Form 8-K

8-K — ALLIANT ENERGY CORP

Accession: 0000352541-26-000030

Filed: 2026-05-01

Period: 2026-04-30

CIK: 0000352541

SIC: 4931 (ELECTRIC & OTHER SERVICES COMBINED)

Item: Results of Operations and Financial Condition

Item: Financial Statements and Exhibits

Documents

8-K — lnt-20260430.htm (Primary)

EX-99.1 (lnt043020268-kex991.htm)

GRAPHIC (alliantenergylogo.jpg)

XML — IDEA: XBRL DOCUMENT (R1.htm)

8-K

8-K (Primary)

Filename: lnt-20260430.htm · Sequence: 1

lnt-20260430

000035254100000524850000107832false00003525412026-04-302026-04-300000352541lnt:IplMember2026-04-302026-04-300000352541lnt:WplMember2026-04-302026-04-30

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d) of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) April 30, 2026

Name of Registrant, State of Incorporation, Address of Principal Executive Offices, Telephone Number, Commission File Number, IRS Employer Identification Number

ALLIANT ENERGY CORPORATION

(a Wisconsin corporation)

4902 N. Biltmore Lane

Madison, Wisconsin 53718

Telephone (608) 458-3311

Commission File Number - 1-9894

IRS Employer Identification Number - 39-1380265

INTERSTATE POWER & LIGHT COMPANY

(an Iowa corporation)

Alliant Energy Tower

Cedar Rapids, Iowa 52401

Telephone (319) 786-4411

Commission File Number - 1-4117

IRS Employer Identification Number - 42-0331370

WISCONSIN POWER & LIGHT COMPANY

(a Wisconsin corporation)

4902 N. Biltmore Lane

Madison, Wisconsin 53718

Telephone (608) 458-3311

Commission File Number - 0-337

IRS Employer Identification Number - 39-0714890

(Former name or former address, if changed since last report.)

This combined Form 8-K is separately filed by Alliant Energy Corporation, Interstate Power and Light Company and Wisconsin Power and Light Company.

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Alliant Energy Corporation, Common Stock, $0.01 Par Value, Trading Symbol LNT, Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Alliant Energy Corporation - Emerging growth company ☐

Interstate Power and Light Company - Emerging growth company ☐

Wisconsin Power and Light Company - Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.

Alliant Energy Corporation ☐

Interstate Power and Light Company ☐

Wisconsin Power and Light Company ☐

Item 2.02 Results of Operations and Financial Condition.

On April 30, 2026, Alliant Energy Corporation issued a press release announcing its financial results for the three months ended March 31, 2026. A copy of such press release is furnished as Exhibit 99.1 and is incorporated by reference herein.

Item 9.01 Financial Statements and Exhibits.

(a)Not applicable.

(b)Not applicable.

(c)Not applicable.

(d)Exhibits. The following exhibits are being furnished herewith:

Exhibit Number Description

(99.1)

Alliant Energy Corporation press release dated April 30, 2026

(104) Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrants have duly caused this report to be signed on their behalf by the undersigned hereunto duly authorized.

ALLIANT ENERGY CORPORATION

Date: April 30, 2026

By: /s/ Dylan M. Syse

Dylan M. Syse

Chief Accounting Officer and Controller

INTERSTATE POWER AND LIGHT COMPANY

Date: April 30, 2026

By: /s/ Dylan M. Syse

Dylan M. Syse

Chief Accounting Officer and Controller

WISCONSIN POWER AND LIGHT COMPANY

Date: April 30, 2026

By: /s/ Dylan M. Syse

Dylan M. Syse

Chief Accounting Officer and Controller

EX-99.1

Filename: lnt043020268-kex991.htm · Sequence: 2

Document

Exhibit 99.1

Alliant Energy Corporation

Corporate Headquarters

4902 North Biltmore Lane

Madison, WI 53718-2148

www.alliantenergy.com

News Release

FOR IMMEDIATE RELEASE

ALLIANT ENERGY ANNOUNCES FIRST QUARTER 2026 RESULTS

•First quarter GAAP earnings per share were $0.87 in 2026, compared to $0.83 in 2025

•First quarter ongoing earnings per share were $0.82 in 2026, compared to $0.83 in 2025

•Reaffirming 2026 ongoing earnings guidance range of $3.36 - $3.46 per share

•Signed an approximately 370 MW electric service agreement in Iowa, total contracted data center demand is now approximately 3.4 GW

MADISON, Wis. - April 30, 2026 - Alliant Energy Corporation (NASDAQ: LNT) today announced U.S. generally accepted accounting principles (GAAP) consolidated unaudited earnings per share (EPS) of $0.87 for first quarter 2026, compared to $0.83 for the first quarter of 2025. Ongoing EPS for first quarter 2026 was $0.82, compared to $0.83 for the first quarter of 2025.

