Exhibit 99.1 Alliant Energy Corporation Corporate Headquarters 4902 North Biltmore Lane Madison, WI 53718-2148 www.alliantenergy.com News Release FOR IMMEDIATE RELEASE Media Hotline: (608) 458-4040 Investor Relations: Susan Gille (608) 458-3956 ALLIANT ENERGY ANNOUNCES FIRST QUARTER 2025 RESULTS MADISON, Wis. - May 8, 2025 - Alliant Energy Corporation (NASDAQ: LNT) today announced U.S. generally accepted accounting principles (GAAP) consolidated unaudited earnings per share (EPS) for the three months ended ...