Important September 2026 Tax Deadlines for Individuals and Businesses

September brings several important tax deadlines for individuals and businesses. Whether you make quarterly estimated tax payments or requested an extension for a 2025 tax return, here are a few dates to keep on your radar.

September 15, 2026

Third Quarter Estimated Tax Payments

If you are self-employed, own a business, have significant investment income, or otherwise do not have enough federal income tax withheld throughout the year, your third-quarter 2026 estimated tax payment is due September 15.

Estimated tax payments are generally required when your withholding and other tax payments will not be sufficient to cover your expected tax liability.

If your income has changed significantly during 2026, this is also a good time to review your projections. A change in business income, investment income, retirement distributions, or other sources of income could mean your estimated payments should be adjusted.

Extended S Corporation Returns

Calendar-year S corporations that requested an automatic six-month extension must file their 2025 Form 1120-S by September 15.

The corporation must also provide each shareholder with a Schedule K-1 reporting their share of the corporation's income, deductions, credits, and other tax items.

Remember that an extension provides additional time to file the return, but it does not extend the time to pay any tax that may have been due.

Extended Partnership Returns

Calendar-year partnerships that requested an automatic six-month extension must also file their 2025 Form 1065 by September 15.

Each partner should receive a Schedule K-1 reporting their share of the partnership's tax information.

September 30, 2026

Extended Trust and Estate Returns

Calendar-year trusts and estates that requested an automatic 5½-month extension must file their 2025 Form 1041 by September 30.

As with other extensions, the additional time applies to filing the return and does not extend the original deadline for paying any tax due.

Don't Let a Tax Deadline Sneak Up on You

Tax deadlines can be easy to overlook, particularly when you're focused on running a business or managing everything else life brings your way.

If we are currently preparing an extended return for you, our team is working with these deadlines in mind. However, if you believe you need to make a third-quarter estimated tax payment and aren't sure how much to pay, please contact our office as soon as possible.

Taking a few minutes to review your tax situation now can help reduce surprises—and potentially penalties—when tax season arrives.