Interstate Power & Light Co. Announces $500M Senior Debentures Offering

What Happened
Interstate Power & Light Company (IPL), a subsidiary of Alliant Energy Corporation, filed an 8-K reporting that on August 18, 2026 it entered into an Underwriting Agreement to sell $500 million aggregate principal amount of 5.100% Senior Debentures due 2031. The debentures were priced on August 18, 2026 and the offering is expected to close, subject to customary conditions, on August 21, 2026. The securities are being issued under an existing Indenture and were registered on Form S-3 (Registration No. 333-276062-01); a Prospectus Supplement was filed August 18, 2026.

Key Details

• Offering size: $500,000,000 in aggregate principal amount.
• Coupon and maturity: 5.100% interest, due 2031.
• Timing: Underwriting Agreement dated August 18, 2026; expected close August 21, 2026 (subject to standard closing conditions).
• Process and filings: Registered under IPL’s Form S-3; Prospectus Supplement filed Aug 18, 2026; press release announcing pricing filed as an exhibit.
• Legal opinions: Counsel opinions regarding legality and Iowa law were provided and filed with the 8-K.

Why It Matters
This transaction will increase IPL’s long-term funded debt by $500 million at a fixed 5.100% coupon upon closing, which affects interest obligations and consolidated capital structure for IPL and could influence Alliant Energy’s consolidated financial metrics. The registration on Form S-3 and the underwriting agreement indicate the offering was conducted as a public, underwritten debt issuance and was legally reviewed by outside counsel. The filing does not state the use of proceeds.