Tax Deadlines for September 15
Extended tax deadline due
September 15 is the filing deadline for 2010 tax returns for calendar-year corporations that received an extension of the March 15 filing deadline as well as the filing deadline for 2010 partnership tax returns that had an extension of the April 18 filing deadline.
3rd-quarter 2021 estimated tax payment due
If you're self-employed or have other income that requires you to pay quarterly estimated taxes, make sure your third-quarter payment is postmarked by September 15, 2021.