Alliant Energy reaffirmed its consolidated ongoing EPS guidance for 2026 of $3.36 - $3.46, continuing its over a decade strong track record of compound annual earnings growth of more than 6%.

“We are off to a strong start in 2026, delivering approximately 25% of our ongoing earnings guidance midpoint, and reaffirming our full-year ongoing EPS outlook,” said Lisa Barton, Alliant Energy President and CEO. “Our results reflect disciplined execution and continued momentum in data center growth, including the signing of a new electric service agreement in Iowa for approximately 370 megawatts of contracted demand. With five executed agreements, we are translating customer demand into well-structured, long-term growth that benefits investors, existing customers and communities.”

Alliant Energy Consolidated EPS: GAAP EPS Non-GAAP EPS

2026 2025 2026 2025

Three months ended March 31 $0.87 $0.83 $0.82 $0.83

In 2026, the primary drivers of Alliant Energy’s results were higher revenue requirements from increasing rate base at IPL and WPL of $0.05 and $0.10 per share, respectively, including investments in generation and energy storage, non-GAAP adjustments in 2026, and higher allowance for funds used during construction. These items were offset by higher financing and depreciation expense related to capital investments, as well as other operating and maintenance expense primarily due to increased electric distribution and generation costs from planned maintenance activities and the addition of new energy resources.

Retail electric and gas sales decreased an estimated $0.04 and $0.03 per share in 2026 and 2025, respectively, due to impacts of temperatures on customer demand.

Alliant Energy’s Non-GAAP, or ongoing, EPS for 2026 excludes $0.05 per share benefit related to the remeasurement of deferred tax assets, reflecting a remeasurement of estimated state income tax apportionment. In the third quarter of 2025, WPL entered into an electric service agreement with a customer who expected to build a data center in WPL’s service territory. In the first quarter of 2026, the customer selected an alternative data center location in IPL’s service territory, and as a result, the electric service agreement with WPL was terminated and subsequently renegotiated and executed with IPL. This non-GAAP adjustment is presented to supplement GAAP results and highlight financial measures not typically associated with ongoing operations.

2026 Earnings Guidance

Alliant Energy is reaffirming its consolidated ongoing EPS guidance for 2026 of $3.36 - $3.46 per diluted share. Assumptions for Alliant Energy’s 2026 EPS guidance include, but are not limited to:

•Ability of IPL and WPL to earn their authorized rates of return

•Normal temperatures in its utility service territories

•Stable economy and resulting implications on utility sales

•Execution of capital expenditure plans, including achievement of targeted in-service dates

•Execution of cost controls and financing plans

•Consolidated effective tax rate of (29%)

The 2026 earnings guidance does not include the impacts of any material non-cash valuation adjustments, regulatory-related charges or credits, reorganizations or restructurings, future changes in laws, regulations or regulatory policies, adjustments made to deferred tax assets and liabilities from changes in forecasted state income tax apportionment and valuation allowances including further corporate tax rate changes in Iowa, changes in credit loss liabilities related to guarantees, pending lawsuits and disputes, settlement charges related to pension and other postretirement benefits plans, federal and state income tax audits and other Internal Revenue Service proceedings, impacts from changes to the authorized return on equity for ATC LLC, or changes in GAAP and tax methods of accounting that may impact the reported results of Alliant Energy.

Earnings Conference Call

A conference call to review the 2026 results is scheduled for Friday, May 1, 2026 at 9 a.m. central time. Alliant Energy President and Chief Executive Officer Lisa Barton, and Executive Vice President and Chief Financial Officer Robert Durian will host the call. The conference call is open to the public and can be accessed in two ways. Interested parties may listen to the call by dialing 800-715-9871 (Toll-Free) or 646-307-1963 (International), conference ID 9124041. Interested parties may also listen to a webcast at www.alliantenergy.com/investors. In conjunction with the information in this earnings announcement and the conference call, Alliant Energy posted supplemental materials on its website. An archive of the webcast will be available on the Company’s website at www.alliantenergy.com/investors for 12 months.

