street’s debt as of September 30, 2025 is as follows:

(1)The unamortized debt issuance costs for the Credit Facilities are reflected as Deferred financing costs on the Consolidated Balance Sheets, while the deferred debt issuance costs related to the July 2026 Notes, June 2027 Notes, August 2028 Notes, March 2029 Notes and SBIC debentures are reflected as contra-liabilities on the Consolidated Balance Sheets.

(2)Estimated fair value for outstanding debt is shown as if Main Street had adopted the fair value option under ASC 825. See discussion of the methods used to estimate the fair value of Main Street’s debt in Note B.12. — Summary of Significant Accounting Policies — Fair Value of Financial Instruments.

Summary of Main Street’s debt as of December 31, 2024 is as follows:

(1)The unamortized debt issuance costs for the Credit Facilities are reflected as Deferred financing costs on the Consolidated Balance Sheets, while the deferred debt issuance costs related to the July 2026 Notes, June 2027 Notes, March 2029 Notes, SBIC debentures and December 2025 Notes are reflected as contra-liabilities on the Consolidated Balance Sheets.

(2)Estimated fair value for outstanding debt is shown as if Main Street had adopted the fair value option under ASC 825. See discussion of the methods used to estimate the fair value of Main Street’s debt in Note B.12. — Summary of Significant Accounting Policies — Fair Value of Financial Instruments.

Summarized interest expense for the three and nine months ended September 30, 2025 and 2024 is as follows:

A summary of Main Street’s average amount of total borrowings outstanding and overall weighted-average effective interest rate including amortization of debt issuance costs, original issuance discounts and premiums and fees on unused lender commitments are as follows:

Corporate Facility

Main Street maintains a multi-year revolving credit facility (the “Corporate Facility”) to provide additional liquidity to support its investment and operational activities. In April 2025, Main Street entered into an amendment to the Corporate Facility to, among other things: (i) decrease the interest rate to the applicable SOFR plus a credit spread adjustment of 0.10% plus (a)1.775% prior to satisfying certain step-down conditions or (b)1.65% after satisfying certain step-down conditions, (ii) increase the revolving commitments to $1.145 billion, (iii) increase the accordion feature providing Main Street with the right to request increases in commitments under the facility from new and existing lenders on the same terms and conditions as the existing commitments to up to a total of $1.718 billion and (iv) extend the revolving period and final maturity date through April 2029 and to April 2030, respectively.

As of September 30, 2025, the Corporate Facility included (i) total commitments of $1.145 billion from a diversified group of 19 lenders, (ii) an accordion feature with the right to request an increase in commitments under the facility from new and existing lenders on the same terms and conditions as the existing commitments up to a total of $1.718 billion and (iii) a revolving period through April 2029 and a final maturity date in April 2030.

As of September 30, 2025, borrowings under the Corporate Facility bore interest, subject to Main Street’s election and resetting on a monthly basis on the first of each month, at a rate equal to the applicable SOFR plus a credit spread adjustment of 0.10% plus 1.775% (or 1.65% after satisfying certain step-down conditions in the future). Main Street pays unused commitment fees of 0.25% on the unused lender commitments under the Corporate Facility. The Corporate Facility is secured by a first lien on the assets of MSCC and its subsidiaries, excluding the equity ownership and assets of the Funds, the Structured Subsidiaries and the External Investment Manager. In connection with the Corporate Facility, MSCC has made customary representations and warranties and is subject to certain leverage and borrowing base limitations, covenants, reporting and other requirements customary for similar credit facilities.

As of September 30, 2025, the interest rate for borrowings on the Corporate Facility was 6.2%. The average interest rate for borrowings under the Corporate Facility was 6.2% and 7.3% for the three months ended September 30, 2025 and 2024, respectively, and 6.2% and 7.3% for the nine months ended September 30, 2025 and 2024, respectively. As of September 30, 2025, Main Street was in compliance with all financial covenants of the Corporate Facility.

SPV Facility

Main Street, through MSCC Funding I, LLC (“MSCC Funding”), a wholly-owned Structured Subsidiary that primarily holds debt investments, maintains a special purpose vehicle revolving credit facility (the “SPV Facility” and, together with the Corporate Facility, the “Credit Facilities”) to finance its investment and operational activities. In April 2025, Main Street entered into an amendment to the SPV Facility to, among other things: (i) decrease the interest rate to the applicable SOFR plus an applicable margin of (a)1.95% during the revolving period (from 2.35%), (b)2.075% for the first year following the end of the revolving period (from 2.475%) and (c)2.20% for the second year following the end of the revolving period (from 2.60%), (ii) extend the revolving period from through September 2027 to through September 2028, (iii) extend the final maturity date from September 2029 to September 2030 and (iv) decrease the unused fee to 0.40% (from 0.50%) on the unused amount up to 50% (from 35%) of the commitment amount.

