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Income Taxes | 12 Months Ended
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Dec. 31, 2024
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $13 |  | ($3) |  | $7 |  | ($19) |  | ($44) |  | ($29) |  | $37 |  | $48 |  | $46
State | (10) |  | (6) |  | 2 |  | (19) |  | (21) |  | (8) |  | 23 |  | 25 |  | 16
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 60 |  | 100 |  | 109 |  | 38 |  | 87 |  | 91 |  | 24 |  | 10 |  | 10
State | 15 |  | 36 |  | 28 |  | (17) |  | 17 |  | 1 |  | 7 |  | 3 |  | 12
Production tax credits | (177) |  | (121) |  | (123) |  | (108) |  | (95) |  | (105) |  | (69) |  | (26) |  | (18)
Investment tax credits | (15) |  | (1) |  | (1) |  | (4) |  | (1) |  | — |  | (11) |  | — |  | —
Provision recorded as a change in accrued interest | — |  | (1) |  | — |  | — |  | (1) |  | — |  | — |  | — |  | —
| ($114) |  | $4 |  | $22 |  | ($129) |  | ($58) |  | ($50) |  | $11 |  | $60 |  | $66
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. 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 Generation Station discussed in Note 2.
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Statutory federal income tax rate | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21%
State income taxes, net of federal benefits | (1) |  | 2 |  | 3 |  | (12) |  | (2) |  | (2) |  | 6 |  | 5 |  | 6
Production tax credits | (31) |  | (17) |  | (18) |  | (46) |  | (31) |  | (34) |  | (20) |  | (7) |  | (5)
Investment tax credits | (3) |  | — |  | — |  | (2) |  | — |  | — |  | (3) |  | — |  | —
Amortization of excess deferred taxes (Refer to Note 2) | (2) |  | (2) |  | (2) |  | (5) |  | (2) |  | (2) |  | — |  | (2) |  | (3)
Effect of rate-making on property-related differences | (5) |  | (4) |  | (1) |  | (10) |  | (5) |  | (1) |  | (1) |  | (3) |  | (2)
Other items, net | 1 |  | 1 |  | — |  | (1) |  | — |  | 2 |  | — |  | 1 |  | —
Overall income tax rate | (20%) |  | 1% |  | 3% |  | (55%) |  | (19%) |  | (16%) |  | 3% |  | 15% |  | 17%
Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,596 |  |  | $2,453 |  |  | $1,521 |  |  | $1,415 |  |  | $999 |  |  | $972 |
ATC Holdings | 135 |  |  | 127 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 178 |  |  | 213 |  |  | 120 |  |  | 157 |  |  | 66 |  |  | 64 |
Total deferred tax liabilities | 2,909 |  |  | 2,793 |  |  | 1,641 |  |  | 1,572 |  |  | 1,065 |  |  | 1,036 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 605 |  |  | 649 |  |  | 426 |  |  | 449 |  |  | 166 |  |  | 191 |
Net operating losses carryforwards - state | 20 |  |  | 26 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Other | 98 |  |  | 79 |  |  | 37 |  |  | 32 |  |  | 34 |  |  | 19 |
Subtotal deferred tax assets | 723 |  |  | 754 |  |  | 464 |  |  | 482 |  |  | 200 |  |  | 210 |
Valuation allowances | (2) |  |  | (3) |  |  | (2) |  |  | (1) |  |  | — |  |  | (1) |
Total deferred tax assets | 721 |  |  | 751 |  |  | 462 |  |  | 481 |  |  | 200 |  |  | 209 |
Total deferred tax liabilities, net | $2,188 |  |  | $2,042 |  |  | $1,179 |  |  | $1,091 |  |  | $865 |  |  | $827 |
Carryforwards - At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2044 |  | $338 |  | $7 |  | $1
Federal tax credits | 2033-2044 |  | 605 |  | 426 |  | 166
Valuation Allowances - Refer to N ote 1(c) for discussion of valuation allowances related to the expected transfer of renewable tax credits to other corporate taxpayers. Uncertain Tax Positions - At December 31, 2024, 2023 and 2022, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2024, no material changes to unrecognized tax benefits are expected during the next 12 months. Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2021 | - | 2023
Consolidated Iowa income tax returns (b) | 2021 | - | 2023
Wisconsin combined tax returns (c) | 2020 | - | 2023
(a)The 2021 and 2022 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b)The statute of limitations for these Iowa tax returns expires three years from each filing date. (c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date. Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if the minimum receipt threshold is met. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In 2022 and 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. In addition, Iowa tax reform made Iowa state income taxes fully deductible for the purpose of determining Iowa state income tax obligations beginning with the 2023 tax year. Alliant Energy reflected the deduction of the additional Iowa state income taxes in its 2023 Iowa state income tax return filed in 2024, which resulted in a $26 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2024. The reductions in tax-related regulatory assets are expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $8 million, $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022, 2023 and 2024, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
IPL [Member] |
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $13 |  | ($3) |  | $7 |  | ($19) |  | ($44) |  | ($29) |  | $37 |  | $48 |  | $46
State | (10) |  | (6) |  | 2 |  | (19) |  | (21) |  | (8) |  | 23 |  | 25 |  | 16
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 60 |  | 100 |  | 109 |  | 38 |  | 87 |  | 91 |  | 24 |  | 10 |  | 10
State | 15 |  | 36 |  | 28 |  | (17) |  | 17 |  | 1 |  | 7 |  | 3 |  | 12
Production tax credits | (177) |  | (121) |  | (123) |  | (108) |  | (95) |  | (105) |  | (69) |  | (26) |  | (18)
Investment tax credits | (15) |  | (1) |  | (1) |  | (4) |  | (1) |  | — |  | (11) |  | — |  | —
Provision recorded as a change in accrued interest | — |  | (1) |  | — |  | — |  | (1) |  | — |  | — |  | — |  | —
| ($114) |  | $4 |  | $22 |  | ($129) |  | ($58) |  | ($50) |  | $11 |  | $60 |  | $66
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. 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 Generation Station discussed in Note 2.