About Alliant Energy Corporation

Alliant Energy is the parent company of two public utility companies - Interstate Power and Light Company and Wisconsin Power and Light Company - and of Alliant Energy Finance, LLC, the parent company of Alliant Energy’s non-utility operations. Alliant Energy, whose core purpose is to serve customers and build stronger communities, is an energy-services provider with utility subsidiaries serving approximately 1,010,000 electric and 435,000 natural gas customers. Providing its customers in the Midwest with regulated electricity and natural gas service is the Company’s primary focus. Alliant Energy, headquartered in Madison, Wisconsin, is a component of the S&P 500 and is traded on the Nasdaq Global Select Market under the symbol LNT. For more information, visit the Company’s website at www.alliantenergy.com.

Contacts

Investors

Susan Gille

(608) 458-3956

investorrelations@alliantenergy.com

Media Hotline

(608) 458-4040

Forward-Looking Statements

This press release includes forward-looking statements. These forward-looking statements can be identified by words such as “forecast,” “expect,” “guidance,” or other words of similar import. Similarly, statements that describe future financial performance or plans or strategies are forward-looking statements. Such forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those expressed in, or implied by, such statements. Actual results could be materially affected by the following factors, among others:

•IPL’s and WPL’s ability to obtain adequate and timely rate relief to allow for, among other things, recovery of and/or the return on costs, including fuel costs, operating costs, transmission costs, capacity costs, costs of cancelled generation projects incurred prior to pursuing regulatory approval, as well as costs of generation projects incurred prior to regulatory approval or that exceed initial estimates, deferred expenditures, deferred tax assets, tax expense, interest expense, capital expenditures, marginal costs to service new customers, and remaining costs related to electric generating units (EGUs) that have been or may be permanently closed and certain other retired assets, environmental remediation costs, and decreases in sales volumes, as well as earning their authorized rates of return, payments to their parent of expected levels of dividends, the impact of rate design on current and potential customers and demand for energy in their service territories, and the ability to obtain regulatory approval with acceptable conditions for individual customer rates for large load growth customers;

•the impact of IPL’s retail electric base rate moratorium;

•the ability to obtain regulatory approval for construction projects with acceptable conditions;

•the ability to complete construction of generation and energy storage projects by planned in-service dates, with the expected earnings contributions and within the cost targets set by regulators due to cost increases of and access to materials, equipment and commodities, which could result from tariffs, including previously exempted tariffs related to solar project materials and equipment from certain countries, duties or other assessments, including antidumping or countervailing duties, inflation, labor issues or supply shortages, supply chain disruptions which may result from geopolitical issues, contractor performance, the ability to successfully resolve warranty issues or contract disputes, the ability to obtain adequate generator interconnection agreements to connect the new projects to Midcontinent Independent System Operator, Inc. (MISO) in a timely manner, the ability to obtain siting and environmental permits from local and state agencies and the ability of ITC Midwest LLC (ITC) and American Transmission Company LLC (ATC) to complete transmission upgrades in a timely manner;

•weather effects on utility sales volumes and operations;

•the direct or indirect effects resulting from cybersecurity incidents or attacks on Alliant Energy, IPL, WPL, or their suppliers, contractors and partners, or responses to such incidents;

•the impact of customer- and third party-owned generation and other non-traditional service models, including alternative electric suppliers and potential policy changes, regulatory changes, or legislation that may enable large customers to source behind-the-meter generation directly from third parties or to own or otherwise procure on-site or behind-the-meter generation or participate in co-located resource arrangements, in IPL’s and WPL’s service territories on system reliability, operating expenses and customers’ demand for electricity;

•economic conditions in IPL’s and WPL’s service territories, including the potential impacts of business or facility closures and tariffs;

•the ability and cost to attract large load growth customers and to provide sufficient generation and the ability of ITC and ATC to provide sufficient transmission capacity for potential load growth timely, including significant new commercial or industrial customers, such as data centers;

•the ability of potential large load growth customers to timely construct new facilities, due to local or state regulatory actions, zoning, siting, or permitting actions, public or community opposition or other factors, as well as the resulting higher system load demand by expected levels and timeframes;

•the impact of large load growth customers altering, delaying or cancelling planned facilities, including any resulting impacts of overbuilt or under-utilized transmission capacity or generation and energy storage assets;

•the impact of energy efficiency, franchise retention and customer disconnects on sales volumes and operating income;

•the impact that price changes may have on IPL’s and WPL’s customers’ demand for electric and gas services and their ability to pay their bills;