As of September 30, 2025, the SPV Facility included (i) total commitments of $600.0 million from a diversified group ofsix lenders, (ii) an accordion feature providing MSCC Funding with the right to request increases in commitments under the facility, subject to the satisfaction of various conditions, from new and existing lenders on the same terms and conditions as the existing commitments to up to a total of $800.0 million and (iii) a revolving period through September 2028 and a final maturity date in September 2030. Advances under the SPV Facility bear interest at a rate equal to the applicable SOFR in effect, plus an applicable margin of 1.95% during the revolving period and 2.075% and 2.20% during the first and second years thereafter, respectively. MSCC Funding pays a commitment fee of 0.40% on the unused lender commitments up to 50% of the total lender commitments and 0.75% on the unused lender commitments greater than 50% of the total lender commitments. The SPV Facility is secured by a first lien loan on the assets of MSCC Funding and its subsidiaries. In connection with the SPV Facility, MSCC Funding has made customary representations and warranties and is subject to certain leverage and borrowing base limitations, covenants, reporting and other requirements customary for similar credit facilities.

As of September 30, 2025, the interest rate for borrowings on the SPV Facility was 6.2%. The average interest rate for borrowings under the SPV Facility was 6.3% and 7.9% for the three months ended September 30, 2025 and 2024, respectively, and 6.4% and 7.9% for the nine months ended September 30, 2025 and 2024, respectively. As of September 30, 2025, MSCC Funding was in compliance with all financial covenants of the SPV Facility.

MSCC Funding’s balance sheets as of September 30, 2025 and December 31, 2024 are as follows:

Balance Sheets

MSCC Funding’s statements of operations for the three and nine months ended September 30, 2025 and 2024 are as follows:

Statements of Operations

July 2026 Notes

In January 2021, Main Street issued $300.0 million in aggregate principal amount of 3.00% unsecured notes due July 14, 2026 (the “July 2026 Notes”) at an issue price of 99.004%. Subsequently, in October 2021, Main Street issued an additional $200.0 million in aggregate principal amount of the July 2026 Notes at an issue price of 101.741%. The July 2026 Notes issued in October 2021 have identical terms as, and are a part of a single series with, the July 2026 Notes issued in January 2021. The July 2026 Notes are unsecured obligations and rank pari passu with Main Street’s current and future unsecured indebtedness. The July 2026 Notes may be redeemed in whole or in part at any time at Main Street’s option subject to certain make-whole provisions. The July 2026 Notes bear interest at a rate of 3.00% per year payable semiannually on January 14 and July 14 of each year.

As of September 30, 2025, Main Street was in compliance with all covenants and other requirements of the July 2026 Notes.

June 2027 Notes

In June 2024, Main Street issued $300.0 million in aggregate principal amount of 6.50% unsecured notes due June 4, 2027 (the “June 2027 Notes”) at an issue price of 99.793%. Subsequently, in September 2024, Main Street issued an additional $100.0 million in aggregate principal amount of the June 2027 Notes at a public offering price of 102.134% resulting in a yield-to-maturity of 5.617% on such issuance. The $400.0 million of outstanding June 2027 Notes bear interest at 6.50% per year with a yield-to-maturity of 6.34%. The June 2027 Notes issued in September 2024 have identical terms as, and are a part of a single series with, the June 2027 Notes issued in June 2024. The June 2027 Notes are unsecured obligations and rank pari passu with Main Street’s current and future unsecured indebtedness. The June 2027 Notes may be redeemed in whole or in part at any time at Main Street’s option subject to certain make-whole provisions. The June 2027 Notes bear interest at a rate of 6.50% per year payable semiannually on June 4 and December 4 of each year.

As of September 30, 2025, Main Street was in compliance with all covenants and other requirements of the June 2027 Notes.

August 2028 Notes

In August 2025, Main Street issued $350.0 million in aggregate principal amount of 5.40% unsecured notes due August 15, 2028 (the “August 2028 Notes”) at an issue price of 99.989%. The August 2028 Notes are unsecured obligations and rank pari passu with Main Street’s current and future unsecured indebtedness. The August 2028 Notes may be redeemed in whole or in part at any time at Main Street’s option subject to certain make-whole provisions. The August 2028 Notes bear interest at a rate of 5.40% per year payable semiannually on February 15 and August 15 of each year.

As of September 30, 2025, Main Street was in compliance with all covenants and other requirements of the August 2028 Notes.

March 2029 Notes

In January 2024, Main Street issued $350.0 million in aggregate principal amount of 6.95% unsecured notes due March 1, 2029 (the “March 2029 Notes”) at an issue price of 99.865%. The March 2029 Notes are unsecured obligations and rank pari passu with Main Street’s current and future unsecured indebtedness. The March 2029 Notes may be redeemed in whole or in part at any time at Main Street’s option subject to certain make-whole provisions. The March 2029 Notes bear interest at a rate of 6.95% per year payable semiannually on March 1 and September 1 of each year.

As of September 30, 2025, Main Street was in compliance with all covenants and other requirements of the March 2029 Notes.

