Otter Tail Corp

1. Summary of Significant Accounting Policies

Overview

Otter Tail Corporation (OTC) and its subsidiaries (collectively, the "Company," "us," "our" or "we") form a diverse, multi-platform business consisting of a vertically integrated, regulated utility with generation, transmission and distribution facilities complemented by manufacturing businesses providing metal fabrication for custom machine parts and metal components, manufacturing of extruded and thermoformed plastic products, and manufacturing of PVC pipe products. We classify our business into three segments: Electric, Manufacturing and Plastics. Note 2 includes an additional description of the segments and financial information regarding each segment.

Principles of Consolidation

These consolidated financial statements are presented in accordance with U.S. generally accepted accounting principles and include the accounts of OTC and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation except, as applicable, profits on sales to our regulated electric utility company from our nonregulated businesses, which is in accordance with the accounting requirements of regulated operations.

Use of Estimates

We use estimates based on the best information available in recording transactions and balances resulting from business operations. As better information becomes available or actual amounts are known, the recorded estimates are revised. Consequently, operating results can be affected by revisions to prior accounting estimates.

Reclassifications

Short-term investments in the amount of $0.8 million were previously included in other current assets on our consolidated balance sheets as of December 31, 2024. This amount has been reclassified to maintain consistency and comparability between the periods presented and is now presented separately on the consolidated balance sheets. The reclassification had no impact on previously reported current or total assets, current or total liabilities, or total shareholders' equity.

Regulatory Accounting

Our regulated electric utility company, Otter Tail Power Company (OTP), is subject to regulation of rates and other matters by state utility commissions in Minnesota, North Dakota and South Dakota and by the FERC for certain interstate operations. OTP accounts for the financial effects of regulation in accordance with accounting guidance for regulated operations. This guidance allows for the recording of a regulatory asset for certain costs which otherwise would be recognized in the statements of income or comprehensive income based on an expectation that the cost will be recovered in future rates. This guidance also requires the recording of a regulatory liability for certain credits which would otherwise be recognized in the statements of income or comprehensive income based on an expectation that the amount will be returned to customers in future rates. Amounts recorded as regulatory assets and regulatory liabilities are generally recognized in the statements of income at the time they are reflected in customer rates. In the event OTP ceases to meet the criteria to apply the guidance for regulated operations, the regulatory assets and liabilities that no longer meet such criteria would be removed from the consolidated balance sheets and included in the consolidated statements of income as an expense or income item, or in the consolidated statements of comprehensive income as a loss or gain item, in the period in which the application of this guidance ceases.

Cash Equivalents

We consider all highly liquid investments purchased with maturity dates of 90 days or less to be cash equivalents.

Concentration of Deposits

We hold deposits with financial institutions which potentially subject us to a concentration risk. These deposits are guaranteed by the Federal Deposit Insurance Corporation up to an insurance limit of $250,000. Currently, our cash deposits exceed federally insured levels.

Revenue from Contracts with Customers

Due to our diverse business operations, the recognition of revenue from contracts with customers depends on the product produced and sold or service performed. We recognize revenue from contracts with customers at prices that are fixed or determinable as evidenced by an agreement with the customer, when we have met our performance obligation under the contract and it is probable that we will collect the amount to which we are entitled in exchange for the goods or services transferred or to be transferred to the customer. Depending on the product produced and sold or service performed and the terms of the agreement with the customer, we recognize revenue either over time, in the case of delivery or transmission of electricity or related services or the production and storage of certain custom-made products, or at a point in time for the delivery of standardized products and other products made to customer specifications where the terms of the contract require transfer of the completed product. Provisions for sales returns, early payment discounts and volume-based variable pricing incentives are recorded as reductions to revenue at the time revenue is recognized based on customer history, historical information and current trends. We include revenues received for shipping and handling in operating revenues. Expenses paid for shipping and handling are recorded as part of cost of products sold. Sales or other taxes collected from customers are excluded from operating revenues.

Electric Segment Revenues. Most Electric segment revenues are earned from the generation, transmission and sale of electricity to retail customers at rates approved by state regulatory commissions. OTP also earns revenue from the transmission of electricity for others over the transmission assets it owns separately or jointly with other transmission service providers, under rate tariffs established by the independent transmission system operator and approved by FERC. A third source of revenue for OTP comes from the generation and sale of electricity to wholesale customers at contract or market rates. Revenues from all these sources meet the criteria to be classified as revenue from contracts with customers and are recognized over time as energy is delivered or transmitted. Revenue is recognized based on the metered quantity of electricity delivered or transmitted at the applicable rates. For electricity delivered and consumed after a meter is read but not yet billed to a customer, OTP records revenue and an unbilled receivable based on estimates of the amount of energy delivered and a composite rate per kwh consumed.

Manufacturing Segment Revenues. Our Manufacturing segment businesses earn revenue predominantly from the production and delivery of custom-made or standardized parts and products to customers across several industries and from the production and sale of tools and dies to other manufacturers. For the production and delivery of standardized products and other products made to customer specifications where the terms of the contract require transfer of the completed product, we have met our performance obligation and recognize revenue at the point in time when the product is shipped. At this point we have no further obligation to provide services related to such products. The shipping terms used in these transactions are free on board (FOB) shipping point.

Plastics Segment Revenues. Our Plastics segment businesses earn revenue predominantly from the sale and delivery of standardized PVC pipe products produced at their manufacturing facilities. Revenue from the sale of these products is recognized at the point in time when the product is shipped as there is no further obligation to provide services related to such products and the shipping terms are FOB shipping point. We have one customer within our Plastics segment for which we produce and store a product made to the customer’s specifications and design under a build and hold agreement. For sales to this customer, we recognize revenue as the custom-made product is produced, adjusting the amount of revenue for volume rebate variable-pricing considerations we expect the customer will earn and applicable early payment discounts we expect the customer will take. Ownership of the pipe transfers to the customer prior to delivery and we are paid a negotiated fee for storage of the pipe. Revenue for storage of the pipe is recognized over time as the pipe is stored.

Alternative Revenue

In addition to recognizing revenue from contracts with customers, our Electric segment business also records revenue under alternative revenue program (ARP) requirements. Certain rate rider mechanisms qualify as ARP revenues as they provide for adjustments to rates outside of a general rate case proceeding to encourage or incentivize investments in certain areas such as conservation, renewable energy, pollution reduction or control, improved infrastructure of the transmission grid or other programs that provide benefits to the general public under public policy, laws or regulations. ARP riders generally provide for the recovery of specified costs and investments and include an incentive component to provide the regulated utility with a return on amounts invested.

We accrue ARP revenue on the basis of costs incurred, investments made and returns on those investments that qualify for recovery through established riders. ARP revenue is disclosed separately from revenue from contracts with customers and we have elected to report ARP revenue on a net basis, whereby amounts initially recorded as ARP revenue in a period are presented net of the reversal of amounts previously recognized as ARP revenue that are reclassified and recorded as revenue from contracts with customers when such amounts are included in the price of electricity to customers.

Receivables and Allowance for Credit Losses

We grant credit to our customers in the normal course of business with repayment terms generally ranging from 30 to 90 days after the invoice date. Late fees are assessed on certain receivables once they are 30 days past due. Unbilled receivables represent estimates of energy delivered to customers but not yet billed.

Receivables are stated at the billed or estimated unbilled amount less an allowance for estimated credit losses. An allowance for credit losses is established based on losses expected to occur over the contractual life of the receivable. We estimate an allowance for credit losses on our trade and unbilled receivables by evaluating historical aging and write-off history, adjusted for current and forecasted economic conditions, for groups of receivables that share similar economic characteristics. Other receivables are evaluated by reviewing individual accounts, considering aging, financial condition of the debtor, recent payment history and other relevant factors. Account balances are written off in the period they are deemed to be uncollectible.

Inventories

Inventories are valued at the lower of cost or net realizable value. Costs for fuel, material and supply inventories of our Electric segment are determined on an average-cost basis. Costs for raw material, work in process and finished goods inventories of our Manufacturing and Plastics segments are determined on a first-in, first-out (FIFO) basis.

Inventories consist of the following as of December 31, 2025 and 2024:

Investments

We invest in and hold, through rabbi trusts, corporate-owned life insurance policies to provide future funding for obligations under our supplemental pension plan and a nonqualified deferred compensation plan. The policies are recorded at cash surrender value and there are no restrictions on our ability to surrender the policies. Changes in the cash surrender value are recognized in earnings.

We hold debt, mutual fund and money market fund investments either as investments within our captive insurance entity, to provide future funding for obligations under nonqualified deferred compensation plans or provide a return on our available cash and liquidity. These investments are recorded at fair value.

Debt securities are deemed to be available-for-sale securities. We evaluate these securities for impairment at each reporting date. If the fair value of a security declines below its amortized cost, management assesses whether the decline is attributable to credit-related factors. Credit-related impairments are recognized as an allowance for expected credit losses with a corresponding charge to earnings. Non-credit related unrealized losses are recorded in accumulated other comprehensive income.

Unrealized gains and losses on mutual and money market funds are recognized in earnings.