•changes in the price of delivered natural gas, transmission, purchased electric energy, purchased electric capacity and delivered coal, particularly during elevated market prices, and any resulting changes to counterparty credit risk, due to shifts in supply and demand caused by market conditions, regulations and MISO’s seasonal resource adequacy process;

•the ability to achieve the expected level of tax benefits for renewable generation and energy storage projects based on tax guidelines, timely beginning of construction and in-service dates, sourcing permissible amounts of construction and/or financing support from entities with ties to certain foreign countries, compliance with prevailing wage and apprenticeship requirements, project costs and the level of electricity output generated by qualifying generating facilities, and the ability to efficiently utilize the renewable generation and energy storage project tax benefits to achieve IPL’s authorized rate of return and for the benefit of IPL’s and WPL’s customers;

•federal and state regulatory or governmental actions, including the impact of legislation, Treasury regulations, executive orders, interpretations and guidance, and changes in public policy, including changes impacting renewable tax credits, including any repeal, modification, or reduced funding of the Inflation Reduction Act and the One Big Beautiful Bill Act, and siting generation and energy storage projects;

•the ability to utilize tax credits generated to date, and those that may be generated in the future, before they expire, as well as the ability to transfer tax credits that may be generated in the future at adequate pricing;

•the impacts of changes in the tax code, including tax rates, minimum tax rates, adjustments made to deferred tax assets and liabilities, changes in state income tax apportionment, and changes impacting the availability of and ability to transfer renewable tax credits, including preserving the qualification of any future tax credits;

•disruptions to ongoing operations and the supply of materials, services, equipment and commodities needed to continue to operate and maintain existing assets and to construct capital projects, which may result from geopolitical issues, tariffs, supplier manufacturing constraints, regulatory requirements, labor issues or transportation issues, and thus affect the ability to meet capacity requirements and result in increased capacity expense;

•inflation and higher interest rates;

•continued access to the capital markets on competitive terms and rates, and risks associated with potential increases in borrowing costs or reduced access to funding, and the actions of credit rating agencies;

•the future development of technologies related to electrification, and the ability to reliably store and manage electricity;

•employee workforce factors, including the ability to hire and retain employees with specialized skills, impacts from employee retirements, changes in key executives, ability to create desired corporate culture, collective bargaining agreements and negotiations, work stoppages or restructurings;

•disruptions in the supply and delivery of natural gas, purchased electricity and coal;

•changes to the creditworthiness of, or performance of obligations by, counterparties with which Alliant Energy, IPL and WPL have contractual arrangements, including large load growth customers, participants in the energy markets and fuel suppliers and transporters;

•the impact of penalties or third-party claims related to, or in connection with, a failure to maintain the security of personally identifiable information, including associated costs to notify affected persons and to mitigate their information security concerns;

•impacts that terrorist attacks may have on Alliant Energy’s, IPL’s and WPL’s operations and recovery of costs associated with restoration activities, or on the operations of Alliant Energy’s investments;

•changes to MISO’s interconnection or resource adequacy process establishing capacity planning reserve margin and capacity accreditation requirements that may impact how and when new and existing generating and energy storage facilities may be

accredited with energy capacity, and may require IPL and WPL to adjust their current resource plans, to add resources to meet the requirements of MISO’s process or to procure capacity in the market whereby such costs might not be recovered in rates;

•any legislative or regulatory changes that impose mandatory integrated resource planning requirements or materially modify existing planning processes, potentially affecting resource selection, cost recovery, and the ability to meet large load growth demand for energy;

•any material post-closing payments related to any past asset divestitures, including the transfer of renewable tax credits, which could result from, among other things, indemnification agreements, warranties, guarantees or litigation;

•issues associated with environmental remediation and environmental compliance, including compliance with all current environmental and emissions laws, regulations, siting requirements, and permits and future changes in environmental laws and regulations, including the Coal Combustion Residuals Rule, Cross-State Air Pollution Rule and federal, state or local regulations for emissions reductions, including greenhouse gases, from new and existing fossil-fueled EGUs under the Clean Air Act, and litigation associated with environmental requirements;

•increased pressure from customers, investors and other stakeholders to more rapidly reduce greenhouse gases emissions;

•the timely development of technologies, innovations and advancements to provide cost effective alternatives to traditional energy sources;

•the ability to defend against environmental claims brought by state and federal agencies, such as the U.S. Environmental Protection Agency and state natural resources agencies, or third parties, such as the Sierra Club, and the impact on operating expenses of defending and resolving such claims;

