ALLIANT ENERGY CORP

NOTE 8. INCOME TAXES

Income 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. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin), production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the three and nine months ended September 30, 2026 were additional tax credits during 2026 from renewable generation and energy storage projects previously placed in service, as well as projects currently expected to be placed in service during 2026. Alliant Energy’s effective income tax rate for the nine months ended September 30, 2026 was also impacted by changes in state income tax apportionment.

Deferred Tax Assets and Liabilities -

Carryforwards -At September 30, 2026, the carryforwards and expiration dates were estimated as follows (in millions):

(a)In October 2026, Alliant Energy, IPL and WPL transferred renewable tax credits to other corporate taxpayers for proceeds of $174 million, $107 million and $67 million, respectively.

State Income Tax Apportionment - Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state income tax apportionment. Estimates of state income tax apportionment are supported by historical data and reasonable projections. 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 and as a result, Alliant Energy expected an increase in total state income tax apportionment. Alliant Energy parent company’s deferred tax assets were remeasured, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in the third quarter of 2025. 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. Accordingly, Alliant Energy currently expects a decrease in Wisconsin state income tax apportionment and an increase in Iowa state income tax apportionment, primarily due to the change in projected electric utility revenues at WPL and IPL. Alliant Energy parent company’s deferred tax assets were remeasured to reflect the change in estimated state income tax apportionment, which resulted in a $12 million reduction to income tax expense in Alliant Energy’s income statement and a decrease in deferred tax liabilities on Alliant Energy’s balance sheet in the first quarter of 2026.