Alliant Energy LNT · USD

SEGMENTS OF BUSINESSAlliant Energy - Alliant Energy’s two reportable segments as of December 31, 2025 are:•IPL - is a utility primarily serving electric and natural gas customers in Iowa, and is its own reportable segment as shown in the tables below.•WPL - is a utility serving electric and natural gas customers in Wisconsin, and is its own reportable segment as shown in the tables below.Other, which is not a reportable segment of Alliant Energy, includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF is comprised of Alliant Energy’s interest in ATC Holdings, Travero, a non-utility wind farm, corporate venture investments, the Sheboygan Falls Energy Facility and other non-utility holdings. The “Other” columns are included in the tables below to reconcile to consolidated amounts. Prior to December 31, 2024, reportable segments for Alliant Energy’s, IPL’s, and WPL’s utility business were electric operations, gas operations, and other. In the fourth quarter of 2024, Alliant Energy, IPL and WPL adopted the FASB’s accounting standard for improvements to reportable segment disclosures. Previously reported information for prior periods has been recast to conform with the current period presentation. Alliant Energy’s chief operating decision maker (CODM) is its President and CEO, and IPL’s and WPL’s CODM is their CEO. The CODM uses net income generated from IPL’s and WPL’s operations to assess segment performance, make operating decisions, and allocate resources. Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. There was no single customer whose revenues were 10% or more of Alliant Energy’s, IPL’s and WPL’s respective consolidated revenues. All of Alliant Energy’s, IPL’s and WPL’s operations and assets are located in the U.S.

REVENUESRevenues from Alliant Energy’s, IPL’s and WPL’s utility businesses are primarily from electric and gas sales provided to customers based on approved tariffs or specific contracts with customers. IPL’s and WPL’s primary performance obligations under such arrangements are to deliver electricity and gas, and their customers simultaneously receive and consume the electricity and gas. For such arrangements, revenues are recognized equivalent to the value of the electricity or gas supplied during each period, including amounts billed during each period and changes in amounts estimated to be billed at the end of each period. IPL and WPL apply the right to invoice method to measure progress towards completing performance obligations to transfer electricity and gas to their customers.IPL provides retail electric and gas service to customers in Iowa, and WPL provides retail and wholesale electric and retail gas service to customers in Wisconsin. IPL also provides electricity to wholesale customers in Illinois and Iowa. IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired in July 2025. IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa through 2025.IPL’s and WPL’s retail electric and gas revenues include sales to residential, commercial and industrial customers. IPL’s and WPL’s retail electric and gas customer prices are based on IPL’s and WPL’s cost of service and are determined through general rate review proceedings and various tariff filings with the IUC and PSCW, respectively. Such tariff-based services provide electricity or gas to customers without a defined contractual term.IPL and WPL have wholesale electric market-based rate authority from FERC allowing them to participate in wholesale energy markets (e.g. MISO) and transact directly with third parties. This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values. FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings.

COMMITMENTS AND CONTINGENCIES(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility, and repowering projects at WPL’s Bent Tree Energy Facility. At December 31, 2025, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2026 for these projects were $459 million, $302 million, and $155 million, respectively.(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):Alliant Energy20262027202820292030ThereafterTotalNatural gas$271$191$163$145$103$245$1,118Coal764228———146Other (a)571684317105$404$249$199$149$106$262$1,369IPL20262027202820292030ThereafterTotalNatural gas$149$105$85$70$31$52$492Coal341410———58Other (a)2422221648$207$121$97$72$33$68$598WPL20262027202820292030ThereafterTotalNatural gas$122$86$78$75$72$193$626Coal422818———88Other (a)251————26$189$115$96$75$72$193$740(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2025.(c) Legal Proceedings - Alliant Energy, IPL and WPL are involved in legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations.(d) Guarantees and Indemnifications -Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company.

DEBT(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2025, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2030, totaled $1.3 billion ($550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):Alliant EnergyIPLWPLDecember 31202520242025202420252024Amount outstanding$88$558$88$50$—$183Weighted average interest rates3.8%4.5%3.8%4.6%N/A4.5%Available credit facility capacity$1,212$742$262$250$400$217Alliant EnergyIPLWPLFor the year ended202520242025202420252024Maximum amount outstanding (based on daily outstanding balances)$741$632$141$80$297$390Average amount outstanding (based on daily outstanding balances)$349$327$25$1$176$70Weighted average interest rates4.5%5.3%4.6%5.1%4.5%5.4%(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):20252024Alliant EnergyIPLWPLAlliant EnergyIPLWPLSenior Debentures (a):4.1%, due 2028$500 $500 $— $500 $500 $— 3.6%, due 2029 300 300 — 300 300 — 2.3%, due 2030400 400 — 400 400 — 5.7%, due 2033300 300 — 300 300 — 6.45%, due 2033100 100 — 100 100 — 4.95%, due 2034350 350 — 350 350 — 6.3%, due 2034125 125 — 125 125 — 5.6%, due 2035 (b)600 600 — — — — 6.25%, due 2039300 300 — 300 300 — 4.7%, due 2043250 250 — 250 250 — 3.7%, due 2046 300 300 — 300 300 — 3.5%, due 2049 300 300 — 300 300 — 3.1%, due 2051300 300 — 300 300 — 5.45%, due 2054300 300 — 300 300 — 5.6%, due 2055 (b)300 300 — — — — 3.4%, (Retired in 2025)— — — 250 250 — 5.5%, (Retired in 2025)— — — 50 50 — 4,725 4,725 — 4,125 4,125 — Debentures (a):3.05%, due 2027300 — 300 300 — 300 3%, due 2029 350 — 350 350 — 350 1.95%, due 2031300 — 300 300 — 300 3.95%, due 2032600 — 600 600 — 600 4.95%, due 2033300 — 300 300 — 300 5.375%, due 2034300 — 300 300 — 300 6.25%, due 2034100 — 100 100 — 100 6.375%, due 2037300 — 300 300 — 300 7.