SBIC Debentures

Under existing SBIC regulations, SBA-approved SBICs under common control have the ability to issue debentures guaranteed by the SBA up to a regulatory maximum amount of $350.0 million. Under existing SBA-approved commitments, Main Street, through the Funds, had $350.0 million of outstanding SBIC debentures as of both September 30, 2025 and December 31, 2024. SBIC debentures provide for interest to be paid semiannually, with principal due at the applicable 10-year maturity date of each debenture. The principal amount of the debentures is not required to be paid before maturity, but may be pre-paid at any time with no prepayment penalty. The weighted-average annual interest rate on the SBIC debentures was 3.3% as of both September 30, 2025 and December 31, 2024. The first principal maturity due under the existing SBIC debentures is in 2027, and the weighted-average remaining duration as of September 30, 2025 was 4.9 years. In accordance with SBIC regulations, the Funds are precluded from incurring additional non-SBIC debt without the prior approval of the SBA. Main Street expects to maintain SBIC debentures under the SBIC program in the future, subject to periodic repayments and borrowings, in an amount up to the regulatory maximum amount for affiliated SBIC funds.

As of September 30, 2025, the SBIC debentures consisted of (i) $175.0 million par value of SBIC debentures issued by MSMF, with a recorded value of $170.8 million net of unamortized debt issuance costs of $4.2 million, and (ii) $175.0 million par value of SBIC debentures issued by MSC III, with a recorded value of $173.5 million net of unamortized debt issuance costs of $1.5 million.

May 2024 Notes

In May 2024, Main Street repaid the $450.0 million principal amount of the issued and outstanding 5.20% unsecured notes (the “May 2024 Notes”) at maturity at par value plus the accrued and unpaid interest.

December 2025 Notes

In September 2025, Main Street repaid the $100.0 million principal amount of the issued and outstanding 7.84% Series A unsecured notes (the “December 2025 Series A Notes”) and the $50.0 million principal amount of the issued and outstanding 7.53% Series B unsecured notes (the “December 2025 Series B Notes” and, together with the December 2025 Series A Notes, the “December 2025 Notes”) prior to maturity at par value plus the accrued and unpaid interest. The December 2025 Notes were due to mature on December 23, 2025.

NOTE F —FINANCIAL HIGHLIGHTS

The following is a schedule of financial highlights of Main Street for the nine months ended September 30, 2025 and 2024:

(1)Based on weighted-average number of common shares outstanding for the period.

(2)Net realized gains or losses, net unrealized appreciation or depreciation and related income tax provision or benefit can fluctuate significantly from period to period.

(3)MSCC’s taxable income for each period is an estimate and will not be finally determined until MSCC files its tax return for each year. As a result, the character of MSCC’s dividends and distributions for each period is also an estimate. Therefore, the final character of MSCC’s dividends and distributions may be different than this estimate.

(4)Includes the impact of the different share amounts as a result of calculating certain per share data based on the weighted-average basic shares outstanding during the period and certain per share data based on the shares outstanding as of a period end or transaction date.

(1)Total expenses are the sum of operating expenses and all tax expenses. The total tax provision or benefit includes the accrual of net deferred tax provision or benefit relating to book versus tax differences on income at the Taxable Subsidiaries that is included in net investment income, the net unrealized appreciation or depreciation on portfolio investments held in Taxable Subsidiaries and due to the change in the loss carryforwards, which are non-cash in nature and may vary significantly from period to period. Main Street is required to include net deferred tax provision or benefit in calculating its total expenses even though these net deferred taxes are not currently payable or receivable.

(2)Not annualized.

(3)Unless otherwise noted, operating expenses include interest, compensation, general and administrative and share-based compensation expenses, net of expenses allocated to the External Investment Manager of $17.0 million and $16.8 million for the nine months ended September 30, 2025 and 2024, respectively.

(4)Total investment return is based on the purchase of stock at the current market price on the first day and a sale at the current market price on the last day of each period reported on the table and assumes reinvestment of dividends at prices obtained by Main Street’s DRIP (as defined below) during the period. The return does not reflect any sales load that may be paid by an investor.

(5)Total return based on change in NAV was calculated using the sum of ending NAV plus dividends to stockholders and other non-operating changes during the period, divided by the beginning NAV. Non-operating changes include any items that affect NAV other than the net increase in net assets resulting from operations, such as the effects of stock offerings, shares issued under the DRIP and equity incentive plans and other miscellaneous items.

NOTE G —DIVIDENDS, DISTRIBUTIONS AND TAXABLE INCOME

Main Street currently pays regular monthly dividends to its stockholders and periodically pays supplemental dividends to its stockholders. Future dividends, if any, will be determined by its Board of Directors on a quarterly basis.

