Key September 2026 Business Tax Deadlines

September is here, bringing a fresh season and several important tax deadlines for businesses. Whether you are managing corporate estimated tax payments, finalizing extended returns for S corporations and partnerships, or handling employer payroll tax deposits, keeping a close eye on the calendar is essential. At Robertson Financial Group in Tucker, Georgia, we believe that staying ahead of your tax obligations is a powerful way to keep your operations running smoothly and confidently. Review the key due dates below to help keep your business filings and payments on track.

Business team reviewing financial documents

September 15: S Corporations

If your S corporation requested an automatic six-month extension, this is the deadline to file your 2025 calendar year income tax return (Form 1120-S) and pay any tax due. You must also provide each shareholder with a copy of their Schedule K-1 (Form 1120-S) or a substitute Schedule K-1. If applicable, you will also need to provide Schedule K-3 (Form 1120-S) or a substitute Schedule K-3 (Form 1120-S).

September 15: Corporations

Calendar year corporations must stay on top of their current-year tax liabilities by depositing the third installment of estimated income tax for 2026.

September 15: Partnerships

For partnerships that timely requested an automatic six-month extension, your 2025 calendar year return (Form 1065) is due. Alongside filing the return, ensure that you provide each partner with a copy of their Schedule K-1 (Form 1065) or a substitute Schedule K-1. Where applicable, remember to include Schedule K-3 (Form 1065) or a substitute Schedule K-3 (Form 1065).

September 15: Social Security, Medicare, and Withheld Income Tax

If you are an employer and the monthly deposit rules apply to your business, September 15 is your deadline to deposit Social Security, Medicare, and withheld income tax for the month of August 2026. This date also serves as the due date for the nonpayroll withholding deposit for August 2026, provided the monthly deposit rule applies.

September 30: Fiduciaries of Estates and Trusts

Fiduciaries handling estates and trusts face a late-month deadline. If you were given a 5½-month extension, you must file your 2025 calendar year return (Form 1041) by September 30. If applicable, you must also provide each beneficiary with a copy of their Schedule K-1 (Form 1041) or a substitute Schedule K-1.

Weekend and Holiday Rules

Filing deadlines offer slight flexibility when they fall on a weekend or holiday. If any due date lands on a Saturday, Sunday, or legal holiday, the deadline is automatically extended until the next business day that is not itself a legal holiday.

Disaster Area Extensions

Please note that when a geographical area is designated as a disaster area, due dates will be extended. To find out if a specific region has received a disaster declaration and to verify the extended filing dates, you can visit the following websites:

Stay Ahead of Your Fall Tax Deadlines

Managing these due dates helps ensure your business remains in good standing as we move into the final quarter of the year. If you have questions about your specific filing requirements, estimated payments, or extended returns, Michael Robertson and the team at Robertson Financial Group in Tucker, Georgia, are ready to assist. Contact our office today to schedule a tax planning consultation.

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