September 15 is approaching, but seeing “estimated tax payment due” on the calendar doesn’t automatically mean you need to send the IRS money. For millions of freelancers, business owners, investors and others who receive income without sufficient tax withholding, however, it can be an important deadline. The third estimated-tax payment for the 2026 tax year is due Tuesday, September 15, and generally corresponds to income received from June 1 through August 31. The key question isn’t whether you call yourself self-employed or whether you have a W-2—it is whether you’ve paid enough federal tax during the year. Before automatically making a payment or ignoring the deadline, here’s how to figure out whether September 15 actually matters to you.
