Did you file an extension for your 2025 tax return? If so, you are not alone. But now is the time to stop putting it off. For business filers who properly requested an extension, September 15, 2026, is the deadline to file 2025 1065 and 1120-S returns. Missing that deadline will be costly since IRS will assess a $200 per month penalty until the Return is filed. For taxpayers who properly requested an extension, October 15, 2026, is the deadline to file the 2025 federal income