09/01/2026
September 15th isn’t just “another tax date.” If you’re self-employed, this one can actually cost you if you miss it
Here’s what’s due:
→ Q3 2026 estimated tax payment
→ Extended deadline for S-Corp and partnership returns
Miss the estimated payment and the IRS can charge you a penalty, even if you pay in full come April. Miss the extended business return deadline and it’s a flat penalty per month, per partner or shareholder, on top of whatever you already owe
Swipe through for exactly who this applies to and what to do before the 15th