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Statutory federal income tax rate | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21%
State income taxes, net of federal benefits | (1) |  | 2 |  | 3 |  | (12) |  | (2) |  | (2) |  | 6 |  | 5 |  | 6
Production tax credits | (31) |  | (17) |  | (18) |  | (46) |  | (31) |  | (34) |  | (20) |  | (7) |  | (5)
Investment tax credits | (3) |  | — |  | — |  | (2) |  | — |  | — |  | (3) |  | — |  | —
Amortization of excess deferred taxes (Refer to Note 2) | (2) |  | (2) |  | (2) |  | (5) |  | (2) |  | (2) |  | — |  | (2) |  | (3)
Effect of rate-making on property-related differences | (5) |  | (4) |  | (1) |  | (10) |  | (5) |  | (1) |  | (1) |  | (3) |  | (2)
Other items, net | 1 |  | 1 |  | — |  | (1) |  | — |  | 2 |  | — |  | 1 |  | —
Overall income tax rate | (20%) |  | 1% |  | 3% |  | (55%) |  | (19%) |  | (16%) |  | 3% |  | 15% |  | 17%
Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,596 |  |  | $2,453 |  |  | $1,521 |  |  | $1,415 |  |  | $999 |  |  | $972 |
ATC Holdings | 135 |  |  | 127 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 178 |  |  | 213 |  |  | 120 |  |  | 157 |  |  | 66 |  |  | 64 |
Total deferred tax liabilities | 2,909 |  |  | 2,793 |  |  | 1,641 |  |  | 1,572 |  |  | 1,065 |  |  | 1,036 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 605 |  |  | 649 |  |  | 426 |  |  | 449 |  |  | 166 |  |  | 191 |
Net operating losses carryforwards - state | 20 |  |  | 26 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Other | 98 |  |  | 79 |  |  | 37 |  |  | 32 |  |  | 34 |  |  | 19 |
Subtotal deferred tax assets | 723 |  |  | 754 |  |  | 464 |  |  | 482 |  |  | 200 |  |  | 210 |
Valuation allowances | (2) |  |  | (3) |  |  | (2) |  |  | (1) |  |  | — |  |  | (1) |
Total deferred tax assets | 721 |  |  | 751 |  |  | 462 |  |  | 481 |  |  | 200 |  |  | 209 |
Total deferred tax liabilities, net | $2,188 |  |  | $2,042 |  |  | $1,179 |  |  | $1,091 |  |  | $865 |  |  | $827 |
Carryforwards - At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2044 |  | $338 |  | $7 |  | $1
Federal tax credits | 2033-2044 |  | 605 |  | 426 |  | 166
Valuation Allowances - Refer to N ote 1(c) for discussion of valuation allowances related to the expected transfer of renewable tax credits to other corporate taxpayers. Uncertain Tax Positions - At December 31, 2024, 2023 and 2022, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2024, no material changes to unrecognized tax benefits are expected during the next 12 months. Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2021 | - | 2023
Consolidated Iowa income tax returns (b) | 2021 | - | 2023
Wisconsin combined tax returns (c) | 2020 | - | 2023
(a)The 2021 and 2022 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b)The statute of limitations for these Iowa tax returns expires three years from each filing date. (c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date. Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if the minimum receipt threshold is met. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In 2022 and 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. In addition, Iowa tax reform made Iowa state income taxes fully deductible for the purpose of determining Iowa state income tax obligations beginning with the 2023 tax year. Alliant Energy reflected the deduction of the additional Iowa state income taxes in its 2023 Iowa state income tax return filed in 2024, which resulted in a $26 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2024. The reductions in tax-related regulatory assets are expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $8 million, $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022, 2023 and 2024, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
WPL [Member] |
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $13 |  | ($3) |  | $7 |  | ($19) |  | ($44) |  | ($29) |  | $37 |  | $48 |  | $46
State | (10) |  | (6) |  | 2 |  | (19) |  | (21) |  | (8) |  | 23 |  | 25 |  | 16
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 60 |  | 100 |  | 109 |  | 38 |  | 87 |  | 91 |  | 24 |  | 10 |  | 10
State | 15 |  | 36 |  | 28 |  | (17) |  | 17 |  | 1 |  | 7 |  | 3 |  | 12
Production tax credits | (177) |  | (121) |  | (123) |  | (108) |  | (95) |  | (105) |  | (69) |  | (26) |  | (18)
Investment tax credits | (15) |  | (1) |  | (1) |  | (4) |  | (1) |  | — |  | (11) |  | — |  | —
Provision recorded as a change in accrued interest | — |  | (1) |  | — |  | — |  | (1) |  | — |  | — |  | — |  | —
| ($114) |  | $4 |  | $22 |  | ($129) |  | ($58) |  | ($50) |  | $11 |  | $60 |  | $66
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. 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 Generation Station discussed in Note 2.