Summarized dividend information for the three and nine months ended September 30, 2025 and 2024 is as follows:

MSCC has elected to be treated for U.S. federal income tax purposes as a RIC. MSCC’s taxable income includes the taxable income generated by MSCC and certain of its subsidiaries, including the Funds and Structured Subsidiaries, which are treated as disregarded entities for tax purposes. As a RIC, MSCC generally will not pay corporate-level U.S. federal income taxes on any net ordinary taxable income or capital gains that MSCC distributes to its stockholders. MSCC must generally distribute at least 90% of its “investment company taxable income” (which is generally its net ordinary taxable income and realized net short-term capital gains in excess of realized net long-term capital losses) and 90% of its tax-exempt income to maintain its RIC status (pass-through tax treatment for amounts distributed). As part of maintaining RIC status, undistributed taxable income (subject to a 4% non-deductible U.S. federal excise tax) pertaining to a given fiscal year may be distributed up to twelve months subsequent to the end of that fiscal year, provided such dividends are declared on or prior to the later of (i) filing of the U.S. federal income tax return for the applicable fiscal year or (ii) the fifteenth day of the ninth month following the close of the year in which such taxable income was generated.

The determination of the tax attributes for Main Street’s distributions is made annually, based upon its taxable income for the full year and distributions paid for the full year. Therefore, a determination made on an interim basis may not be representative of the actual tax attributes of distributions for a full year. Ordinary dividend distributions from a RIC do not qualify for the 20% maximum tax rate (plus a 3.8% Medicare surtax, if applicable) on dividend income from domestic corporations and qualified foreign corporations, except to the extent that the RIC received the income in the form of qualifying dividends from domestic corporations and qualified foreign corporations. The tax attributes for distributions will generally include both ordinary income and qualified dividends, but may also include either one or both of capital gains and return of capital.

Listed below is a reconciliation of “Net increase in net assets resulting from operations” to taxable income and to total distributions declared to common stockholders for the nine months ended September 30, 2025 and 2024.

(1)MSCC’s taxable income for each period is an estimate and will not be finally determined until MSCC files its tax return for each year. Therefore, the final taxable income, and the taxable income earned in each period and carried forward for distribution in the following period, may be different than this estimate.

The Taxable Subsidiaries primarily hold certain equity investments for Main Street. The Taxable Subsidiaries permit Main Street to hold equity investments in portfolio companies which are “pass-through” entities for tax purposes and to continue to comply with the “source-of-income” requirements contained in the RIC tax provisions of the Code. The Taxable Subsidiaries are consolidated with MSCC for U.S. GAAP financial reporting purposes, and the portfolio investments held by the Taxable Subsidiaries are included in Main Street’s consolidated financial statements as portfolio investments and recorded at fair value. The Taxable Subsidiaries are not consolidated with MSCC for income tax purposes and may generate income tax expense, or benefit, and tax assets and liabilities, as a result of their ownership of certain portfolio investments. The taxable income, or loss, of the Taxable Subsidiaries may differ from their book income, or loss, due to temporary book and tax timing differences and permanent differences. The Taxable Subsidiaries are each taxed at corporate income tax rates based on their taxable income. The income tax expense, or benefit, if any, and the related tax assets and liabilities, of the Taxable Subsidiaries are reflected in Main Street’s consolidated financial statements.

The income tax provision for Main Street is generally composed of (i) deferred tax expense, which is primarily the result of the net activity relating to the portfolio investments held in the Taxable Subsidiaries, including changes in loss carryforwards, changes in net unrealized appreciation or depreciation and other temporary book tax differences, and (ii) current tax expense, which is primarily the result of current U.S. federal income and state taxes relating to net currently taxable activity relating to the portfolio investments held in the Taxable Subsidiaries and excise taxes on Main Street’s estimated undistributed taxable income. The income tax expense, or benefit, and the related tax assets and liabilities generated by the Taxable Subsidiaries, if any, are reflected in Main Street’s Consolidated Statements of Operations. Main Street’s provision for income taxes was comprised of the following for the three and nine months ended September 30, 2025 and 2024:

The net deferred tax liability as of September 30, 2025 and December 31, 2024 was $95.2 million and $86.1 million, respectively, with the change primarily related to changes in net unrealized appreciation or depreciation, changes in loss carryforwards and other temporary book-tax differences relating to portfolio investments held by the Taxable Subsidiaries. As of September 30, 2025, for U.S. federal income tax purposes, the Taxable Subsidiaries had a net operating loss carryforward which is not subject to expiration and will carryforward indefinitely until utilized. Additionally, the Taxable Subsidiaries have interest expense limitation carryforwards which have an indefinite carryforward period.

NOTE H —COMMON STOCK

Main Street maintains a program with certain selling agents through which it can sell shares of its common stock by means of at-the-market offerings from time to time (the “ATM Program”). During the nine months ended September 30, 2025, Main Street sold 390,990 shares of its common stock at a weighted-average price of $58.91 per share and raised $23.0 million of gross proceeds under the ATM Program. Net proceeds were $22.6 million after commissions to the selling agents on shares sold and offering costs. As of September 30, 2025, there wereno share sales transactions that had not settled. In March 2025, Main Street entered into new distribution agreements to sell up to 20,000,000 shares through the ATM Program. As of September 30, 2025,19,680,372 shares remained available for sale under the ATM Program.