•the direct or indirect effects resulting from breakdown or failure of equipment in the operation of electric and gas distribution systems, such as mechanical problems, disruptions in telecommunications, technological problems, and explosions or fires, and compliance with electric and gas transmission and distribution safety regulations, including regulations promulgated by the Pipeline and Hazardous Materials Safety Administration;

•issues related to the availability and operations of EGUs and energy storage facilities, including start-up risks, breakdown or failure of equipment, fires, availability of warranty coverage and successful resolution of warranty issues or contract disputes for equipment breakdowns or failures, performance below expected or contracted levels of output or efficiency, operator error, employee safety, transmission constraints, compliance with mandatory reliability standards and risks related to recovery of resulting incremental operating, capacity, fuel-related and capital costs through rates;

•impacts that excessive heat, excessive cold, storms, wildfires, or natural disasters may have on Alliant Energy’s, IPL’s and WPL’s operations and construction activities, and recovery of costs associated with restoration activities, or on the operations of Alliant Energy’s investments;

•Alliant Energy’s ability to sustain its dividend payout ratio goal;

•changes to costs of providing benefits and related funding requirements of pension and other postretirement benefits plans due to the market value of the assets that fund the plans, economic conditions, financial market performance, interest rates, timing and form of benefits payments, life expectancies and demographics;

•material changes in employee-related benefit and compensation costs, including settlement losses related to pension plans;

•risks associated with operation and ownership of non-utility holdings, including potential impairments;

•changes in technology that alter the channels through which customers buy or utilize Alliant Energy’s, IPL’s or WPL’s products and services;

•risks associated with third-party risk management practices, including vendor financial condition, operational performance, cybersecurity incidents, and compliance with contractual and regulatory requirements;

•risks associated with large-scale internal technology modernization initiatives, including enterprise asset management systems, operational technology/informational technology integration, cloud transformation, and digital modernization, and the potential for delays, cost overruns, or operational impacts;

•impacts on equity income from unconsolidated investments from changes in valuations of the assets held, as well as potential changes to ATC’s authorized return on equity;

•impacts of IPL’s future tax benefits from Iowa rate-making practices, including deductions for repairs expenditures and cost of removal obligations, allocation of mixed service costs and state depreciation, and recoverability of the associated regulatory assets from customers, when the differences reverse in future periods;

•current or future litigation, regulatory investigations, proceedings or inquiries;

•reputational damage from negative publicity, protests, fines, penalties and other negative consequences resulting in regulatory and/or legal actions;

•the direct or indirect effects resulting from pandemics;

•the effect of accounting standards issued periodically by standard-setting bodies;

•the ability to successfully complete tax audits and changes in tax accounting methods with no material impact on earnings and cash flows; and

•other factors listed in the “2026 Earnings Guidance” section of this press release.

For more information about potential factors that could affect Alliant Energy’s business and financial results, refer to Alliant Energy’s most recent Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC), including the section therein titled “Risk Factors,” and its other filings with the SEC.

Without limitation, the expectations with respect to 2026 earnings guidance in this press release are forward-looking statements and are based in part on certain assumptions made by Alliant Energy, some of which are referred to in the forward-looking statements. Alliant Energy cannot provide any assurance that the assumptions referred to in the forward-looking statements or otherwise are accurate or will prove to be correct. Any assumptions that are inaccurate or do not prove to be correct could have a material adverse effect on Alliant Energy’s ability to achieve the estimates or other targets included in the forward-looking statements. The forward-looking statements included herein are made as of the date hereof and, except as required by law, Alliant Energy undertakes no obligation to update publicly such statements to reflect subsequent events or circumstances.

Use of Non-GAAP Financial Measures

To provide investors with additional information regarding Alliant Energy’s financial results, this press release includes reference to certain non-GAAP financial measures. These measures include income and EPS for the three months ended March 31, 2026 excluding the state income tax apportionment benefit at the Parent. Alliant Energy believes these non-GAAP financial measures are useful to investors because they provide an alternate measure to better understand and compare across periods the operating performance of Alliant Energy without the distortion of items that management believes are not normally associated with ongoing operations, and also provides additional information about Alliant Energy’s operations on a basis consistent with the measures that management uses to manage its operations and evaluate its performance. Alliant Energy’s management also uses income, as adjusted, to determine performance-based compensation.

