September 15 Is a Major Tax Deadline – Who Actually Needs to Pay the IRS?

September 15, 2026, marks the third estimated federal tax payment deadline for many individuals, including taxpayers with self-employment or other income without sufficient withholding – Shutterstock

September 15 can sneak up on taxpayers because it does not involve the giant annual tax-day frenzy that surrounds April 15. Yet for millions of Americans, September 15 marks the deadline for the third estimated federal tax payment of 2026, and ignoring it could create an unpleasant surprise later.

The deadline generally matters to people who earn income without enough tax coming out of each paycheck, including many self-employed workers, investors and business owners. The good news? Plenty of taxpayers can happily leave September 15 alone.