During the year ended December 31, 2024, Main Street sold 2,489,275 shares of its common stock at a weighted-average price of $49.75 per share and raised $123.8 million of gross proceeds under the ATM Program. Net proceeds were $122.2 million after commissions to the selling agents on shares sold and offering costs.

NOTE I —DIVIDEND REINVESTMENT PLAN

The dividend reinvestment feature of Main Street’s dividend reinvestment and direct stock purchase plan (the “DRIP”) provides for the reinvestment of dividends on behalf of its stockholders, unless a stockholder has elected to receive dividends in cash. As a result, if Main Street declares a cash dividend, its stockholders who have not “opted out” of the DRIP by the dividend record date will have their cash dividend automatically reinvested into additional shares of Main Street common stock. The share requirements of the DRIP may be satisfied through the issuance of shares of common stock or through open market purchases of common stock by the DRIP plan administrator. Newly issued shares will be valued based upon the final closing price of Main Street’s common stock on the valuation date determined for each dividend by Main Street’s Board of Directors. Shares purchased in the open market to satisfy the DRIP requirements will be valued based upon the average price of the applicable shares purchased, before any associated brokerage or other costs. Main Street’s DRIP is administered by its transfer agent on behalf of Main Street’s record holders and participating brokerage firms. Brokerage firms and other financial intermediaries may decide not to participate in Main Street’s DRIP but may provide a similar dividend reinvestment plan for their clients.

Summarized DRIP information for the nine months ended September 30, 2025 and 2024 is as follows:

NOTE J —SHARE-BASED COMPENSATION

Main Street accounts for its share-based compensation plans using the fair value method, as prescribed by ASC 718, Compensation—Stock Compensation. Accordingly, for restricted stock awards (“RSAs”), Main Street measured the grant date fair value based upon the market price of its common stock on the date of the grant and amortizes the fair value of the awards as share-based compensation expense over the requisite service period, which is generally the vesting term.

Main Street’s Board of Directors approves the issuance of shares of restricted stock to Main Street employees pursuant to the Main Street Capital Corporation 2022 Equity and Incentive Plan (the “Equity and Incentive Plan”). These shares generally vest over athree-year orfive-year period from the grant date. The fair value is expensed over the service period, starting on the grant date. The following table summarizes the restricted stock issuances approved by Main Street’s Board of Directors under the Equity and Incentive Plan, net of shares forfeited, if any, and the remaining shares of restricted stock available for issuance as of September 30, 2025.

As of September 30, 2025, the following table summarizes the restricted stock issued to Main Street’s non-employee directors and the remaining shares of restricted stock available for issuance pursuant to the Main Street Capital Corporation 2022 Non-Employee Director Restricted Stock Plan. These shares are granted upon appointment or election to the board and vest on the day immediately preceding the annual meeting of stockholders following the respective grant date and are expensed over such service period.

For the three months ended September 30, 2025 and 2024, Main Street recognized total share-based compensation expense of $5.4 million and $4.9 million, respectively, related to the restricted stock issued to Main Street employees and non-employee directors. For the nine months ended September 30, 2025 and 2024, Main Street recognized total share-based compensation expense of $15.7 million and $13.9 million, respectively.

Summarized RSA activity for the nine months ended September 30, 2025 is as follows:

(1)Restricted units generally vest over athree-year orfive-year period from the grant date (as noted above).

(2)Vested shares included 177,090 shares withheld for payroll taxes paid on behalf of employees.

(3)Aggregate intrinsic value is the product of total non-vested restricted shares as of September 30, 2025 and $63.59 per share, the closing price of Main Street’s common stock on September 30, 2025.

As of September 30, 2025, there was $40.3 million of total unrecognized compensation expense related to Main Street’s non-vested restricted shares. This compensation expense is expected to be recognized over a remaining weighted-average period of 2.6 years as of September 30, 2025.

NOTE K —COMMITMENTS AND CONTINGENCIES

As of September 30, 2025, Main Street had the following outstanding commitments (in thousands):

(1)This table excludes commitments related tofour additional Other Portfolio investments for which the investment period has expired and remaining commitments may only be drawn to pay fund expenses. The Company does not expect any material future capital to be called on its commitment to these investments and as a result has excluded those commitments from this table.

(2)This table excludes commitments related tofive additional Other Portfolio investments for which the investment period has expired and remaining commitments may only be drawn to pay fund expenses or for follow-on investments in existing portfolio companies. The Company does not expect any material future capital to be called on its commitment to these investments to pay fund expenses, and based on representations from the fund manager, the Company does not expect any further capital will be called on its commitment for follow-on investments. As a result, the Company has excluded those commitments from this table.