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Statutory federal income tax rate | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21%
State income taxes, net of federal benefits | (1) |  | 2 |  | 3 |  | (12) |  | (2) |  | (2) |  | 6 |  | 5 |  | 6
Production tax credits | (31) |  | (17) |  | (18) |  | (46) |  | (31) |  | (34) |  | (20) |  | (7) |  | (5)
Investment tax credits | (3) |  | — |  | — |  | (2) |  | — |  | — |  | (3) |  | — |  | —
Amortization of excess deferred taxes (Refer to Note 2) | (2) |  | (2) |  | (2) |  | (5) |  | (2) |  | (2) |  | — |  | (2) |  | (3)
Effect of rate-making on property-related differences | (5) |  | (4) |  | (1) |  | (10) |  | (5) |  | (1) |  | (1) |  | (3) |  | (2)
Other items, net | 1 |  | 1 |  | — |  | (1) |  | — |  | 2 |  | — |  | 1 |  | —
Overall income tax rate | (20%) |  | 1% |  | 3% |  | (55%) |  | (19%) |  | (16%) |  | 3% |  | 15% |  | 17%
Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,596 |  |  | $2,453 |  |  | $1,521 |  |  | $1,415 |  |  | $999 |  |  | $972 |
ATC Holdings | 135 |  |  | 127 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 178 |  |  | 213 |  |  | 120 |  |  | 157 |  |  | 66 |  |  | 64 |
Total deferred tax liabilities | 2,909 |  |  | 2,793 |  |  | 1,641 |  |  | 1,572 |  |  | 1,065 |  |  | 1,036 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 605 |  |  | 649 |  |  | 426 |  |  | 449 |  |  | 166 |  |  | 191 |
Net operating losses carryforwards - state | 20 |  |  | 26 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Other | 98 |  |  | 79 |  |  | 37 |  |  | 32 |  |  | 34 |  |  | 19 |
Subtotal deferred tax assets | 723 |  |  | 754 |  |  | 464 |  |  | 482 |  |  | 200 |  |  | 210 |
Valuation allowances | (2) |  |  | (3) |  |  | (2) |  |  | (1) |  |  | — |  |  | (1) |
Total deferred tax assets | 721 |  |  | 751 |  |  | 462 |  |  | 481 |  |  | 200 |  |  | 209 |
Total deferred tax liabilities, net | $2,188 |  |  | $2,042 |  |  | $1,179 |  |  | $1,091 |  |  | $865 |  |  | $827 |
Carryforwards - At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2044 |  | $338 |  | $7 |  | $1
Federal tax credits | 2033-2044 |  | 605 |  | 426 |  | 166
Valuation Allowances - Refer to N ote 1(c) for discussion of valuation allowances related to the expected transfer of renewable tax credits to other corporate taxpayers. Uncertain Tax Positions - At December 31, 2024, 2023 and 2022, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2024, no material changes to unrecognized tax benefits are expected during the next 12 months. Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2021 | - | 2023
Consolidated Iowa income tax returns (b) | 2021 | - | 2023
Wisconsin combined tax returns (c) | 2020 | - | 2023
(a)The 2021 and 2022 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b)The statute of limitations for these Iowa tax returns expires three years from each filing date. (c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date. Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if the minimum receipt threshold is met. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In 2022 and 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. In addition, Iowa tax reform made Iowa state income taxes fully deductible for the purpose of determining Iowa state income tax obligations beginning with the 2023 tax year. Alliant Energy reflected the deduction of the additional Iowa state income taxes in its 2023 Iowa state income tax return filed in 2024, which resulted in a $26 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2024. The reductions in tax-related regulatory assets are expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $8 million, $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022, 2023 and 2024, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.

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