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Rate Matters (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2027 | Dec. 31, 2026 | Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | [2] | Dec. 31, 2022 | [2]
Fuel Rules [Abstract] |  |  |  |  |  |  |  |  |
Deferred fuel rules monitored costs |  |  |  | $ 7.1 | [1] | $ 3.0 | [2] | $ 7.2 | $ (8.8)
Electric Rate Proceeding [Member] | PSCW [Member] | MGE [Member] |  |  |  |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |  |  |  |
Authorized rate increase (decrease), percentage | [3],[5] |  |  | 2.63% | [4] | 1.54% |  |  |
Authorized return on equity, percentage |  |  |  | 9.70% |  | 9.70% |  |  |
Approved equity capital structure, percentage |  |  |  | 56.10% |  | 56.10% |  |  |
Fuel Rules [Abstract] |  |  |  |  |  |  |  |  |
Fuel rules, bandwidth |  |  |  | 2.00% |  | 2.00% |  |  |
Electric Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member] |  |  |  |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |  |  |  |
Authorized rate increase (decrease), percentage | [3],[6] | 3.63% | 0.15% |  |  |  |  |  |
Authorized return on equity, percentage |  | 9.80% | 9.80% |  |  |  |  |  |
Approved equity capital structure, percentage |  | 56.10% | 56.10% |  |  |  |  |  |
Gas Rate Proceeding [Member] | PSCW [Member] | MGE [Member] |  |  |  |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |  |  |  |
Authorized rate increase (decrease), percentage | [3],[5] |  |  | 1.32% |  | 2.44% |  |  |
Authorized return on equity, percentage |  |  |  | 9.70% |  | 9.70% |  |  |
Approved equity capital structure, percentage |  |  |  | 56.10% |  | 56.10% |  |  |
Gas Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member] |  |  |  |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |  |  |  |
Authorized rate increase (decrease), percentage | [3],[6] | 2.04% | 2.77% |  |  |  |  |  |
Authorized return on equity, percentage |  | 9.80% | 9.80% |  |  |  |  |  |
Approved equity capital structure, percentage |  | 56.10% | 56.10% |  |  |  |  |  |
[1] | These costs will be subject to the PSCW's annual review of 2025 fuel costs, expected to be completed in 2026.
[2] | There was no change to the refund or recovery in the fuel rules proceedings from the amount MGE deferred.
[3] | Includes an earnings sharing mechanism, under which, if MGE earns above the authorized Return on Equity (ROE) in the rate order: (i) MGE will retain 100.0% of earnings for the first 15 basis points above the authorized ROE; (ii) 50.0% of the next 60 basis points will be required to be deferred and returned to customers; and (iii) 100.0% of any remaining excess earnings will be required to be refunded to customers. The earnings calculation excludes fuel rules adjustments. See "Fuel Rules" below.
[4] | The PSCW approved a 2025 Fuel Cost Plan in December 2024. The plan lowered the 2025 increase in electric rates to 2.63% to reflect lower expected fuel costs.
[5] | The electric rate increase was driven by an increase in rate base including our investments made in West Riverside, local solar, continued investment in grid modernization, as well as higher costs for transmission, pension and other post retirement benefits, and uncollectible costs (including costs previously deferred from prior years). This increase in electric costs is offset by a decrease in fuel costs and benefit from lower tax expense (including impacts from the Inflation Reduction Act). MGE filed an updated 2025 fuel forecast with the PSCW in 2024, which impacted rates in 2025, based on any variance between the forecast submitted as part of the rates and updated forecast. In addition, the PSCW authorized MGE to defer a recovery of and a return on costs associated for any change in the in-service date for Paris and force majeure costs for Badger Hollow II and Paris that were not reflected in this rate filing. The PSCW also approved deferral of any differential in PTC tax credits reflected in rates and actual credits produced. These deferrals will be reflected in MGE's next rate case filing. The gas rate increases were also driven by our investment made in grid modernization and higher pension and other post retirement benefits and uncollectible costs (including costs previously deferred from prior years). This increase in gas costs is offset by a tax benefit related to excess deferred taxes. Included in the gas residential rate is a reduction in the customer fixed charge.
[6] | The electric rate increase reflects growth in rate base, primarily from investments in solar and battery projects, West Riverside, and continued investment in grid modernization, as well as higher costs for transmission. The increase in electric costs is offset by a decrease in fuel costs, changes in pension and other post retirement benefits, updated depreciation rates, and benefit from lower tax expense (including impacts from the Inflation Reduction Act). MGE will file an updated 2027 fuel forecast with the PSCW in 2026 which may impact rates in 2027, depending on any variance between the forecast submitted as a part of the proposed rates and updated forecast. The gas increase is driven by an increase in rate base including continued distribution infrastructure improvements designed to enhance reliability and safety and system modernization, and updated depreciation rates. The increase in gas costs is offset by changes in pension and other post retirement benefits.

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