Main Street will fund its unfunded commitments from the same sources it uses to fund its investment commitments that are funded at the time they are made (which are typically through existing cash and cash equivalents and borrowings under the Credit Facilities). Main Street follows a process to manage its liquidity and ensure that it has available capital to fund its unfunded commitments as necessary. The Company had no unrealized appreciation or depreciation on the outstanding unfunded commitments as of September 30, 2025.

Main Street may, from time to time, be involved in litigation arising out of its operations in the normal course of business or otherwise. Furthermore, third parties may seek to impose liability on Main Street in connection with the activities of its portfolio companies. While the outcome of any current legal proceedings cannot at this time be predicted with certainty, Main Street does not expect any current matters will materially affect its financial condition or results of operations; however, there can be no assurance whether any pending or future legal proceedings will have a material adverse effect on Main Street’s financial condition or results of operations in any future reporting period.

NOTE L —RELATED PARTY TRANSACTIONS

As discussed further in Note D — External Investment Manager, the External Investment Manager is treated as a wholly-owned portfolio company of Main Street and is included as part of Main Street’s Investment Portfolio. As of September 30, 2025, Main Street had a receivable of $10.3 million due from the External Investment Manager, which included (i) $7.2 million related primarily to operating expenses incurred by Main Street as required to support the External Investment Manager’s business and amounts due from the External Investment Manager to Main Street under a tax sharing agreement (see further discussion in Note D — External Investment Manager) and (ii) $3.1 million of dividends declared but not paid by the External Investment Manager. MSCC has entered into an agreement with the External Investment Manager to share employees in connection with its asset management business generally, and specifically for the External Investment Manager’s relationship with MSC Income and its other clients (see further discussion in Note A.1. — Organization and Basis of Presentation — Organization and Note D — External Investment Manager).

From time to time, Main Street may make investments in clients of the External Investment Manager in the form of debt or equity capital on terms approved by Main Street’s Board of Directors, including each director who is not an “interested person,” as such term is defined in Section 2(a)(19) of the 1940 Act.

Following the closing of the MSC Income’s follow-on public offering, Main Street entered into a share purchase plan to purchase up to $20.0 million in the aggregate of shares of MSC Income common stock in the open market for atwelve-month period beginning in March 2025, at times when the market price per share of MSC Income common stock is trading below the most recently reported NAV per share of MSC Income’s common stock by certain pre-determined levels (including any updates, corrections or adjustments publicly announced by MSC Income to any previously announced NAV per share). The purchases of shares of MSC Income common stock pursuant to the share purchase plan are intended to satisfy the conditions of Rule 10b5-1 and Rule 10b-18 under the Exchange Act and will otherwise be subject to applicable law, including Regulation M, which may prohibit purchases under certain circumstances. MSC Income also entered into a share repurchase plan to purchase up to $65.0 million in the aggregate of its common stock in the open market with terms and conditions substantially similar to Main Street’s share purchase plan for shares of MSC Income common stock, and daily purchases under thetwo plans, if any, are expected to be split pro rata (or as close thereto as reasonably possible) between Main Street and MSC Income based on the respective plan sizes. In connection with Main Street’s potential acquisition in excess of 3% of MSC Income’s outstanding shares of common stock as a result of any purchases pursuant to Main Street’s share purchase plan for shares of MSC Income common stock or otherwise, Main Street entered into a Fund of Funds Investment Agreement with MSC Income. The Fund of Funds Investment Agreement provides for the acquisition by Main Street of MSC Income’s shares of common stock, and MSC Income’s sale of such shares to Main Street, in a manner consistent with the requirements of Rule 12d1-4 under the 1940 Act.

The following table summarizes Main Street’s purchases of shares of MSC Income’s common stock during the three months ended September 30, 2025, pursuant to the share purchase plan.

(1)Includes broker commissions.

As of September 30, 2025, Main Street owned 1,433,573 shares of MSC Income’s common stock. Each of Main Street’s purchases of MSC Income common stock, either individually or through approval of the share purchase plan, was unanimously approved by the Board of Directors and MSC Income’s board of directors, including each director who is not an “interested person,” as such term is defined in Section 2(a)(19) of the 1940 Act, of each board. In addition, certain of Main Street’s officers and employees own shares of MSC Income and therefore have direct pecuniary interests in MSC Income.

In December 2020, the External Investment Manager entered into an investment management agreement with Private Loan Fund I to provide investment advisory and management services in exchange for an asset-based fee and certain incentive fees. Private Loan Fund I is a private investment fund exempt from registration under the 1940 Act that co-invests with Main Street in Main Street’s Private Loan investment strategy. In connection with Private Loan Fund I’s initial closing in December 2020, Main Street committed to contribute up to $10.0 million as a limited partner and is entitled to distributions on such interest. In February 2022, Main Street increased its total commitment to Private Loan Fund I from $10.0 million to $15.0 million. In addition, certain of Main Street’s officers and employees (and certain of their immediate family members) have made capital commitments to Private Loan Fund I as limited partners and therefore have direct pecuniary interests in Private Loan Fund I. As of September 30, 2025, Main Street has funded $14.2 million of its limited partner commitment and Main Street’s unfunded commitment was $0.8 million. Main Street’s limited partner commitment to Private Loan Fund I was unanimously approved by the Board of Directors, including each director who is not an “interested person,” as such term is defined in Section 2(a)(19) of the 1940 Act.

