ALLIANT ENERGY CORP

NOTE 3. PROPERTY, PLANT AND EQUIPMENT

At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):

(a)Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.

(b)WPL’s Grant County (100 MW) and Wood County (75 MW) energy storage facilities, and IPL’s Wever (99 MW) energy storage facility, were placed in service in 2025.

(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.

(d)Less accumulated amortization of $120 million and $116 million for WPL as of December 31, 2025 and 2024, respectively. Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.

(e)Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.

(f)Less accumulated depreciation of $81 million and $78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.

(g)Less accumulated depreciation of $305 million and $289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. The amount of AFUDC generated by equity and debt components was as follows (in millions):

Non-utility and Other - The non-utility and other property, plant and equipment recorded on Alliant Energy’s balance sheets include the following:

Non-utility Generation - The Sheboygan Falls Energy Facility was placed in service in 2005 and is depreciated using the straight-line method over a 45-year period.

Corporate Services and Other -Property, plant and equipment related to Corporate Services include computer software, and the corporate headquarters building located in Madison, Wisconsin. The majority of the software is amortized over a 5-year period. Other property, plant and equipment include Travero assets (a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; and a rail-served warehouse in Iowa). All Corporate Services and Other property, plant and equipment are depreciated using the straight-line method over periods ranging from 5 to 30 years.