Property, Plant and Equipment

Electric plant is stated at original cost less accumulated depreciation. The cost of additions includes purchased assets, contracted work, direct labor and materials, allocable overheads and allowance for funds used during construction (AFUDC). The amount of interest capitalized to electric plant was $1.5 million in 2025, $1.9 million in 2024 and $1.9 million in 2023. Significant additions or improvements that extend an asset's useful life are capitalized, while repairs and maintenance costs are expensed as incurred.

Depreciation is recognized on a straight-line basis over the asset's estimated useful life. Estimated useful lives generally range from five years to 80 years depending on the asset type. For certain asset classes, we employ a group or composite method of depreciation in which certain assets are combined and depreciated over the average life of the combined asset group. Actuarial studies are periodically performed to assess the remaining useful lives and salvage values of our assets, with any changes in these estimates incorporated into depreciation on a prospective basis. Gains or losses on group or composite asset dispositions are recorded to accumulated depreciation and impact current and future depreciation rates.

Amounts recovered in rates for future removal costs are recorded as regulatory liabilities. Removal costs, when incurred, are charged against the regulatory liability.

Property, plant and equipment of our nonelectric operations are carried at historical cost less accumulated depreciation. Depreciation is recognized on a straight-line basis over the asset's estimated useful life. Estimated useful lives generally range from two years to 40 years depending on the asset type. The cost of additions includes purchased assets, contracted work, direct labor and materials, allocable overheads and capitalized interest, as applicable. No interest was capitalized in 2025, 2024 or 2023. Maintenance and repairs are expensed as incurred. Gains or losses on asset dispositions are included in the determination of operating income.

Jointly Owned Facilities

OTP is a joint owner intwo coal-fired steam-powered electric generation plants: Big Stone Plant near Big Stone City, South Dakota and Coyote Station near Beulah, North Dakota. OTP is also a joint owner, with other regional utilities, in several major transmission lines. OTP's interest in each jointly owned facility is reflected in the consolidated balance sheets on a pro-rata basis and OTP's share of direct revenue and expenses are included in operating revenues and expenses in the consolidated statements of income. Each participant in the jointly owned facilities finances their own investments.

Goodwill and Other Intangible Assets

Goodwill is recognized and initially measured as any excess of the acquisition-date consideration transferred in a business combination over amounts recognized for the net identifiable assets acquired. Goodwill is not amortized, but is tested for impairment annually, or more frequently if an event occurs or circumstances change that would more likely than not result in an impairment of goodwill. Impairment testing is performed at the reporting unit level, which is defined as an operating segment or one level below an operating segment. We perform our impairment testing in the fourth quarter of each year and have identified three reporting units that carry a goodwill balance.

We perform a quantitative impairment assessment, electing to forgo the optional qualitative assessment. The quantitative assessment is a single-step test that identifies both the existence of impairment and the amount of impairment loss by comparing the estimated fair value of a reporting unit to its carrying value, with any excess carrying value over the fair value being recognized as an impairment loss.

Intangible assets with finite lives, which primarily consist of customer relationships, are carried at estimated fair value at the time of acquisition less accumulated amortization. The costs of the intangible assets are amortized over their estimated useful lives, which generally range from 15 to 20 years.

Cloud Computing Costs

We capitalize implementation costs incurred in cloud computing arrangements that are service contracts consistent with capitalized implementation costs incurred to develop or obtain internal-use software. Costs are amortized on a straight-line basis over the life of the associated contract. Capitalized implementation costs are amortized over periods up toten years. Capitalized costs and related accumulated amortization are included in other noncurrent assets on the consolidated balance sheets. Below are the amounts of capitalized cost and related accumulated amortization as of December 31, 2025 and 2024:

Amortization expense of capitalized implementation costs for each of the years ended December 31, 2025, 2024 and 2023 totaled $4.3 million, $3.0 million, and $1.3 million.

Leases

We recognize a right-of-use lease asset and a corresponding lease liability at the lease commencement date for all long-term leases. The length of our lease agreements varies from less thanone year to approximatelyten years. We have elected to not record lease assets and liabilities for leases with a lease term at commencement of 12 months or less; such leases are expensed on a straight-line basis over the lease term. Certain of our leases contain options to renew or extend the lease term at our discretion if certain conditions are met. If a lease contains an option to extend the lease term and there is reasonable certainty the option will be exercised, the option is considered in the lease term at inception, or at such time when an event occurs which triggers the remeasurement of the lease, as applicable. In the determination of the lease term for one of our leased manufacturing facilities, we have incorporated the future lease renewals which we believe are reasonably certain to be exercised in the associated right-of-use asset and liability values.

We have elected to not separate non-lease components (e.g., common area maintenance) from lease components on real estate leases, accordingly the recognized lease asset and lease liability incorporate in their measurement payments for non-lease components. Certain leases include variable lease payments as the amounts are subject to change over the lease term; such amounts are not incorporated into the measurement of the right-of-use lease asset or lease liability. We are unable to determine the interest rate implicit in our leases, thus we apply our incremental borrowing rate to capitalize the right-of-use asset and lease liability. We estimate our incremental borrowing rate by reference to market interest rates on long-term debt, incorporating considerations of the credit quality of the lessee and the term of lease.

Recoverability of Long-Lived Assets

We review our long-lived assets including, among other assets, property, plant and equipment, amortizing intangible assets and right-of-use lease assets whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. We determine potential impairment by comparing the carrying amount of the assets with the net cash flows expected to be provided by operating activities of the business or related assets. If the sum of the expected future net cash flows is less than the carrying amount of the assets, an impairment loss would be recognized. Such an impairment loss would be measured as the amount by which the carrying amount exceeds the fair value of the asset.

Pension Plans and Other Postretirement Benefits

We maintain pension and postretirement benefit plans for eligible employees. Recognizing the cost of providing benefits and measuring the projected benefit obligations of these plans requires management to make various assumptions and estimates. Certain unrecognized actuarial gains and losses and unrecognized prior service costs or credits are deferred as regulatory assets and liabilities, rather than recorded as other comprehensive income, based on regulatory recovery mechanisms.

We have elected to apply a minimum amortization method for determining the amount of amortization of net cumulative gains or losses to be included as a component of net periodic benefit cost for any annual period. Cumulative gains and losses recognized in accumulated other comprehensive income or as a deferred regulatory asset or liability that are in excess of 10% of the projected benefit obligation or, where applicable, the market value of pension plan assets are amortized over the expected remaining future service period of active plan participants. In periods in which the cumulative gains and losses do not exceed 10%, no amortization to net periodic benefit cost is recognized.

Asset Retirement Obligations

Legal obligations related to the future retirement of long-lived assets are recognized as asset retirement obligations (ARO). An ARO is recognized in the period in which the legal obligation is incurred and the amount of the obligation can be reasonably estimated, with an offsetting increase to the associated long-lived asset. AROs are initially recognized at fair value and increased with the passage of time (accretion). ARO estimates are revised periodically with any adjustments reflected in the ARO and associated long-lived asset.

Income Taxes

We use the asset and liability method to account for income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of all temporary differences between the carrying amounts of assets and liabilities and their respective tax bases. Deferred taxes are recorded using the tax rates scheduled by tax law to be in effect in the periods when the temporary differences reverse. Deferred tax assets are reduced by a valuation allowance when it is more likely than not that a portion or all of the deferred tax assets will not be realized. The realizability of deferred tax assets is determined by taking into consideration forecasts of future taxable income, the reversal of other existing temporary differences, available net operating loss carryforwards and available tax planning strategies. Changes in valuation allowances are included in the provision for income taxes in the period of the changes.

We recognize the tax effects of all tax positions that are more-likely-than-not to be sustained on audit based solely on the technical merits of those positions as of the balance sheet date. Changes in the recognition or measurement of such positions are recognized in the provision for income taxes in the period of the changes. We classify interest and penalties on tax uncertainties as components of the provision for income taxes within the consolidated statements of income.

We have elected to account for transferable tax credits as a component of our income tax provision. We recognize the benefit of PTCs as a reduction of income tax expense in the period the credit is generated, which corresponds to the period the energy production occurs. We apply the deferral method of accounting for ITCs and state wind energy credits. Under this method, ITCs and state wind energy credits are amortized as a reduction to income tax expense over the estimated useful lives of the underlying property that gave rise to the credit.

Deferred Compensation Plans

The Company sponsorstwo nonqualified deferred compensation plans for the benefit of executive officers and other select employees. Each plan allows participants to defer a specified amount or percentage of base wages or incentive compensation into the plan, subject to certain limitations. The Company, at its discretion, may make employer contributions to either plan during any annual period. Participant and employer deferred amounts are segregated into one or more accounts chosen by the participant. Participants earn a return on deferred amounts based on notional investments in the segregated accounts. Participants can elect lump sum distributions or annual installments of deferred balances during the participant's employment or upon retirement. As of December 31, 2025 and 2024, our liability to participants under these deferred compensation plans was $35.0 million and $29.1 million. Company contributions to these plans were $1.0 million, $1.3 million and $1.2 million for the years ended December 31, 2025, 2024 and 2023. Expenses recognized due to changes in our payment obligations in connection with these plans amounted to $3.9 million, $3.3 million and $3.3 million for the years ended December 31, 2025, 2024 and 2023.