In March 2022, Main Street provided Private Loan Fund I with a revolving line of credit pursuant to a Secured Revolving Promissory Note, dated March 17, 2022 (as amended, the “PL Fund 2022 Note”), which provides for borrowings up to $15.0 million. Borrowings under the PL Fund 2022 Note bear interest at a rate of SOFR plus 3.0%, subject to a 2.0% SOFR floor, can be advanced through March 2026 and mature in March 2027. Available borrowings under the PL Fund 2022 Note are subject to a 0.25% non-use fee. The borrowings are collateralized by all assets of Private Loan Fund I (other than the assets of its special purpose vehicle financing subsidiary). The PL Fund 2022 Note was unanimously approved by Main Street’s Board of Directors, including each director who is not an “interested person,” as such term is defined in Section 2(a)(19) of the 1940 Act. As of September 30, 2025, there were $8.7 million of borrowings outstanding under the PL Fund 2022 Note.

In September 2023, the External Investment Manager entered into an investment management agreement with Private Loan Fund II to provide investment advisory and management services in exchange for an asset-based fee and certain incentive fees. Private Loan Fund II is a private investment fund exempt from registration under the 1940 Act that co-invests with Main Street in Main Street’s Private Loan investment strategy. In connection with Private Loan Fund II’s initial closing in September 2023, Main Street committed to contribute up to $15.0 million (limited to 20% of total commitments) as a limited partner and is entitled to distributions on such interest. In addition, certain of Main Street’s officers and employees (and certain of their immediate family members) have made capital commitments to Private Loan Fund II as limited partners and therefore have direct pecuniary interests in Private Loan Fund II. As of September 30, 2025, Main Street has funded $9.0 million of its limited partner commitment and Main Street’s unfunded commitment was $6.0 million. Main Street’s limited partner commitment to Private Loan Fund II was unanimously approved by the Board of Directors, including each director who is not an “interested person,” as such term is defined in Section 2(a)(19) of the 1940 Act.

In September 2023, Main Street provided Private Loan Fund II with a revolving line of credit pursuant to a Secured Revolving Promissory Note, dated September 5, 2023 (as amended, the “PL Fund II 2023 Note”), which provided for borrowings up to $50.0 million. Borrowings under the PL Fund II 2023 Note bore interest at a rate of SOFR plus 3.5%, subject to a 2.0% SOFR floor, and was scheduled to mature on September 5, 2025. Available borrowings under the PL Fund II 2023 Note were subject to a 0.25% non-use fee. The borrowings were collateralized by all assets of Private Loan Fund II. The PL Fund II 2023 Note was unanimously approved by Main Street’s Board of Directors, including each director who is not an “interested person,” as such term is defined in Section 2(a)(19) of the 1940 Act. In November 2024, Private Loan Fund II fully repaid all borrowings outstanding under the PL Fund II 2023 Note and the PL Fund II 2023 Note was extinguished.

In November 2024, Main Street provided Private Loan Fund II with a revolving line of credit pursuant to a Secured Revolving Promissory Note, dated November 22, 2024 (the “PL Fund II 2024 Note”), which provides for borrowings up to $10.0 million. Borrowings under the PL Fund II 2024 Note bear interest at a rate of SOFR plus 3.0%, subject to a 2.0% SOFR floor, and mature on the date upon which Private Loan Fund II’s investment period concludes, which is scheduled to occur in June 2029. Available borrowings under the PL Fund II 2024 Note are subject to a 0.25% non-use fee. The borrowings are collateralized by all assets of Private Loan Fund II (other than the assets of its special purpose vehicle financing subsidiary). The PL Fund II 2024 Note was unanimously approved by Main Street’s Board of Directors, including each director who is not an “interested person,” as such term is defined in Section 2(a)(19) of the 1940 Act. As of September 30, 2025, there wereno borrowings outstanding under the PL Fund II 2024 Note.

As described in Note B.9. — Summary of Significant Accounting Policies — Deferred Compensation Plan, participants in the Deferred Compensation Plan elect one or more investment options, including phantom Main Street stock units, interests in affiliated funds and various mutual funds, where their deferred amounts are notionally invested pending distribution pursuant to participant elections and plan terms. As of September 30, 2025, $32.1 million of directors’ fees and employee compensation, plus net unrealized gains and losses and investment income, and minus previous distributions, was deferred under the Deferred Compensation Plan. As of September 30, 2025, $12.5 million was deferred into phantom Main Street stock units, representing 196,761 shares of Main Street’s common stock. In addition, as of September 30, 2025, the Company had $19.6 million of funded investments from deferred compensation in trust, including $2.1 million in Private Loan Fund I and $4.5 million in Private Loan Fund II.