INCOME TAXESIncome Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):Alliant EnergyIPLWPL202520242023202520242023202520242023Current tax expense (benefit):Federal$10$13($3)($21)($19)($44)$38$37$48State(1)(10)(6)(10)(19)(21)182325Deferred tax expense (benefit):Federal5960100363887302410State3315362(17)171673Production tax credits(208)(177)(121)(133)(108)(95)(75)(69)(26)Investment tax credits(42)(15)(1)(1)(4)(1)(41)(11)—Provision recorded as a change in accrued interest——(1)——(1)———($149)($114)$4($127)($129)($58)($14)$11$60Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2. In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures. Previously reported information for prior periods has been recast to conform with current period presentation.

LEASESOperating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions):December 31, 2025December 31, 2024Alliant EnergyIPLWPLAlliant EnergyIPLWPLProperty, plant and equipment, net$21$11$9$22$12$9Other current liabilities$2$1$1$2$1$1Other liabilities1910820118Total operating lease liabilities$21$11$9$22$12$9Weighted average remaining lease term10 years10 years11 years11 years11 years12 yearsWeighted average discount rate4%4%4%4%4%4%Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced. The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities. The leases do not contain purchase options and are fixed lease payments.

Cybersecurity risks are identified as key risks through the enterprise risk management (ERM) program. These risks could include use of malicious code, employee theft or misuse, advanced persistent threats, vulnerabilities, fraud attempts, and phishing attacks that could cause, among others, an operations or information technology system failure, or breach or loss of sensitive information. The potential impact of cybersecurity risks on our business operations, results of operations or financial condition is discussed in the “Risks Related to Business Operations” section of Item 1A “Risk Factors.” We have not had any material cybersecurity breaches or incidents and have not incurred any material expenses, penalties or settlement costs related to any cybersecurity breaches or incidents. However, measures that we take to avoid, detect, mitigate or recover from cybersecurity breaches or incidents may be insufficient or become ineffective, and there are no assurances that cybersecurity breaches or incidents will not impact our business operations and strategy, results of operations and financial condition.We maintain a cybersecurity program that includes development and implementation of policies, procedures and tools designed to help ensure availability of critical operations, information technology and telecommunication systems and safeguard sensitive information. The cybersecurity program is assessed against industry standards, including the National Institute of Standards and Technology Cybersecurity Framework. This assessment is conducted by a third party periodically and internally at least annually. We are also required to comply with cybersecurity standards under the North American Electric Reliability Corporation (NERC) Critical Infrastructure Protection and by the Department of Homeland Security Transportation Security Administration. We also periodically collaborate with federal and state law enforcement experts, external assessors, consultants, industry peers and other third parties in connection with understanding market and threat conditions used to identify, assess and mitigate cybersecurity risks.

INVESTMENTSUnconsolidated Equity Investments - Alliant Energy’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):Ownership Interest atCarrying Value at December 31,Equity (Income) / LossDecember 31, 202520252024202520242023ATC Holdings16%, 20%$463$415($59)($57)($49)Non-utility wind farm in Oklahoma50%112107(9)(6)(7)Corporate venture investmentsVarious7678103(2)OtherVarious2323(2)(1)(3)$674$623($60)($61)($61)Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):Alliant Energy202520242023Revenues$1,080$1,005$898Operating income482433384Net income91434370As of December 31:Current assets254223Non-current assets10,8189,930Current liabilities879524Non-current liabilities4,2433,933Noncontrolling interest184221ATC Holdings - As of December 31, 2025, Alliant Energy has a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, collectively referred to as ATC Holdings. ATC is an independent, for-profit, transmission-only company. ATC Holdco LLC holds an interest in Duke-American Transmission Company, LLC, which holds a note receivable related to previously owned electric transmission infrastructure in North America.Non-utility Wind Farm in Oklahoma - The non-utility wind farm located in Oklahoma provides electricity to a third-party under a long-term PPA, and has both cash and tax equity ownership. Alliant Energy does not maintain or operate the wind farm, and provided a parent guarantee of its subsidiary’s indemnification obligations under the operating agreement and PPA. Refer to Note 16(d) for discussion of the guarantee.Corporate Venture Investments - Alliant Energy has various minority ownership interests in regional and national venture funds, including a global coalition of energy companies working together to help identify and research innovative technologies and business models within the emerging energy economy.