Stock-Based Compensation

Stock-based compensation awards are measured at the grant-date fair value of the award and compensation expense is recognized on a straight-line basis over the applicable service or performance period. The service period may be limited to the period until such time that a recipient is retirement eligible as determined under the award agreement. Awards granted to employees eligible for retirement on the date of grant are expensed in the period of grant. We recognize the effects of award forfeitures as they occur.

Fair Value Measurements

Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants. Three levels of inputs may be used to measure fair value:

Level 1 – Quoted prices are available in active markets for identical assets or liabilities as of the reported date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices, such as equities listed on the New York Stock Exchange and commodity derivative contracts listed on the New York Mercantile Exchange.

Level 2 – Pricing inputs are other than quoted prices in active markets but are either directly or indirectly observable as of the reported date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, such as treasury securities with pricing interpolated from recent trades of similar securities, or priced with models using highly observable inputs, such as commodity options priced using observable forward prices and volatilities.

Level 3 – Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those with inputs requiring significant management judgment or estimation and may include complex and subjective models and forecasts.

In instances where the determination of the fair value measurement is based on inputs from different levels within the hierarchy, the level in the hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety.

Related Parties

The Otter Tail Corporation Foundation and Otter Tail Power Company Foundation are independent not-for-profit charitable entities affiliated with the Company and are not included in OTC's consolidated financial statements. Contribution obligations to thetwo foundations totaling $4.5 million and $5.5 million were recognized as of December 31, 2025 and 2024. Cash contributions paid to thetwo foundations during the years ended December 31, 2025, 2024 and 2023 were $5.5 million, $5.5 million, and $4.3 million.

Variable Interest Entity

The co-owners of Coyote Station, including OTP, are party to a Lignite Sales Agreement (LSA) with Coyote Creek Mining Company, LLC (CCMC), a subsidiary of The North American Coal Corporation. The agreement provides for the purchase of lignite coal to meet the coal supply requirements of Coyote Station through December 2040. The price per ton paid by the Coyote Station owners under the LSA reflects the cost of production, along with an agreed-upon profit and capital charge. CCMC was formed for the purpose of mining coal to meet the coal fuel supply requirements of Coyote Station and, based on the terms of the LSA, is considered a variable interest entity (VIE) due to the transfer of all operating and economic risk to the Coyote Station owners, as the agreement is structured so that the price of the coal would cover all costs of operations as well as future reclamation costs. The Coyote Station owners are required to buy certain assets of CCMC at book value should they terminate the contract prior to the end of the contract term and are providing a guarantee of the value of the equity of CCMC because the Coyote Station owners are required to buy the membership interests of CCMC at the end of the contract term at equity value. Under current accounting standards, the primary beneficiary of a VIE is required to include the assets, liabilities, results of operations and cash flows of the VIE in its consolidated financial statements. No single owner of Coyote Station owns a majority interest in Coyote Station and none, individually, has the power to direct the activities that most significantly impact CCMC. Therefore, none of the owners individually, including OTP, is considered the primary beneficiary of the VIE and the Company is not required to include CCMC in its consolidated financial statements.

If the LSA terminates prior to the expiration of its term or the production period terminates prior to December 31, 2040 and the Coyote Station owners purchase all of the outstanding membership interests of CCMC, the owners will satisfy or, if permitted by CCMC’s applicable lenders, assume all of CCMC’s obligations owed to CCMC’s lenders under its loans and leases. The Coyote Station owners have limited rights to assign their rights and obligations under the LSA without the consent of CCMC’s lenders during any period in which CCMC’s obligations to its lenders remain outstanding. In the event the contract is terminated prior to the end of the term due to certain events, OTP’s maximum loss exposure, as a result of its involvement with CCMC, could be as high as $35 million, or OTP’s 35% share of CCMC’s unrecovered costs as of December 31, 2025.

Recently Adopted Accounting Pronouncements

Income Taxes. In December 2023, the FASB issued amended authoritative guidance codified in Accounting Standards Codification (ASC) 740, Income Taxes. The amended guidance requires additional disaggregated information in effective tax rate reconciliation disclosures and additional disaggregated information about income taxes paid. We adopted this updated standard for the year ended December 31, 2025, on a retrospective basis and applied the new disclosure requirements. Accordingly, prior periods in our effective tax rate reconciliation disclosures in Note 13 have been reclassified to conform to the current year presentation. The adoption of this updated standard resulted in additional and modified disclosures related to our income tax expenses and income taxes paid. The adoption of this updated standard did not have an impact on our consolidated financial position or operating results.

Recent Accounting Pronouncements

Disaggregated Income Statement Expenses. In November 2024, the FASB issued authoritative guidance codified in ASC 220, Income Statement—Reporting Comprehensive Income, which will require additional disclosure of certain costs and expenses within the notes to the financial statements. The new standard is effective for our annual periods beginning in 2027 and interim periods beginning in the first quarter of fiscal 2028 and can be applied on either a prospective or retrospective basis. Early adoption of the new standard is permitted. We anticipate adopting the updated standard in our Form 10-K for the year ending December 31, 2027.

Software Costs. In September 2025, the FASB issued amended authoritative guidance codified in ASC 350, Intangibles – Goodwill and Other. The amended guidance updates the cost capitalization threshold for internal-use software development costs by removing all references to software project development stages and providing new guidance on how to evaluate whether the probable-to-complete recognition threshold has been met. The updated standard is effective for our annual and interim periods beginning in 2028. Early adoption of the amended guidance is permitted. The amended guidance can be applied on a prospective, modified, or retrospective basis. We are currently evaluating the impact that the updated standard will have on our consolidated financial statements, but we do not anticipate it will have a material effect on our future financial position or operating results.

Government Grants. In December 2025, the FASB issued authoritative guidance codified in ASC 832, Government Grants, which adds guidance on the recognition, measurement and presentation of government grants. The new guidance is effective for our annual periods beginning in 2029, including interim periods within that fiscal year, and can be applied on a modified prospective, modified retrospective, or full retrospective basis. We are currently evaluating the impact of this guidance on our consolidated financial statements and related disclosures.

2. Segment Information

Our business is comprised ofthree reportable segments, Electric, Manufacturing and Plastics, consistent with our business strategy, organizational structure and our internal reporting and review processes. Our chief operating decision maker (CODM) is our Chief Executive Officer. Segment net income is the sole measure of segment profit or loss used by our CODM in assessing segment performance and allocating resources to our segments. Our CODM uses segment net income in assessing financial performance on a monthly basis, reviewing and approving annual operating budgets and periodic forecasts, allocating capital or financial resources to our segments, making strategic decisions and measuring returns on equity in comparison to internal thresholds or peer entities.

The operations of ourthree reportable segments are further described below. We have aggregatedtwo operating segments within our Manufacturing reportable segment based on the similarity between these businesses and their economic characteristics.

Electric includes our vertically integrated regulated utility engaged in the production, transmission, distribution and sale of electric energy in western Minnesota, eastern North Dakota and northeastern South Dakota.

Manufacturing consists of businesses which provide metal fabrication services for custom machine parts and metal components and manufacture thermoformed plastic products for use in the agriculture, construction, horticulture, industrial, lawn and garden, recreational vehicle (powersports) and other end markets. These businesses have manufacturing facilities in Georgia, Illinois and Minnesota and sell products primarily in the United States.

Plastics consists of businesses producing PVC pipe at plants in North Dakota and Arizona. Our PVC pipe is sold primarily in the western half of the United States and Canada and is generally used in municipal water infrastructure, which encompasses potable water distribution, wastewater collection and distribution and water reclamation systems. Our PVC pipe is also used within residential and commercial structures and rural water systems.

Segment Profit or Loss

Information about each segment, including significant expenses and net income of each segment, for the years ended December 31, 2025, 2024 and 2023 are as follows:

Electric Segment

Manufacturing Segment

Plastics Segment

Capital Expenditures and Identifiable Assets

The following provides capital expenditures for each reportable segment and our corporate cost center for the years ended December 31, 2025, 2024 and 2023:

The following provides the identifiable assets by segment and corporate assets as of December 31, 2025 and 2024:

Corporate assets consist primarily of cash and cash equivalents, investments, fixed assets, and prepaid expenses.

Reconciliation to Consolidated Amounts

Certain costs are not allocated to our operating segments. Corporate operating costs include items such as corporate staff and overhead costs, the results of our captive insurance company and other items excluded from the measurement of operating segment performance. Corporate is not an operating segment, rather it is added to operating segment totals to reconcile to consolidated amounts.

Included below is a reconciliation of certain segment information and our unallocated corporate costs to consolidated amounts for the years ended December 31, 2025, 2024 and 2023:

Concentrations

Our Plastics segment businesses use PVC resin as a critical component within their PVC pipe manufacturing process. The domestic PVC resin industry is highly consolidated, with only four resin suppliers in the U.S. We rely on these four suppliers to source our PVC resin requirements. Additionally, most U.S. resin production plants are located in the Gulf Coast region. These plants are subject to the risk of damage and production shutdowns because of exposure to hurricanes or other extreme weather events that occur in this region. The loss of a key vendor, or any interruption or delay in the supply of PVC resin could cause production delays, a possible loss of sales or result in increased costs to secure resin, all of which would adversely affect our operating results.