NOTE M —SUBSEQUENT EVENTS

The Company’s management has evaluated subsequent events through the date of issuance of the consolidated financial statements, and identified the following to report:

In November 2025, Main Street declared a supplemental dividend of $0.30 per share payable in December 2025. This supplemental dividend is in addition to the previously announced regular monthly dividends that Main Street declared of $0.255 per share for each month of October, November and December 2025, or total regular monthly dividends of $0.765 per share for the fourth quarter of 2025, resulting in total dividends declared for the fourth quarter of 2025 of $1.065 per share.

In November 2025, Main Street also declared regular monthly dividends of $0.26 per share for each month of January, February and March of 2026. These regular monthly dividends equal a total of $0.78 per share for the first quarter of 2026, representing a 4.0% increase from the regular monthly dividends paid in the first quarter of 2025. Including the regular monthly and supplemental dividends declared for the fourth quarter of 2025 and first quarter of 2026, Main Street will have paid $47.935 per share in cumulative dividends since its October 2007 initial public offering.

Consolidated Schedule of Investments in and Advances to Affiliates

(1)The principal amount, the ownership detail for equity investments and if the investment is income producing is included in the Consolidated Schedule of Investments included in Item 1. Consolidated Financial Statements of this Quarterly Report on Form 10-Q.

(2)Represents the total amount of interest, fees and dividends credited to income for the portion of the period for which an investment was included in Control or Affiliate categories, respectively. For investments transferred between Control and Affiliate categories during the period, any income or investment balances related to the time period it was in the category other than the one shown at period end is included in “Amounts related to investments transferred from other 1940 Act classifications during the period.”

(3)Gross additions include increases in the cost basis of investments resulting from new portfolio investments, follow-on investments and accrued PIK interest, and the exchange of one or more existing securities for one or more new securities. Gross additions also include net increases in unrealized appreciation or net decreases in net unrealized depreciation as well as the movement of an existing portfolio company into this category and out of a different category.

(4)Gross reductions include decreases in the cost basis of investments resulting from principal repayments or sales and the exchange of one or more existing securities for one or more new securities. Gross reductions also include net increases in net unrealized depreciation or net decreases in unrealized appreciation as well as the movement of an existing portfolio company out of this category and into a different category.

(5)Portfolio company located in the Midwest region as determined by location of the corporate headquarters. The fair value as of September 30, 2025 for Control investments located in this region was $589,459. This represented 20.1% of net assets as of September 30, 2025. The fair value as of September 30, 2025 for Affiliate investments located in this region was $181,094. This represented 6.2% of net assets as of September 30, 2025.

(6)Portfolio company located in the Northeast region and Canada as determined by location of the corporate headquarters. The fair value as of September 30, 2025 for Control investments located in this region was $158,589. This represented 5.4% of net assets as of September 30, 2025. The fair value as of September 30, 2025 for Affiliate investments located in this region was $125,926. This represented 4.3% of net assets as of September 30, 2025.

(7)Portfolio company located in the Southeast region as determined by location of the corporate headquarters. The fair value as of September 30, 2025 for Control investments located in this region was $72,101. This represented 2.5% of net assets as of September 30, 2025. The fair value as of September 30, 2025 for Affiliate investments located in this region was $270,957. This represented 9.2% of net assets as of September 30, 2025.

(8)Portfolio company located in the Southwest region as determined by location of the corporate headquarters. The fair value as of September 30, 2025 for Control investments located in this region was $1,043,897. This represented 35.6% of net assets as of September 30, 2025. The fair value as of September 30, 2025 for Affiliate investments located in this region was $187,380. This represented 6.4% of net assets as of September 30, 2025.

(9)Portfolio company located in the West region as determined by location of the corporate headquarters. The fair value as of September 30, 2025 for Control investments located in this region was $552,128. This represented 18.8% of net assets as of September 30, 2025. The fair value as of September 30, 2025 for Affiliate investments located in this region was $127,557. This represented 4.3% of net assets as of September 30, 2025.

(10)All of the Company’s portfolio investments are generally subject to restrictions on resale as “restricted securities,” unless otherwise noted.

(11)This schedule should be read in conjunction with the Consolidated Schedule of Investments and Notes to the Consolidated Financial Statements included in Item 1. Consolidated Financial Statements of this Quarterly Report on Form 10-Q. Supplemental information can be located within the Consolidated Schedule of Investments including end of period interest rate, preferred dividend rate, maturity date, investments not paid currently in cash and investments whose value was determined using significant unobservable inputs.

(12)Investment has an unfunded commitment as of September 30, 2025 (see Note K — Commitments and Contingencies). The fair value of the investment includes the impact of the fair value of any unfunded commitments.

(13)Negative fair value is the result of the capitalized discount being greater than the principal amount outstanding on the loan.

Consolidated Schedule of Investments in and Advances to Affiliates