In addition, Alliant Energy included in this press release IPL; WPL; Corporate Services; Utilities and Corporate Services; ATC Holdings; and Non-utility and Parent EPS for the three months ended March 31, 2026 and 2025. Alliant Energy believes these non-GAAP financial measures are useful to investors because they facilitate an understanding of segment performance and trends, and provide additional information about Alliant Energy’s operations on a basis consistent with the measures that management uses to manage its operations and evaluate its performance.

Reconciliation of the non-GAAP financial measures included in this press release to the most directly comparable GAAP financial measures are included in the earnings summaries that follow.

Note: Unless otherwise noted, all “per share” references in this release refer to earnings per diluted share.

ALLIANT ENERGY CORPORATION

EARNINGS SUMMARY (Unaudited)

The following tables provide a summary of Alliant Energy’s results for the three months ended March 31:

EPS: GAAP EPS Adjustments Non-GAAP EPS

2026 2025 2026 2025 2026 2025

IPL $0.36 $0.43 $— $— $0.36 $0.43

WPL 0.45 0.43 — — 0.45 0.43

Corporate Services 0.02 0.01 — — 0.02 0.01

Subtotal for Utilities and Corporate Services 0.83 0.87 — — 0.83 0.87

ATC Holdings 0.04 0.04 — — 0.04 0.04

Non-utility and Parent — (0.08) (0.05) — (0.05) (0.08)

Alliant Energy Consolidated $0.87 $0.83 ($0.05) $— $0.82 $0.83

Earnings (in millions): GAAP Income (Loss) Adjustments Non-GAAP Income (Loss)

2026 2025 2026 2025 2026 2025

IPL $94 $110 $— $— $94 $110

WPL 117 110 — — 117 110

Corporate Services 4 5 — — 4 5

Subtotal for Utilities and Corporate Services 215 225 — — 215 225

ATC Holdings 11 10 — — 11 10

Non-utility and Parent (2) (22) (12) — (14) (22)

Alliant Energy Consolidated $224 $213 ($12) $— $212 $213

Adjusted, or non-GAAP, earnings for the three months ended March 31 do not include the following item that was included in the reported GAAP earnings:

Non-GAAP Income Non-GAAP

Adjustments (in millions) EPS Adjustments

2026 2025 2026 2025

Non-utility and Parent:

State income tax apportionment benefit ($12) $— ($0.05) $—

Total Alliant Energy Consolidated ($12) $— ($0.05) $—

ALLIANT ENERGY CORPORATION

CONDENSED CONSOLIDATED STATEMENTS OF INCOME (Unaudited)

Three Months Ended March 31,

2026 2025

(in millions, except per share amounts)

Revenues:

Electric utility $888 $853

Gas utility 271 240

Other utility 2 13

Non-utility 23 22

Total revenues 1,184 1,128

Operating expenses:

Electric production fuel and purchased power 168 175

Electric transmission service 159 158

Cost of gas sold 173 137

Other operation and maintenance:

Energy efficiency costs 18 10

Non-utility Travero 16 16

Other 146 134

Depreciation and amortization 223 211

Taxes other than income taxes 32 30

Total operating expenses 935 871

Operating income 249 257

Other (income) and deductions:

Interest expense 142 119

Equity income from unconsolidated investments, net (22) (13)

Allowance for funds used during construction (30) (18)

Other (4) 3

Total other (income) and deductions 86 91

Income before income taxes 163 166

Income tax benefit (61) (47)

Net income attributable to Alliant Energy common shareowners $224 $213

Weighted average number of common shares outstanding:

Basic 257.4 256.8

Diluted 258.8 257.2

Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) $0.87 $0.83

ALLIANT ENERGY CORPORATION

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited)

March 31,

2026 December 31,

2025

(in millions)

ASSETS:

Current assets:

Cash and cash equivalents $115 $556

Other current assets 1,109 1,141

Property, plant and equipment, net 20,589 20,344

Investments 724 694

Other assets 2,276 2,256

Total assets $24,813 $24,991

LIABILITIES AND EQUITY:

Current liabilities:

Current maturities of long-term debt $— $1,074

Commercial paper 433 88

Other short-term borrowings 400 —

Other current liabilities 945 961

Long-term debt, net (excluding current portion) 11,007 10,954

Other liabilities 4,606 4,580

Alliant Energy Corporation common equity 7,422 7,334

Total liabilities and equity $24,813 $24,991

ALLIANT ENERGY CORPORATION

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)

Three Months Ended March 31,

2026 2025

(in millions)

Cash flows from operating activities:

Cash flows from operating activities excluding accounts receivable sold to a third party $475 $365