For the year ended December 31, 2025, two customers combined to account for 16% of Electric segment operating revenues, three customers combined to account for 44% of Manufacturing segment operating revenues and two customers combined to account for 47% of Plastics segment operating revenues. However, no individual customer provided 10% or more of our consolidated operating revenues.

Entity-Wide Information

All of our long-lived assets are located within the United States and substantially all of our operating revenues are from customers located within the United States.

3. Revenue

Presented below are our operating revenues from external customers, in total and by amounts arising from contracts with customers and ARP arrangements, disaggregated by revenue source and segment for the years ended December 31, 2025, 2024 and 2023:

4. Receivables

Receivables as of December 31, 2025 and 2024 are as follows:

The following is a summary of activity in the allowance for credit losses for the years ended December 31, 2025 and 2024:

5. Investments

The following is a summary of our investments as of December 31, 2025 and 2024:

As of December 31, 2025, our government and corporate debt securities had maturity dates ranging from June 2026 to July 2035.

During the years ended December 31, 2025, 2024 and 2023, our investment income, which consisted primarily of interest on our cash equivalent and debt security investments, and gains on our corporate-owned life insurance policy investments, totaled $22.2 million, $19.8 million, and $15.2 million, which is included in other income in our consolidated statements of income.

Debt Securities

The following table summarizes the amortized cost and fair value of debt securities available for sale and the corresponding amounts of gross unrealized gains and losses as of December 31, 2025 and 2024:

As of December 31, 2025 and 2024, no unrealized losses on debt securities were deemed to be credit-related.

The following table summarizes the fair value of debt securities available for sale by contractual maturity date as of December 31, 2025:

Equity Securities

The amount of net unrealized gains and losses during the years ended December 31, 2025 and 2024 on marketable equity securities still held as of December 31, 2025 and 2024 was not material.

6. Regulatory Matters

Regulatory Assets and Liabilities

The following presents our current and long-term regulatory assets and liabilities as of December 31, 2025 and 2024 and the period we expect to recover or refund such amounts:

Pension and Other Postretirement Benefit Plans represent benefit costs and actuarial losses and gains subject to recovery or refund through rates as they are expensed or amortized. These unrecognized benefit costs and actuarial losses and gains are eligible for treatment as regulatory assets or liabilities based on their probable inclusion in future electric rates.

Alternative Revenue Program Riders regulatory assets and liabilities are revenues not yet collected from customers or amounts collected from customers that are subject to refund, respectively, primarily due to investments in qualifying transmission, conservation, renewable resource, environmental and other generation assets, and the impact of decoupling.

Deferred Income Taxes primarily represent the revaluation of accumulated deferred income taxes arising from the change in the federal income tax rate in 2017. This amount is being refunded to customers over the estimated lives of the property assets from which the deferred income taxes originated.

Fuel Clause Adjustments represent the under- or over-collection of fuel costs relative to the estimated cost of fuel included in customer rates, which will be collected from or returned to customers in future periods.

Derivative Instruments represent unrealized losses recognized on derivative instruments. On final settlement of such instruments, any realized losses are recovered from customers.

Plant Removal Obligations represent amounts collected from customers to be used to cover actual removal costs as incurred.

North Dakota PTC Refunds represent PTCs earned from our wind energy facilities. These amounts are being allocated to customers over the lives of the assets generating the credits.

Other regulatory assets and liabilities include other amounts that we expect to recover from or return to customers in future periods, such as the cost of abandoned projects, costs incurred in connection with recent rate cases and other items.

North Dakota Rate Case

On December 30, 2024, the NDPSC approved a settlement agreement between OTP and certain interested parties in their general rate case and issued its written order on final rates. The key provisions of the order include a revenue requirement of $225.6 million, based on a return on rate base of 7.53%, and an allowed ROE of 10.10% on an equity ratio of 53.50%. The net annual revenue requirement includes a net increase of $13.1 million or 6.18%. Through the settlement of the case, the parties also agreed to establish an earnings-sharing mechanism, whereby 70% of actual earnings in excess of a 10.20% ROE would be returned to customers, with OTP retaining the remaining 30%. New base rates in North Dakota went into effect on March 15, 2025.

South Dakota Rate Case

On June 4, 2025, OTP filed a request with the SDPUC for an increase in revenue recoverable under general rates in South Dakota. In its filing, OTP requested a net increase in annual revenue of $5.7 million, or 12.50%, based on an allowed rate of return on rate base of 8.29% and an allowed ROE of 10.80% on an equity ratio of 53.54% of total capital. Through this proceeding, OTP has proposed changes to the mechanism of certain cost and investment recovery, with recovery moving from riders into base rates. Interim rates went into effect on December 1, 2025 and are subject to potential refund until the finalization of the rate case.

Minnesota Rate Case

On October 31, 2025, OTP filed a request with the MPUC for an increase in revenue recoverable under general rates in Minnesota. In its filing, OTP requested a net increase in annual revenue of $44.8 million, or 17.7%, based on an allowed rate of return on rate base of 7.92% and an allowed ROE of 10.65% on an equity ratio of 53.5% of total capital. The request includes, among other items, accelerated recovery of the remaining investment of the jurisdictionally allocated share of Coyote Station, which has a $4.3 million annual impact. The request for accelerated recovery is driven by the MPUC’s order in OTP’s most recent IRP to discontinue serving Minnesota customers with capacity and energy from Coyote Station by December 2031. If this part of the request is granted, we anticipate the amounts collected would be deferred and recognized over the remaining estimated useful life of the plant, which extends until 2041. The filing also included an interim rate request for a net increase in annual revenue of $31.8 million, or 12.6%.

On December 23, 2025, the MPUC approved the interim rate request with a modification to exclude the impact of the accelerated recovery of the remaining investment of the jurisdictionally allocated share of Coyote Station from interim rates. The resulting interim net increase in annual revenue is $28.6 million, or 11.3%. Interim rates went into effect on January 1, 2026, and are subject to potential refund until the finalization of the rate case.

7. Property, Plant and Equipment

Major classes of property, plant and equipment as of December 31, 2025 and 2024 include:

Depreciation expense for the years ended December 31, 2025, 2024 and 2023 totaled $116.0 million, $99.4 million and $90.8 million.

The following table provides OTP’s ownership percentages and amounts included in the December 31, 2025 and 2024 consolidated balance sheets for OTP’s share of each of these jointly owned facilities:

8. Intangible Assets

The following table summarizes our goodwill by segment as of December 31, 2025 and 2024:

Our annual goodwill impairment testing, performed in the fourth quarter of 2025 and 2024, indicated no impairment existed as of the test date.

The following table summarizes the components of our intangible assets as of December 31, 2025 and 2024:

Amortization expense for these intangible assets for each of the years ended December 31, 2025, 2024 and 2023 was $1.1 million each year.

Annual amortization expense for these intangible assets for the next five years is:

9. Leases

We lease rail cars, warehouse and office space, land, and certain office, manufacturing, material handling and other equipment under varying terms and conditions. All leases are classified as operating leases.

The components of lease cost and lease cash flows for the years ended December 31, 2025, 2024, and 2023 are as follows:

A summary of operating lease right-of-use lease assets and lease liabilities as of December 31, 2025 and 2024 is as follows:

Operating lease assets obtained in exchange for new operating lease liabilities amounted to $3.6 million and $17.6 million for the years ended December 31, 2025 and 2024.

Maturities of lease liabilities as of December 31, 2025 for each of the next five years and in the aggregate thereafter are as follows:

The weighted-average remaining lease term and the weighted-average discount rate as of December 31, 2025 and 2024 are as follows:

10. Short-Term and Long-Term Borrowings

The following is a summary of our outstanding short- and long-term borrowings by borrower, OTC or OTP, as of December 31, 2025 and 2024:

Short-Term Debt

The following is a summary of our lines of credit as of December 31, 2025 and 2024:

OTC and OTP are each party to separate credit agreements (the OTC Credit Agreement and OTP Credit Agreement, respectively). The OTC Credit Agreement provides for a $170.0 million unsecured revolving line of credit, and the OTP Credit Agreement provides for a $220.0 million unsecured revolving line of credit. Both credit facilities are to support operations, fund capital expenditures, refinance certain indebtedness and provide for the issuance of letters of credit in an aggregate amount not to exceed $40.0 million under the OTC Credit Agreement and $50.0 million under the OTP Credit Agreement. Each credit facility includes an accordion provision allowing the borrower to increase the borrowing capacity under the facility, subject to certain conditions, up to $290.0 million and $300.0 million under the OTC Credit Agreement and OTP Credit Agreement, respectively.

Borrowings under each credit facility are subject to a variable rate of interest on outstanding balances and a commitment fee is charged based on the average unused amount available to be drawn under the respective facility. The variable rate of interest to be charged is based on a benchmark interest rate, either SOFR or a Base Rate, as defined in the credit agreements, selected by the borrower at the time of an advance, subject to the conditions of each agreement, plus an applicable credit spread. The credit spread ranges from zero to 2.00%, depending on the benchmark interest rate selected, and is subject to adjustment based on the credit ratings of the relevant borrower. The weighted-average interest rate on all outstanding borrowings as of December 31, 2025 and 2024 was 5.08% and 5.61%.

Each credit facility contains a number of restrictions on the borrower, including restrictions on the ability to merge, sell assets, make investments, create or incur liens on assets, guarantee the obligations of any other party and engage in transactions with related parties. The agreements also require the borrower to maintain various financial covenants, as further described below. Each credit facility includes a cross-default provision whereby an event of default of other outstanding indebtedness will trigger an event of default under the agreement.

The terms of each credit facility include a provision for the borrower to request, and the lenders to grant an extension of the maturity date of the facility by one year, subject to certain terms and conditions. In 2025, a one-year extension was granted, and the current maturity date of each facility is December 11, 2030.

Long-Term Debt

The following is a summary of outstanding long-term debt by borrower as of December 31, 2025 and 2024:

On March 27, 2025, OTP entered into a Note Purchase Agreement pursuant to which OTP issued, in a private placement transaction, $100.0 million of senior unsecured notes consisting of (a) $50.0 million of 5.49% Series 2025A Senior Unsecured Notes due March 27, 2035, and (b) $50.0 million of 5.98% Series 2025B Senior Unsecured Notes due June 5, 2055. The Series 2025A Notes were issued on March 27, 2025, upon entering into the agreement. The Series 2025B Notes were issued on June 5, 2025.

Per the terms of the agreement, OTP may prepay all or any part of the notes (in an amount not less than 10% of the aggregate principal amount of the notes then outstanding in the case of a partial prepayment) at 100% of the principal amount so prepaid, together with unpaid accrued interest and a make-whole amount, as defined in the agreement; provided that no default or event of default exists under the agreement. Any prepayment of the Series 2025A Notes then outstanding on or after December 27, 2034, or the Series 2025B Notes then outstanding on or after December 5, 2054, will be made without any make-whole amount. Consistent with other of our borrowings, the agreement contains a number of restrictions on the business of OTP, including restrictions on OTP’s ability to merge, sell substantially all assets, create or incur liens on assets, guarantee the obligations of any other party, and engage in certain transactions with affiliates.

Our guaranteed and unsecured notes require the borrower to maintain various financial covenants, as further described below. These notes provide for prepayment options allowing for a full or partial prepayment at 100% of the principal amount so prepaid, together with unpaid accrued interest and a make-whole amount, as defined. These notes also include restrictions on the borrower, including its ability to merge, sell assets, create or incur liens on assets, guarantee the obligations of any other party and engage in transactions with related parties. The notes include a cross-default provision whereby an event of default of other outstanding indebtedness will trigger an event of default under the note.

Aggregate maturities of long-term debt obligations on December 31, 2025 for each of the next five years are as follows:

Financial Covenants

Certain of OTC's and OTP's short-term and long-term debt agreements require the borrower, whether OTC or OTP, to maintain certain financial covenants, including a maximum debt to total capitalization of either 0.60 to 1.00 or 0.65 to 1.00, depending on the debt agreement, a minimum interest and dividend coverage ratio of 1.50 to 1.00, and a maximum level of priority indebtedness. As of December 31, 2025, OTC and OTP were in compliance with these financial covenants.

Guaranties

OTC's obligations under the terms of its Guaranteed Senior Notes are unconditionally and irrevocably guaranteed by its subsidiaries, Varistar Corporation, BTD Manufacturing, Inc., Northern Pipe Products, Inc. and Vinyltech Corporation.

11. Employee Postretirement Benefits

Pension Plan and Other Postretirement Benefits

The Company sponsors a noncontributory funded pension plan (the Pension Plan), an unfunded, nonqualified Executive Survivor and Supplemental Retirement Plan (ESSRP), both accounted for as defined benefit pension plans, and a postretirement healthcare plan accounted for as an other postretirement benefit plan.

The Pension Plan, which previously covered substantially all corporate and OTP employees, was closed to new employees in 2013. The plan provides retirement compensation to all covered employees at age 65, with reduced compensation in cases of retirement prior to age 62. Participants are fully vested after completing five years of vesting service. The plan assets consist of equity funds, fixed income funds, cash and cash equivalents and alternative investments. None of the plan assets are invested in common stock or debt securities of the Company.

The ESSRP, an unfunded plan, provides for defined benefit payments to executive officers and certain key management employees on their retirement for life, or to their beneficiaries on their death. The ESSRP was amended and restated in 2019 to i) freeze the participation in the restoration retirement benefit component of the plan and ii) freeze benefit accruals under the restoration retirement benefit component of the plan for all participants of the plan except any participants deemed to be grandfathered participants.

The postretirement healthcare plan, closed to new participants in 2010, provides a portion of health insurance benefits for retired and covered corporate and OTP employees. To be eligible for retiree health insurance benefits, the employee must be 55 years of age with a minimum of 10 years of service. The plan is an unfunded plan and accordingly holds no plan assets.

Pension Plan Assets. We have established an investment committee, comprised of members of management of the Company, to develop and monitor our investment strategy for our Pension Plan assets. Our investment strategy includes the following objectives:

•The assets of the plan will be invested in accordance with all applicable laws in a manner consistent with fiduciary standards including Employee Retirement Income Security Act standards of 1974 (ERISA) (if applicable). Specifically:

◦The safeguards and diversity that a prudent investor would adhere to must be present in the investment program.

◦All transactions undertaken on behalf of the Pension Plan must be in the best interest of plan participants and their beneficiaries.

•The primary objective is to provide a source of retirement income for its participants and beneficiaries.

•The near-term primary financial objective is to improve and protect the funded status of the plan.

•A secondary financial objective is to minimize pension funding and expense volatility where possible.

We have developed an asset allocation target, measured at investment market value, to provide guideline percentages of investment mix. This investment mix is intended to achieve the financial objectives of the plan. The permitted range is a guide and will at times not reflect the actual asset allocation due to market conditions, actions of our investment managers and required cash flows to and from the Pension Plan.

The following table presents our target asset allocation permitted range along with the actual asset allocation as of December 31, 2025 and 2024:

Return Enhancement investments are those that seek to provide equity-like, long-term capital appreciation. Examples include equity securities, including dynamic asset allocation funds, and higher yielding fixed income securities, such as high yield bonds and emerging market debt.

Risk Management investments seek to decrease downside risk or act as a hedge against plan liabilities. Examples are cash and fixed income instruments.

Alternative investments seek to either provide return enhancement through long-term appreciation or risk management through decreased downside risk. The defining characteristics of these asset types are uncorrelated sources of returns, less liquidity and private market access. Examples include investments in the SEI Energy Debt Collective Fund.

The following presents the fair value inputs classified within the fair value hierarchy used to measure Pension Plan assets at December 31, 2025 and 2024 and assets measured using the net asset value (NAV) practical expedient:

The investments held by the SEI Energy Debt Collective Fund on December 31, 2025 and 2024 consist mainly of below investment grade high yield bonds and loans of U.S. energy companies.

Funded Status. The following table provides a reconciliation of the changes in the fair value of plan assets and the actuarially computed benefit obligation for the years ended December 31, 2025 and 2024 and the funded status of the plans as of December 31, 2025 and 2024:

The accumulated benefit obligation of our Pension Plan was $289.5 million and $288.5 million as of December 31, 2025 and 2024. The accumulated benefit obligation of our ESSRP was $35.1 million and $35.3 million as of December 31, 2025 and 2024.

The following assumptions were used to determine benefit obligations as of December 31, 2025 and 2024:

The measurement of the plan asset or benefit obligation recognized for our Pension Plan, ESSRP and postretirement healthcare benefit plan included the following significant actuarial adjustments:

•For the Pension Plan, an increase in the discount rate in 2025 and 2024 reduced our obligation by $0.4 million and $4.7 million. Changes in plan participant census data decreased our benefit obligation by $3.1 million in 2025. Actual returns on Pension Plan assets in 2025 were $33.6 million, compared to an expected return of $24.8 million, impacting our net obligation by $8.8 million.

•For the ESSRP, a decrease in the discount rate in 2025 increased our obligation by $0.5 million, and an increase in the discount rate in 2024 reduced our obligation by $0.2 million.

•For the postretirement healthcare plan, a decrease in the discount rate in 2025 increased our benefit obligation by $0.4 million and an increase in our discount rate in 2024 reduced our obligation by $0.2 million. Revised estimates of healthcare cost trends, participant contribution assumptions, and other trend assumptions increased the benefit obligation by $4.5 million in 2025. Changes in plan participant census data increased our benefit obligation by $0.9 million in 2025.

Net Periodic Benefit Cost. A portion of service cost may be capitalized as a cost of self-constructed property, plant and equipment. When recognized in the consolidated statements of income, service cost is recognized within one of the components of operating expenses. Nonservice cost components of net periodic benefit cost may be deferred and recognized as a regulatory asset under the accounting guidance for regulated operations. When recognized in the consolidated statements of income, nonservice cost components are recognized as nonservice cost components of postretirement benefits.

