ALLIANT ENERGY CORP

Rate Reviews

Retail Base Rate Filings -Base rate changes reflect both returns on additions to infrastructure and recovery of changes in costs incurred or expected to be incurred to provide electric and gas service to retail customers. Given that a portion of the rate changes will offset changes in costs, revenues from rate changes should not be expected to result in an equal change in net income for either IPL or WPL.

IPL’s Retail Electric and Gas Rate Reviews (October 2024 Through September 2025 Forward-looking Test Period) - In September 2024, the IUC issued an order for IPL’s retail electric and gas rate reviews for the October 2024 through September 2025 forward-looking Test Period with rate changes effective October 1, 2024. Key drivers for the rate review included revenue requirement impacts of increasing electric and gas rate base, including investments in solar generation, as well as updated depreciation rates and certain incremental costs incurred resulting from the 2020 derecho windstorm. The IUC’s order included the following provisions:

•Annual retail electric base rate increase of $185 million, with customers receiving partially offsetting credits for the first 12 months through a tax benefit rider totaling $52 million and $16 million in 2025 and 2024, respectively, and a subsequent retail electric base rate moratorium through September 2029;

•During the moratorium, IPL may request updated rates if its actual return on common equity is 100 or more basis points below the authorized return on common equity for a single calendar year or 50 or more basis points below the authorized return on common equity for two consecutive years, and/or if a material change in laws or regulations causes the moratorium to become unsustainable;

•Annual retail gas base rate increase of $10 million;

•Electric earnings sharing mechanism beginning in calendar year 2025, where IPL would apply excess earnings to the remaining net book value of IPL’s highest earning asset with advance ratemaking principles (currently the Emery Generation Station) based on its authorized return on common equity as follows;

•Investment tax credits resulting from renewable generation and energy storage projects may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any revenue deficiency in future years;

•Creation of an individual customer rate tariff, which would allow IPL to attract new load growth to its service territory;

•Electric distribution system investment cap not to exceed $900 million in aggregate or $325 million in any given year from 2026 through 2029, with certain exceptions;

•IPL to retain renewable production tax credits from new generation resources not included in base rates and the repowering of existing wind farms, including the Franklin County wind farm refurbishment, as well as retain energy margins for new generation resources and energy storage;

•Discontinuation of the renewable energy rider; and

•A return of the remaining net book value of the Lansing Generating Station; however, the IUC’s order does not include a return on the remaining net book value of Lansing, resulting in Alliant Energy and IPL recording a pre-tax non-cash charge of $60 million to “Asset valuation charge for IPL’s Lansing Generating Station” in their income statements in 2024.

IPL filed a subsequent proceeding with the IUC in December 2025 for its October 2024 through September 2025 forward-looking Test Period retail electric and gas rate reviews, which compared actual revenues and costs to those initially forecasted by IPL. IPL currently does not expect any rate adjustments from this subsequent proceeding.

WPL’s Retail Electric and Gas Rate Reviews (2026/2027 Forward-looking Test Period) - In December 2025, the PSCW issued an order authorizing annual base rate increases of $69 million and $7 million for WPL’s retail electric and gas customers, respectively, effective January 1, 2026, for the 2026 forward-looking Test Period. The PSCW’s order also authorized WPL to implement an additional $75 million and $5 million increase in annual rates for its retail electric and gas customers, respectively, effective January 1, 2027, for the 2027 forward-looking Test Period. The key drivers for the annual base rate increases include revenue requirement impacts of increasing electric and gas rate base, including wind refurbishment projects, energy storage, existing natural gas-fired EGU improvements, solar generation costs incurred that exceed the construction cost estimates previously approved by the PSCW (refer to Note 3 for further discussion), and electric and gas distribution investments. The order extends, with certain modifications, an earnings sharing mechanism through 2027. Under the earnings sharing mechanism, WPL will defer a portion of its earnings if its annual regulatory return on common equity exceeds 10.05% during the 2026/2027 Test Period. WPL must defer 50% of its excess earnings between 10.05% and 10.55%, and 100% of any excess earnings above 10.55%. The PSCW also authorized an AFUDC applied to 100% of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.

Rate Review Details - Details related to IPL’s and WPL’s key jurisdictions were as follows:

(a)Authorized returns on common equity may not be indicative of actual returns earned or projections of future returns.

(b)Average rate base amounts reflect IPL’s allocated retail share of rate base and do not include CWIP and were calculated using a forecasted 13-month average for the test period.

(c)Average rate base amounts include assets that do not have advance rate-making principles (9.65% return on common equity), production tax credits carryforwards for 1,000 MW of wind generating facilities placed in service in 2019 and 2020 (5% return on common equity), as well as the portion of Whispering Willow - East that does not earn a return on investment.

(d)Average rate base amounts reflect WPL’s allocated retail share of rate base and do not include CWIP or a cash working capital allowance, and were calculated using a forecasted 13-month average for the test period. The PSCW provides a return on selected CWIP and a cash working capital allowance by adjusting the percentage return on rate base.

LEGISLATIVE MATTERS

Tax Legislation

In August 2022, the Inflation Reduction Act of 2022 was enacted. The most significant provisions of the legislation for Alliant Energy, IPL and WPL relate to a 10-year extension of tax credits for clean energy projects, a new production tax credit for eligible solar projects, a standalone investment tax credit for energy storage projects, and the right to transfer renewable tax credits generated after 2022 to other corporate taxpayers. The legislation also established a requirement for corporations with income over $1 billion to pay a 15% minimum tax; however, Alliant Energy is currently below this income level. Alliant Energy, IPL and WPL are utilizing various provisions of the Inflation Reduction Act of 2022 to enhance the tax benefits expected from their current and planned renewable generation and energy storage projects, including transferring tax credits from such projects to other corporate taxpayers. Refer to Note 1(c) for discussion of the transfer of renewable tax credits to other corporate taxpayers.

In July 2025, the One Big Beautiful Bill Act was enacted, which modified various clean energy tax credits under the Inflation Reduction Act of 2022, including production tax credits and investment tax credits. The most significant provisions of the new legislation for Alliant Energy, IPL, and WPL relate to the accelerated phase out of clean energy tax credits for eligible wind and solar projects for which construction begins more than 12 months after the enactment date or for projects placed in service after 2027, and restricted access to clean energy tax credits for projects that begin construction after 2025 and receive impermissible amounts of construction support from entities with ties to certain foreign countries, including China. Additionally, in July 2025, the Presidential Administration directed the U.S. Department of the Treasury to strictly enforce the termination of clean energy tax credits, including issuing new and revised guidance in August 2025, to ensure that requirements concerning the beginning of construction are not circumvented.

Refer to “Customer Investments” for discussion of Alliant Energy’s, IPL’s and WPL’s current plans to develop and/or acquire new renewable generation and energy storage projects. Alliant Energy, IPL and WPL currently expect these planned renewable generation and energy storage projects would continue to be eligible for clean energy tax credits. If these renewable generation and energy storage projects do not begin construction within the anticipated timeframes or fail to meet other eligibility requirements, the amount of clean energy tax credits could be significantly reduced, which could adversely impact Alliant Energy’s, IPL’s and WPL’s financial condition and results of operations.

Refer to Note 11 for discussion of Iowa tax reform enacted in 2022.

Economic Development

In May 2024, the Major Economic Growth Attraction program was enacted in Iowa, which offers various tax incentives for up to two qualified businesses for certain large-scale projects with capital investments greater than $1 billion constructed on certified sites greater than 250 acres in Iowa. The most significant provision of this program for Alliant Energy encourages economic development in IPL’s service territory. Alliant Energy has various development-ready sites throughout Iowa, including the Prairie View Industrial Center Super Park in Ames, Iowa and the River City Industrial Center in Mason City, Iowa.

In July 2023, legislation was enacted in Wisconsin, which creates a sales and use tax exemption for the sale of certain property for qualified data centers. The most significant provision of this legislation for Alliant Energy encourages economic development in WPL’s service territory.

Advance Rate-making Principles

In May 2024, legislation was enacted in Iowa related to the advance rate-making principles for certain generation and energy storage investments located in Iowa. The most significant provisions of this legislation for Alliant Energy would allow IPL to include energy storage and nuclear-fired generation projects in the advance rate-making principles request process prior to making these investments in Iowa, and require IPL to obtain a GCU Certificate from the IUC in order to construct energy storage projects.

LIQUIDITY AND CAPITAL RESOURCES

Overview - Alliant Energy, IPL and WPL expect to maintain adequate liquidity to operate their businesses and implement their strategy as a result of operating cash flows generated by their utility business, and available capacity under a single revolving credit facility and IPL’s sales of accounts receivable program, supplemented by periodic issuances of long-term debt and Alliant Energy equity securities. As summarized below, Alliant Energy, IPL and WPL believe they have the ability to generate and obtain adequate amounts of cash to meet their requirements and plans for cash in the next 12 months and beyond.

Liquidity Position -At December 31, 2025, Alliant Energy had $556 million of cash and cash equivalents, $1,212 million ($550 million at the parent company, $262 million at IPL and $400 million at WPL) of available capacity under the single revolving credit facility and no available capacity at IPL under its sales of accounts receivable program.