Accounts receivable sold to a third party (107) (116)

Net cash flows from operating activities 368 249

Cash flows used for investing activities:

Construction and acquisition expenditures:

Utility business (342) (554)

Other (72) (28)

Cash receipts on sold receivables 25 192

Other (4) (14)

Net cash flows used for investing activities (393) (404)

Cash flows from (used for) financing activities:

Common stock dividends (137) (130)

Proceeds from issuance of other short-term borrowings 400 —

Payments to retire long-term debt (1,075) —

Net change in commercial paper 395 220

Other 1 9

Net cash flows from (used for) financing activities (416) 99

Net decrease in cash, cash equivalents and restricted cash (441) (56)

Cash, cash equivalents and restricted cash at beginning of period 556 81

Cash, cash equivalents and restricted cash at end of period $115 $25

KEY FINANCIAL AND OPERATING STATISTICS

March 31, 2026 March 31, 2025

Common shares outstanding (000s) 258,277 256,876

Book value per share $28.74 $27.61

Quarterly common dividend rate per share $0.535 $0.5075

Three Months Ended March 31,

2026 2025

Utility electric sales (000s of megawatt-hours)

Residential 1,835 1,871

Commercial 1,602 1,599

Industrial 2,542 2,519

Industrial - co-generation customers 158 185

Retail subtotal 6,137 6,174

Sales for resale:

Wholesale 511 691

Bulk power and other 1,626 1,378

Other 13 14

Total 8,287 8,257

Utility retail electric customers (at March 31)

Residential 862,149 856,212

Commercial 146,914 146,333

Industrial 2,371 2,363

Total 1,011,434 1,004,908

Utility gas sold and transported (000s of dekatherms)

Residential 13,172 14,039

Commercial 8,475 8,965

Industrial 839 818

Retail subtotal 22,486 23,822

Transportation / other 32,813 31,006

Total 55,299 54,828

Utility retail gas customers (at March 31)

Residential 388,590 386,261

Commercial 45,529 45,326

Industrial 314 316

Total 434,433 431,903

Estimated operating income decreases from impacts of temperatures (in millions) -

Three Months Ended March 31,

2026 2025

Electric ($10) ($6)

Gas (6) (3)

Total temperature impact ($16) ($9)

Three Months Ended March 31,

2026 2025 Normal

Heating degree days (HDDs) (a)

Cedar Rapids, Iowa (IPL) 3,037 3,240 3,420

Madison, Wisconsin (WPL) 3,322 3,367 3,500

(a)HDDs are calculated using a simple average of the high and low temperatures each day compared to a 65 degree base. Normal degree days are calculated using a rolling 20-year average of historical HDDs.

GRAPHIC

Filename: alliantenergylogo.jpg · Sequence: 7

Binary file (408716 bytes)

Download alliantenergylogo.jpg

XML — IDEA: XBRL DOCUMENT

XML

Filename: R1.htm · Sequence: 9

v3.26.1

Document and Entity Information

Apr. 30, 2026

Entity Information [Line Items]

Document Type

8-K

Document Period End Date

Apr. 30, 2026

Entity Registrant Name

ALLIANT ENERGY CORP

Entity Central Index Key

0000352541

Amendment Flag

false

Entity Incorporation, State or Country Code

Entity Address, Address Line One

4902 N. Biltmore Lane

Entity Address, City or Town

Madison

Entity Address, State or Province

Entity Address, Postal Zip Code

53718

City Area Code

608

Local Phone Number

458-3311

Entity File Number

1-9894

Entity Tax Identification Number

39-1380265

Written Communications

false

Soliciting Material

false

Pre-commencement Tender Offer

false

Pre-commencement Issuer Tender Offer

false

Title of 12(b) Security

Common Stock, $0.01 Par Value

Trading Symbol

LNT

Security Exchange Name

NASDAQ

Entity Emerging Growth Company

false

IPL [Member]

Entity Information [Line Items]

Entity Registrant Name

INTERSTATE POWER & LIGHT CO

Entity Central Index Key

0000052485

Entity Incorporation, State or Country Code

Entity Address, Address Line One

Alliant Energy Tower

Entity Address, City or Town

Cedar Rapids

Entity Address, State or Province

Entity Address, Postal Zip Code

52401

City Area Code

319

Local Phone Number

786-4411

Entity File Number

1-4117

Entity Tax Identification Number

42-0331370

Entity Emerging Growth Company

false

WPL [Member]

Entity Information [Line Items]

Entity Registrant Name

WISCONSIN POWER & LIGHT CO

Entity Central Index Key

0000107832

Entity Incorporation, State or Country Code

Entity Address, Address Line One

4902 N. Biltmore Lane

Entity Address, City or Town

Madison

Entity Address, State or Province

Entity Address, Postal Zip Code

53718

City Area Code

608

Local Phone Number

458-3311

Entity File Number

0-337

Entity Tax Identification Number

39-0714890

Entity Emerging Growth Company

false

- Definition

Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.