The following table lists the components of net periodic benefit cost of our defined benefit pension plans and other postretirement benefits for the years ended December 31, 2025, 2024 and 2023:

The following table includes the impact of regulation on the recognition of periodic benefit cost arising from pension and other postretirement benefits for the years ended December 31, 2025, 2024 and 2023:

The following assumptions were used to determine net periodic benefit cost for the years ended December 31, 2025, 2024 and 2023:

We develop our estimated discount rate through the use of a hypothetical bond portfolio method. This method derives the discount rate from the average yield of a collection of high credit quality bonds which produce cash flows similar to our anticipated future benefit payments. We estimate the assumed long-term rate of return on plan assets based primarily on asset category studies using historical market return and volatility data with forward-looking estimates based on existing financial market conditions and forecasts of capital markets. Modest excess return expectations versus some market indices are incorporated into the return projections based on the actively managed structure of the investment programs and their records of achieving such returns historically.

The following table presents the amounts not yet recognized as components of net periodic benefit cost as of December 31, 2025 and 2024:

Cash Flows. We did not make any contributions to our Pension Plan in 2025, 2024 or 2023. As of December 31, 2025, we had no minimum funding requirements for our Pension Plan. Contributions to our ESSRP and postretirement healthcare plan are equal to the benefits paid to plan participants.

The following reflects anticipated benefit payments to be paid in each of the next five years and in the aggregate for the five-year period thereafter under our pension plans and postretirement healthcare plan:

401K Plan

We sponsor a 401K plan for the benefit of all corporate and subsidiary company employees. Contributions made to these plans totaled $9.7 million for 2025, $9.3 million for 2024 and $7.8 million for 2023.

12. Asset Retirement Obligations

We have recognized AROs related to our coal-fired generation plants, natural gas combustion turbines, solar facility and wind turbines. The cost of AROs includes items such as site restoration, closure or removal of ash pits and removal of certain structures, generators, asbestos and storage tanks. We have other legal obligations associated with the retirement of a variety of other long-lived tangible assets used in electric operations where the estimated settlement costs are individually and collectively immaterial. We haveno assets legally restricted for the settlement of any AROs. As of December 31, 2025 and 2024, $0.1 million and $0.1 million respectively, was included in other current liabilities and $43.9 million and $42.1 million, respectively, was included in other noncurrent liabilities in the consolidated balance sheets related to AROs.

A reconciliation of the carrying amounts of AROs for the years ended December 31, 2025 and 2024 is as follows:

13. Income Taxes

Income before income taxes for the years ended December 31, 2025, 2024 and 2023 consists entirely of domestic earnings.

The provision for income taxes charged to income for the years ended December 31, 2025, 2024 and 2023 consisted of the following:

The reconciliation of the statutory federal income tax rate to our effective tax rate for each of the years ended December 31, 2025, 2024 and 2023 is as follows:

In the above table, the impact of regulation consists of excess deferred income taxes arising from the federal tax rate reduction in the 2017 Tax Cuts and Jobs Act and the impact of allowance for equity funds used during construction at OTP.

Energy-related tax credits, which consist of PTCs and ITCs, North Dakota wind tax credits, which are included with state taxes in the above table, and excess deferred income taxes are returned to customers as a reduction of the rates they are charged and result in a reduction of operating revenues.

Income tax payments by jurisdiction, net of refunds, were composed of the following for the years ended December 31, 2025, 2024 and 2023:

Deferred tax assets and liabilities were composed of the following on December 31, 2025 and 2024:

As of December 31, 2025, we had net operating loss carryforwards for state tax purposes totaling $2.5 million which expire between 2029 and 2047, state tax credits totaling $15.9 million which expire between 2041 and 2043, and federal tax credits totaling $2.0 million which expire in 2047.

The following table summarizes the activity for unrecognized tax benefits for the years ended December 31, 2025, 2024 and 2023:

The Company and its subsidiaries file a consolidated U.S. federal income tax return and various state income tax returns. As of December 31, 2025, with limited exceptions, we are no longer subject to examinations by taxing authorities for tax years prior to 2022 for federal and North Dakota income taxes and prior to 2021 for Minnesota state income taxes.

One Big Beautiful Bill Act

On July 4, 2025, broad spending and tax law legislation referred to as the One Big Beautiful Bill Act (OBBBA) was enacted in the U.S. The aspects of the law that impact our financial position and may impact our future investment opportunities include certain changes to corporate income taxes and modifications to existing renewable energy credits.

The OBBBA includes changes to corporate income tax rules and regulations, including reinstating 100% bonus depreciation, immediate expensing of domestic research and development costs, and modifications to the business interest expense limitation.

The effects of changes in tax laws and regulations are required to be recognized in our consolidated financial statements in the period of enactment. Accordingly, in 2025, we recognized a reduction to our current year income tax payable in the amount of $7.0 million, with a corresponding increase to our deferred income tax liability, as a result of electing to deduct previously deferred research and development costs in the current year. We also anticipate electing bonus depreciation for eligible assets in our 2025 corporate income tax return, which resulted in a reduction of our current year income tax payable and an increase to our deferred income tax liability.

The OBBBA also alters the timing and eligibility of certain tax credits for renewable energy projects. Wind and solar projects that begin construction by July 4, 2026 are eligible for technology-neutral tax credits (production tax credits or investment tax credits). Projects that begin construction after July 4, 2026 must be in service by December 31, 2027 to qualify for technology-neutral tax credits. For projects that begin construction after December 31, 2025, new provisions restrict tax credit eligibility for those projects involving material assistance or effective control by a Foreign Entity of Concern, as defined in the legislation, which includes entities linked to China, Russia, Iran or North Korea.

14. Commitments and Contingencies

Commitments

Electric Utility Capacity and Energy Requirements. OTP has commitments for the purchase of capacity and energy requirements under contractual agreements, including wind power purchase agreements extending into 2048. Generally, the terms of OTP's wind power purchase agreements require OTP to purchase all of the electricity generated by a particular wind farm, but do not include fixed or minimum payments. The required payments are variable and the amounts due are determined based upon the amount of capacity available or electricity generated. Capacity and energy requirement costs under these agreements totaled $4.1 million, $6.0 million and $5.6 million for the years ended December 31, 2025, 2024 and 2023.

Coal Purchase Commitments. OTP is party to contracts providing for the purchase and delivery of its coal requirements. OTP’s current coal purchase agreement with CCMC for Coyote Station expires on December 31, 2040. All of Coyote Station’s coal requirements for the period covered must be purchased under this agreement. The agreement is structured so that the price of the coal covers all of CCMC's operating, financing and future mine reclamation costs. In the table below, we have estimated the future payments to be made under the terms of the agreement until its maturity. OTP has an agreement for the purchase of Big Stone Plant’s coal requirements through December 31, 2026. There is no fixed minimum purchase requirement, and no amounts for this agreement have been included in the table below; however, under this agreement all of Big Stone Plant’s coal requirements for the period covered must be purchased under this agreement. Coal purchase costs under thesetwo agreements totaled $50.5 million, $44.7 million and $43.7 million for the years ended December 31, 2025, 2024 and 2023.

Equipment Purchase Commitments. As of December 31, 2025, OTP had commitments with third parties for the procurement, construction, delivery and installation of certain electric grid equipment which extend into 2028 and totaled approximately $53.1 million.

Land Easement Payments. OTP has commitments to make payments for land easements not classified as leases. The contractual terms of these easements are generally 99 years or do not have a stated maturity date; however, per the terms of the agreements, our requirement to make payment ends once we cease use of the land. As such, in the table below, we have included payments under these easements through the estimated useful lives of the facilities associated with the easement. The commitments under these arrangements extend into 2055 and total approximately $56.4 million. Land easement costs under these agreements totaled $1.9 million, $1.8 million and $1.8 million for the years ended December 31, 2025, 2024 and 2023.

Other Commitments. As of December 31, 2025, we had commitments under contracts for maintenance, software subscriptions and other services extending into 2046 which totaled approximately $23.0 million.

Our future commitments as of December 31, 2025 were as follows:

Solar Development. On October 30, 2024, OTP entered into an agreement to acquire the assets of a solar facility currently under development. The assets to be acquired include real property rights and interests, interconnection agreements, state and local permits, and other development assets. Per the agreement, the purchase price is equal to $23.6 million, plus the reimbursement of certain interconnection costs and costs to purchase and store the main power transformer. On January 9, 2026, OTP completed this acquisition at a total cost of $35.7 million, including reimbursements and fees.

Contingencies

Self-Funding of Transmission Upgrades for Generator Interconnections. FERC has granted transmission owners within MISO and other regional transmission organizations (RTOs) the unilateral authority to determine the funding mechanism for interconnection transmission upgrades that are necessary to accommodate new generation facilities connecting to the electrical grid. Under existing FERC orders, transmission owners can unilaterally determine whether the generator pays the transmission owner in advance for the transmission upgrade or, alternatively, the transmission owner can elect to fund the upgrade and recover over time from the generator the cost of and a return on the upgrade investment (a self-funding). FERC’s orders granting transmission owners this unilateral funding authority have been judicially contested on the basis that transmission owners may be motivated to discriminate among generators in making funding determinations. In the most recent judicial proceedings, the petitioners argued to the U.S. Court of Appeals for the District of Columbia that FERC did not comply with a previous judicial order to fully develop a record regarding the risk of discrimination and the financial risk absorbed by transmission owners for generator-funded upgrades. In December 2022, the Court of Appeals ruled in favor of the petitioners remanding the matter to FERC, instructing the agency to adequately explain the basis of its orders. The Court of Appeals decision did not vacate transmission owners’ unilateral funding authority.

In June 2024, FERC issued an Order to Show Cause proceeding against four RTOs, including MISO. Within its order, FERC indicates that the transmission tariffs of the RTOs appear to be unjust, unreasonable, and unduly discriminatory or preferential because they allow transmission owners to unilaterally elect transmission owner self-funding, which may increase costs, impose barriers to transmission interconnection and result in undue discrimination among interconnection customers.

The order required each RTO to submit filings to either 1) show cause as to why the transmission tariff remains just and reasonable and not duly discriminatory or preferential, or 2) to explain what changes to the tariff it believes would remedy the identified concerns. FERC has received a number of responses to its Order to Show Cause. In September 2024, in separate filings, MISO and transmission owners within MISO, including OTP, filed responses outlining the reasons why the self-funding option remains just and reasonable and not unduly discriminatory or preferential. Other responses have been provided by other RTOs, individual transmission owners, developers of renewable generation facilities and other interested parties.

OTP, as a transmission owner in MISO, has exercised its authority and elected to self-fund transmission upgrades necessary to accommodate new system generation. Under such an election, OTP is recovering the cost of the transmission upgrade and a return on that investment from the generator over a contractual period of time. Should the resolution of this matter eliminate transmission owners’ unilateral funding authority on either a prospective or retrospective basis, our financial results would be impacted. We cannot at this time reasonably predict the outcome of this matter given the uncertainty as to how FERC may ultimately decide on the matter.

Class Action Lawsuits and Related Matters. Beginning in August of 2024, a series of putative federal class action lawsuits consolidated under the caption In re: PVC Pipe Antitrust Litigation (Case No. 1:24-cv-07639) were filed in the United States District Court for the Northern District of Illinois against Northern Pipe Products, Vinyltech Corporation, Otter Tail Corporation and more than twenty other PVC pipe manufacturers, as well as Oil Price Information Systems, LLC (OPIS), a reporting service that provides pricing and market intelligence in various industries, including the PVC pipe industry during the relevant period. The Court has allowed three putative classes to file complaints: a Direct Purchaser Class, a Non-Converter Seller Purchaser Class and an End-User Class.

In July 2025, the Court preliminarily approved a settlement agreement among the Direct Purchaser Class, the Non-Converter Seller Purchaser Class and OPIS. The settlement agreement resolved claims against OPIS and provides for its cooperation with the plaintiffs.

In August of 2025, thethree putative classes each filed a first or an amended complaint alleging, among other things, that beginning in January 2017 or January 2020, depending on the class, the defendants and alleged co-conspirators conspired to fix, raise, maintain and stabilize the price of PVC municipal pipe, PVC plumbing pipe, PVC electrical pipe and PVC pipe fittings in violation of U.S. federal and state antitrust laws. The complaints allege that PVC pipe manufacturers improperly exchanged confidential information through OPIS and engaged in other indirect and direct communications with each other. Plaintiffs are seeking treble damages, injunctive relief, pre- and post-judgment interest, costs and attorneys' fees on behalf of the putative classes.

On October 30, 2025, the defendants, including OTC, filed motions to dismiss. Briefings on these motions were completed in early 2026, and at this time no Court decision has been issued on the motions.

In August 2024, the Company received a grand jury subpoena issued by the U.S. District Court for the Northern District of California, from the U.S. Department of Justice (DOJ) Antitrust Division. The subpoena calls for production of documents regarding the manufacturing, selling and pricing of PVC pipe. The Company has responded to the subpoena and intends to comply with its obligations thereunder. On October 7, 2025, the DOJ filed a motion to intervene and for a partial stay of document discovery for a period of six months in In Re: PVC Pipe Antitrust Litigation, which the Court granted on October 10, 2025.

On September 26, 2025, a putative nation-wide class action complaint (Case No. S-257310) was filed in the Supreme Court of British Columbia, Canada against Northern Pipe, Vinyltech Corporation, Otter Tail Corporation and several other PVC pipe manufacturers, as well as OPIS. The complaint alleges that the defendants, beginning in 2021, conspired to fix, raise, maintain, and stabilize the price of PVC pipe through an information exchange, OPIS, breaching Canada's Competition Act, and creating tortious liability. The plaintiffs seek general damages, injunctive relief, pre- and post-judgment interest, punitive damages, cost, and attorneys' fees on behalf of the putative class.

The Company believes there are factual and legal defenses to the allegations in the complaints and is defending itself accordingly. There remains considerable uncertainty regarding the timing or ultimate resolution of these matters. At this time, we are unable to determine the likelihood of an outcome or estimate a range of reasonably possible losses, if any, arising from the class action complaints in the United States and Canada or the DOJ investigation. The resolution of these matters could have a material impact on the Company’s financial position, operating results and liquidity, and it is reasonably possible that our estimate of a loss arising from these matters could change in the near term.

On May 20, 2025, the Otter Tail Corporation Board of Directors received a letter from counsel submitted on behalf of a shareholder, demanding the Board investigate and take legal action against certain current and former directors and officers of the Company. The derivative demand letter includes alleged securities law violations and breach of fiduciary duties and unjust enrichment against certain current and former officers and directors of the company in connection with the matters at issue in the pending civil antitrust cases. At this time, we are unable to determine the likelihood of any outcome related to this matter.

Other Contingencies. We are involved in claims, legal proceedings, investigations and regulatory matters arising in the normal course of business. We regularly analyze relevant information and, as necessary, estimate and record accrued liabilities for legal, regulatory enforcement and other matters in which a loss or range of loss is probable of occurring and can be reasonably estimated. We believe the effect on our consolidated operating results, financial position and cash flows, if any, for the disposition of all matters pending as of December 31, 2025, other than those discussed above, will not be material.

15. Stockholders' Equity

Capital Structure

In addition to authorized and outstanding common stock, the Company has 1,500,000 authorized no par value cumulative preferred shares and 1,000,000 authorized no par value cumulative preference shares. No cumulative preferred or cumulative preference shares were outstanding at December 31, 2025 or 2024.

Registration Statements

On May 3, 2024, we filed a shelf registration statement with the SEC under which we may offer for sale, from time to time, either separately or together in any combination, equity, debt or other securities described in the shelf registration statement. The registration statement expires in May 2027. No shares were issued pursuant to the shelf registration statement in 2025.

On May 3, 2024, we filed a second registration statement with the SEC for the issuance of up to 1,500,000 common shares under an Automatic Dividend Reinvestment and Share Purchase Plan, which provides shareholders, retail customers of OTP and other interested investors methods of purchasing our common shares by reinvesting their dividends or making optional cash investments. Shares purchased under the plan may be new issue common shares or common shares purchased on the open market. In 2025, we issued 98,710 common shares under this program and no proceeds were received, as all shares issued were purchased on the open market. As of December 31, 2025,1,330,821 shares remained available for purchase or issuance under the plan. The registration statement expires in May 2027.

Dividend Restrictions

OTC is a holding company with no significant operations of its own. The primary source of funds for payments of dividends to our shareholders is from intercompany distributions made by OTC's subsidiaries to OTC.

As a result of potential restrictions under our financing agreements, certain statutory limitations or regulatory requirements, our ability to pay dividends, or our subsidiaries' ability to provide funding to OTC for the payment of dividends may be limited, as further described below:

Both the OTC Credit Agreement and OTP Credit Agreement contain restrictions on the payment of cash dividends upon a default or event of default, including failure to maintain certain financial covenants. As of December 31, 2025, we were in compliance with these financial covenants.

Under the Federal Power Act, a public utility may not pay dividends from any funds properly included in a capital account. What constitutes “funds properly included in a capital account” is undefined in the Federal Power Act and the related regulations;

however, the FERC has consistently interpreted the provision to allow dividends to be paid as long as i) the source of the dividends is clearly disclosed, ii) the dividend is not excessive and iii) there is no self-dealing on the part of corporate officials.

The MPUC indirectly limits the amount of dividends OTP can pay to OTC by requiring an equity-to-total-capitalization ratio between 46.7% and 57.1%, with total capitalization not to exceed $2.4 billion based on OTP’s capital structure requirements as of December 31, 2025. As of December 31, 2025, OTP’s equity-to-total-capitalization ratio including short-term debt was 53.8% and its net assets restricted from distribution totaled approximately $896.9 million.

16. Accumulated Other Comprehensive Income (Loss)

The Company's accumulated other comprehensive income (loss) consists of unamortized actuarial gains and losses and prior service costs related to pension and other postretirement benefits and unrealized gains and losses on marketable securities classified as available-for-sale. The income tax expense or benefit associated with amounts reclassified from accumulated other comprehensive income (loss) and reflected in the consolidated statements of income are recognized in the same period as the amounts are reclassified.