Capital Structure -Alliant Energy, IPL and WPL plan to maintain debt-to-total capitalization ratios that are consistent with investment-grade credit ratings, as well as maintain capital structures consistent with the authorized levels approved by IPL’s and WPL’s regulators. The following table shows financial capital structures as of December 31, 2025, as well as an adjusted capitalization structure that Alliant Energy believes is consistent with how a majority of the rating agencies currently view its junior subordinated notes:

(a)The long-term debt component of Alliant Energy’s financial capital structure includes junior subordinated notes classified as “Long-term debt, net” on Alliant Energy’s balance sheet (refer to Note 8(b) for additional information). The adjusted presentation at December 31, 2025 attributes 50% of the junior subordinated notes to common equity and 50% to long-term debt, to align with the debt-to-capital ratio used by the majority of rating agencies. The non-GAAP adjusted presentation reflecting this treatment is useful and relevant to investors in understanding how management and the rating agencies evaluate Alliant Energy’s capital structure.

Alliant Energy, IPL and WPL intend to manage their capital structures and liquidity positions in such a way that facilitates their ability to raise funds reliably and at reasonable terms and conditions, while maintaining capital structures consistent with those approved by regulators. In addition to capital structures, other important factors used to determine the characteristics of future financings include financial coverage ratios, capital spending plans, regulatory orders and rate-making considerations, levels of debt and equity imputed by rating agencies, market conditions, the impact of tax initiatives and legislation, and any potential proceeds from asset sales. The PSCW factors certain imputed debt adjustments, including certain lease obligations, in establishing a regulatory capital structure as part of WPL’s retail rate reviews. The IUC does not make any explicit adjustments for imputed debt in establishing capital ratios used in determining customer rates, although such adjustments are considered by IPL in recommending an appropriate capital structure. Debt imputations by rating agencies include, among others, AROs, pension and OPEB obligations, the sales of accounts receivable program and certain lease obligations.

Credit and Capital Markets -Alliant Energy, IPL and WPL maintain a single revolving credit facility to provide backstop liquidity to their commercial paper programs, and ensure a committed source of liquidity in the event the commercial paper market becomes disrupted. In addition, IPL maintains a sales of accounts receivable program as an alternative financing source; however, if customer arrears were to exceed certain levels, IPL’s access to the program may be restricted.

Primary Sources and Uses of Cash - Alliant Energy’s most significant source of cash is from electric and gas sales to IPL’s and WPL’s customers. Cash from these sales reimburses IPL and WPL for prudently-incurred expenses to provide service to their utility customers and generally provides IPL and WPL a return of and a return on the assets used to provide such services. Capital needed to retire debt and fund capital expenditures related to large strategic projects is expected to be met primarily through external financings.

Cash Flows - Selected information from the cash flows statements was as follows (in millions):

Operating Activities -The following items contributed to increased (decreased) operating activity cash flows for 2025 compared to 2024 (in millions):

(a)Refer to the cash flows statements for details of renewable tax credits transferred to other corporate taxpayers in 2024 and 2025.

Income Tax Payments and Receipts - Income tax (payments) receipts were as follows (in millions):

Alliant Energy, IPL and WPL currently do not expect to make any significant federal income tax payments over the next few years based on their current credit carryforward positions; however, some tax payments and receipts may occur for state taxes and between consolidated group members (including IPL and WPL) under the tax sharing agreement between Alliant Energy and its subsidiaries. Refer to Note 11 for discussion of the carryforward positions.

As discussed in “Legislative Matters,” the Inflation Reduction Act of 2022 provides the right to transfer renewable tax credits to other corporate taxpayers. Refer to the cash flows statements and Note 1(c) for details of renewable tax credits transferred to other corporate taxpayers. Alliant Energy, IPL and WPL currently intend to transfer all eligible renewable tax credits in the future.

Pension Plan Contributions - Alliant Energy, IPL and WPL currently expect to make $23 million, $3 million and $13 million of pension plan contributions in 2026, respectively, based on the funded status and assumed return on assets for each plan as of the December 31, 2025 measurement date. Refer to Note 12(a) for discussion of pension plan contributions in 2025 and the current funded levels of pension plans.

Investing Activities -The following items contributed to increased (decreased) investing activity cash flows for 2025 compared to 2024 (in millions):

(a)Largely due to higher expenditures for IPL’s energy storage and gas generation and IPL’s and WPL’s refurbishment of existing wind farms, partially offset by lower expenditures for IPL’s and WPL’s solar generation and WPL’s energy storage.