+ References

No definition available.

+ Details

Name:

dei_AmendmentFlag

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Area code of city

+ References

No definition available.

+ Details

Name:

dei_CityAreaCode

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD.

+ References

No definition available.

+ Details

Name:

dei_DocumentPeriodEndDate

Namespace Prefix:

dei_

Data Type:

xbrli:dateItemType

Balance Type:

Period Type:

duration

- Definition

The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.

+ References

No definition available.

+ Details

Name:

dei_DocumentType

Namespace Prefix:

dei_

Data Type:

dei:submissionTypeItemType

Balance Type:

Period Type:

duration

- Definition

Address Line 1 such as Attn, Building Name, Street Name

+ References

No definition available.

+ Details

Name:

dei_EntityAddressAddressLine1

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Name of the City or Town

+ References

No definition available.

+ Details

Name:

dei_EntityAddressCityOrTown

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Code for the postal or zip code

+ References

No definition available.

+ Details

Name:

dei_EntityAddressPostalZipCode

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Name of the state or province.

+ References

No definition available.

+ Details

Name:

dei_EntityAddressStateOrProvince

Namespace Prefix:

dei_

Data Type:

dei:stateOrProvinceItemType

Balance Type:

Period Type:

duration

- Definition

A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityCentralIndexKey

Namespace Prefix:

dei_

Data Type:

dei:centralIndexKeyItemType

Balance Type:

Period Type:

duration

- Definition

Indicate if registrant meets the emerging growth company criteria.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityEmergingGrowthCompany

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.

+ References

No definition available.

+ Details

Name:

dei_EntityFileNumber

Namespace Prefix:

dei_

Data Type:

dei:fileNumberItemType

Balance Type:

Period Type:

duration

- Definition

Two-character EDGAR code representing the state or country of incorporation.

+ References

No definition available.

+ Details

Name:

dei_EntityIncorporationStateCountryCode

Namespace Prefix:

dei_

Data Type:

dei:edgarStateCountryItemType

Balance Type:

Period Type:

duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:

dei_EntityInformationLineItems

Namespace Prefix:

dei_

Data Type:

xbrli:stringItemType

Balance Type:

Period Type:

duration

- Definition

The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityRegistrantName

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityTaxIdentificationNumber

Namespace Prefix:

dei_

Data Type:

dei:employerIdItemType

Balance Type:

Period Type:

duration

- Definition

Local phone number for entity.

+ References

No definition available.

+ Details

Name:

dei_LocalPhoneNumber

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 13e

-Subsection 4c

+ Details

Name:

dei_PreCommencementIssuerTenderOffer

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 14d

-Subsection 2b

+ Details

Name:

dei_PreCommencementTenderOffer

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Title of a 12(b) registered security.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b

+ Details

Name:

dei_Security12bTitle

Namespace Prefix:

dei_

Data Type:

dei:securityTitleItemType

Balance Type:

Period Type:

duration

- Definition

Name of the Exchange on which a security is registered.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection d1-1

+ Details

Name:

dei_SecurityExchangeName

Namespace Prefix:

dei_

Data Type:

dei:edgarExchangeCodeItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as soliciting material pursuant to Rule 14a-12 under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 14a

-Subsection 12

+ Details

Name:

dei_SolicitingMaterial

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Trading symbol of an instrument as listed on an exchange.

+ References

No definition available.

+ Details

Name:

dei_TradingSymbol

Namespace Prefix:

dei_

Data Type:

dei:tradingSymbolItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as written communications pursuant to Rule 425 under the Securities Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Securities Act

-Number 230

-Section 425

+ Details

Name:

dei_WrittenCommunications

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Details

Name:

dei_LegalEntityAxis=lnt_IplMember

Namespace Prefix:

Data Type:

Balance Type:

Period Type:

- Details

Name:

dei_LegalEntityAxis=lnt_WplMember

Namespace Prefix:

Data Type:

Balance Type:

Period Type: