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Taxes (Tables) | 6 Months Ended
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Jun. 30, 2026
Income Tax Disclosure [Abstract] |
Effective Tax Rate Reconciliation | The effective income tax rates for the period, computed by dividing income tax expense by income before taxes, were as follows:
|  | MGE Energy |  | MGE
Effective income tax rate |  | 2026 |  | 2025 |  | 2026 |  | 2025
Three Months Ended June 30, |  |  | 11.4 |  | % |  |  | 10.1 |  | % |  |  | 9.8 |  | % |  |  | 8.4 |  | %
Six Months Ended June 30, |  |  | 11.0 |  | % |  |  | 12.0 |  | % |  |  | 9.4 |  | % |  |  | 10.5 |  | %
The effective tax rates were different than the federal statutory rate primarily due to state income taxes, net of the related federal tax benefit, federal production tax credits (PTC) and investment tax credits (ITC), the amortization of excess deferred taxes, and the impact of non-taxable income related to the equity portion of Allowance for Funds Used During Construction (AFUDC), net of depreciation. For both MGE Energy and MGE, the decrease in the effective tax rate for the six months ended June 30, 2026, compared to the prior year period was driven primarily by additional federal tax credits associated with renewable generation and energy storage projects, as well as increased non-taxable income related to the equity portion of AFUDC on projects under construction.

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- Definition Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 231 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482663/740-10-55-231 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 12A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-12A Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-12 + Details
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