NorthWestern Energy Group Inc 2025年度报告

(Mark One) ANNUAL REPORT PURSUANT TO SECTION13 OR 15(d)OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2025 OR ☐TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d)OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period fromto Commission File Number: 000-56598 NORTHWESTERN ENERGY GROUP, INC. (Exact name of registrant as specified in its charter) Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. YesNo Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. YesNo Indicate by check mark whether the registrant (1)has filed all reports required to be filed by Section13 or 15(d)of the Securities Exchange Act of 1934 during thepreceding 12months (or for such shorter period that the registrant was required to file such reports), and (2)has been subject to such filing requirements for the past 90days. YesNo Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T(§ 232.405 of this chapter) during the preceding 12 months (or for shorter period that the registrant was required to submit such files). YesNo Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growthcompany.See the definitions of “large accelerated filer,” “accelerated filer”, “smaller reporting company”, and "emerging growth company" inRule12b-2 of the Exchange Act. Large Accelerated FilerAccelerated Filer☐Non-accelerated Filer☐Smaller Reporting Company☐Emerging Growth Company☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new orrevised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. YesNo Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal controlover financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issuedits audit report. If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filingreflect the correction of an error to the previously issued financial statements. Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received byany of the registrant's executive officers during the relevant recovery period pursuant to§240.10D-1(b). Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes☐No The aggregate market value of the voting and non-voting common stock held by nonaffiliates of the registrant was $3,149,159,359 computed using the lastsales price of $51.30 per share of the registrant’s common stock on June30, 2025, the last business day of the registrant’s most recently completed secondfiscal quarter. As of February6, 2026, 61,443,621 shares of the registrant’s common stock, par value $0.01 per share, were outstanding. Documents Incorporated by ReferenceCertain sections of our Proxy Statement for the 2026 Annual Meeting of Shareholders are incorporated by reference into Part III of this Form 10-K PartII Item 5Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities50Item 6[Reserved]50Item 7Management’s Discussion and Analysis of Financial Condition and Results of Operations51Item 7AQuantitative and Qualitative Disclosures About Market Risk75Item 8Financial Statements and Supplementary Data75Item 9Changes In and Disagreements With Accountants on Accounting and Financial Disclosure76Item 9AControls and Procedures76Item 9BOther Information76Item 9CDisclosure Regarding Foreign Jurisdictions that Prevent Inspections76 On one or more occasions, we may make statements in this Annual Report on Form 10-K regarding our assumptions, projections,expectations, targets, intentions or beliefs about future events. All statements other than statements of historical facts, included orincorporated by reference in this Annual Report, relating to our current expectations of future financial performance, continuedgrowth, changes in economic conditions or capital markets, changes in customer usage patterns and preferences, and statementsrelating to our pending merger with Black Hills Corporation are forward-looking statements within the meaning of Section 27A of theSecurities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Words or phrases such as “anticipates," “may," “will," “should," “believes," “es