ALLIANT ENERGY CORP

NOTE 8. INCOME TAXES

Income Tax Rates -Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy’s effective income tax rate for the three months ended March 31, 2026 was also impacted by changes in state income tax apportionment.

Deferred Tax Assets and Liabilities -

Carryforwards -At March 31, 2026, the carryforwards and expiration dates were estimated as follows (in millions):

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. 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.