ALLIANT ENERGY CORP

NOTE 8. DEBT

NOTE 8(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2025, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2030, totaled $1.3 billion ($550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):

NOTE 8(b)Long-Term Debt -Long-term debt, net as of December 31 was as follows (dollars in millions):

(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.

(b)In May 2025, IPL issued $600 million of 5.6% senior debentures due 2035. A portion of the net proceeds was used for the retirement of IPL’s $50 million 5.5% senior debentures and $250 million 3.4% senior debentures. The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes. In September 2025, IPL issued $300 million of 5.6% senior debentures due 2055. The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.

(c)In December 2025, WPL issued $300 million of 5.7% debentures due 2055. The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.

(d)In March 2025, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 14 for information on AEF’s related interest rate swap. In January 2026, AEF retired its $300 million term loan.

(e)Refer to “Convertible Senior Notes” below for additional information.

(f)In September 2025, Alliant Energy issued $725 million of junior subordinated notes due 2056. The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S. Treasury rate plus a spread of 2.077%, provided the interest rate will not reset below 5.75%. The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes. Long term debt to be retired includes AEF’s $300 million variable rate term loan which was retired in January 2026, AEF’s $200 million of 1.4% senior notes and Alliant Energy’s $575 million of 3.875% convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity. Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.

(g)There were no significant sinking fund requirements related to the outstanding long-term debt.