The following table shows the changes in accumulated other comprehensive income (loss) for the years ended December 31, 2025, 2024 and 2023:

17. Share-Based Payments

Employee Stock Purchase Plan

The 1999 Employee Stock Purchase Plan, as amended, authorizes the issuance of 1,400,000 common shares, allowing eligible employees to purchase our common shares through payroll withholding at a discount of up to 15% off the market price at the end of eachsix-month purchase period. Employee withholding amounts may not be less than $10 or more than $2,000 per month, subject to certain limitations, as described in the plan. A plan participant may cease making payroll deductions at any time. A participant may not purchase more than 2,000 shares in a givensix-month purchase period under the plan and may not purchase more than $25,000 (fair market value) of common shares under the plan and all other purchase plans (if any) in a calendar year. A participant may withdraw from the plan at any time and elect to receive the balance of their contributions to the plan that have not yet been used to purchase shares. Shares purchased under the plan are automatically enrolled in the Company's dividend reinvestment plan. Shares purchased under the plan may not be assigned, transferred, pledged, or otherwise disposed, except for certain situations allowed by the plan, such as upon death, for a period of 18 months after purchase. At our discretion, shares purchased under the plan can be either new issue shares or shares purchased in the open market. The plan shall automatically terminate when all of the shares authorized under the plan have been issued.

We recognize the 15% discount to the fair market value of the purchased shares as stock-based compensation expense, which amounted to $0.4 million, $0.4 million and $0.3 million for the years ended December 31, 2025, 2024 and 2023. For the years ended December 31, 2025, 2024 and 2023, the number of shares issued under the plan was 34,955,31,252 and 26,348 shares. As of December 31, 2025, there were 171,160 shares available for purchase under the plan.

Share-Based Compensation Plan

The 2023 Stock Incentive Plan, which was approved by our shareholders in April 2023, authorizes the issuance of 979,891 common shares for the granting of stock options, stock appreciation rights, restricted stock, restricted stock units, dividend equivalents, performance awards and other stock-based awards. In addition, common shares subject to any outstanding awards under our prior stock incentive plans that are forfeited, canceled or reacquired by the Company will become available for re-issuance under the 2023 Stock Incentive Plan. As of December 31, 2025,695,826 shares were available for issuance under the plan. The plan terminates on April 17, 2033.

We grant restricted stock awards to our employees and members of our Board of Directors and stock performance awards to our executive officers and certain other key employees as part of our long-term compensation and retention program. Stock-based compensation cost, recognized within operating expenses in the consolidated statements of income, amounted to $8.7 million, $9.1 million and $7.4 million for the years ended December 31, 2025, 2024 and 2023. The related income tax benefit recognized for these periods amounted to $2.0 million, $2.7 million and $1.6 million.

Restricted Stock Awards. Restricted stock awards are granted to executive officers and other key employees and members of the Company's Board of Directors. The awards vest, depending on award recipient, either ratably over a period ofthree tofour years or cliff vest after four years. Vesting is accelerated in certain circumstances, including upon retirement. Awards granted to members of the Board of Directors are issued and outstanding upon grant and carry the same voting and dividend rights of unrestricted outstanding common stock. Awards granted to executive officers are eligible to receive dividend equivalent payments during the vesting period, subject to forfeiture under the terms of the agreement, but such awards are not issued or outstanding upon grant and do not provide for voting rights.

The grant-date fair value of each restricted stock award is determined based on the market price of the Company's common stock on the date of grant adjusted to exclude the value of dividends for those awards that do not receive dividend or dividend equivalent payments during the vesting period.

The following is a summary of restricted stock award activity for the year ended December 31, 2025:

The weighted-average grant-date fair value of granted awards was $74.20, $85.25 and $68.03 during the years ended December 31, 2025, 2024 and 2023. The fair value of vested awards was $3.6 million, $5.1 million and $3.1 million during the years ended December 31, 2025, 2024 and 2023. As of December 31, 2025, there was $3.7 million of unrecognized compensation cost for unvested restricted stock awards to be recognized over a weighted-average period of 1.86 years.

Stock Performance Awards. Stock performance awards are granted to executive officers and certain other key employees. The awards vest at the end of athree-year performance period. The number of common shares awarded, if any, at the end of the performance period ranges from zero to 150% of the target amount based ontwo performance measures i) total shareholder return relative to a peer group (TSR component) and ii) return on equity (ROE component). The awards have no voting or dividend rights during the vesting period. Vesting of the awards is accelerated in certain circumstances, including upon retirement. The number of common shares awarded on an accelerated vesting is based on actual performance at the end of the performance period.

The grant-date fair value of the ROE component of the stock performance awards granted during the years ended December 31, 2025, 2024 and 2023 was determined using the grant-date stock price and a discounted cash flow analysis to adjust for expected unearned dividends during the vesting period. The grant-date fair value of the TSR component of the stock performance awards granted during the years ended December 31, 2025, 2024 and 2023 was determined using a Monte Carlo fair value simulation model incorporating the following assumptions:

The risk-free interest rate was derived from yields on U.S. government bonds of a similar term. The expected term of the award is equal to thethree-year performance period. Expected volatility was estimated based on actual historical volatility of our common stock over athree-year period. Dividend yield was estimated based on historic and future yield estimates.

The following is a summary of stock performance award activity for the year ended December 31, 2025 (share amounts reflect awards at target):

The weighted-average grant-date fair value of granted awards was $73.90, $94.45 and $61.97 during the years ended December 31, 2025, 2024 and 2023. The fair value of vested awards was $5.5 million, $12.3 million and $5.3 million during the years ended December 31, 2025, 2024 and 2023. As of December 31, 2025, there was $0.2 million of unrecognized compensation cost of unvested stock performance awards to be recognized over a weighted-average period of 0.96 years.

18. Earnings Per Share

The numerator used in the calculation of both basic and diluted earnings per share is net income. The denominator used in the calculation of basic earnings per share is the weighted-average number of shares outstanding during the period. The denominator used in the calculation of diluted earnings per share is derived by adjusting basic shares outstanding for the dilutive effect of potential shares outstanding, which consist of shares associated with time- and performance-based stock awards and our employee stock purchase plan.

The following includes the computation of the denominator for basic and diluted weighted-average shares outstanding for the years ended December 31, 2025, 2024 and 2023:

The number of shares excluded from diluted weighted-average common shares outstanding because such shares were anti-dilutive was not material for the years ended December 31, 2025, 2024 and 2023.

19. Derivative Instruments

OTP enters into derivative instruments to manage its exposure to future commodity price variability, specifically future wholesale energy and natural gas prices, and reduce volatility in prices for our retail electric customers. These derivative instruments are not designated as qualifying hedging transactions but provide for an economic hedge against future price variability. The instruments are recorded at fair value on the consolidated balance sheets on a gross basis with assets and liabilities presented separately. In accordance with rate-making and cost recovery processes, we recognize a regulatory asset or liability to defer losses or gains from derivative activity until settlement of the associated derivative instrument.

As of December 31, 2025 and 2024, OTP had multiple outstanding pay-fixed, receive-variable swap agreements. The contracts outstanding as of December 31, 2025 had various settlement dates throughout 2026. The following presents the notional amounts and fair value of our derivative instruments as of December 31, 2025 and 2024:

During the years ended December 31, 2025 and 2024, contracts matured and were settled in an aggregate amount of a $2.1 million loss and a $3.5 million loss, respectively. Gains and losses recognized on the settlement of derivative instruments are returned to, or recovered from, our electric customers through fuel recovery mechanisms in each state. When recognized in the consolidated statements of income, these gains or losses are included in electric purchased power. Gains or losses related to the settlement of derivative instruments are included in cash flows from operations in the consolidated statements of cash flows.

20. Fair Value Measurements

The following tables present our assets and liabilities measured at fair value on a recurring basis as of December 31, 2025 and 2024 classified by the input method used to measure fair value:

Level 1 fair value measurements are based on quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access at the measurement date.

The level 2 fair value measurements for government and corporate debt securities are determined based on valuations provided by third parties which utilize industry accepted valuation models and observable market inputs to determine valuation. Some valuations or model inputs used by the pricing services may be based on broker quotes.

The level 2 fair value measurements for derivative instruments are determined by using inputs such as forward electric commodity prices, adjusted for location differences. These inputs are observable in the marketplace throughout the full term of the instrument, can be derived from observable data or are supported by observable levels at which transactions are executed in the marketplace.

In addition to assets recorded at fair value on a recurring basis, we also hold financial instruments that are not recorded at fair value in the consolidated balance sheets but for which disclosure of the fair value of these financial instruments is provided. The following reflects the carrying value and estimated fair value of these assets and liabilities as of December 31, 2025 and 2024:

The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that fair value:

Cash Equivalents: The carrying amount approximates fair value because of the short-term maturity of these instruments. Fair value is determined based on quoted prices in active markets, a Level 1 fair value input.

Short-Term Debt: The carrying amount approximates fair value because the debt obligations are short-term in nature and balances outstanding are subject to variable rates of interest which reset frequently, a Level 2 fair value input.

Long-Term Debt: The fair value of long-term debt is estimated based on current market indications for borrowings of similar maturities with similar terms, a Level 2 fair value input.