Essential September 2025 Tax Deadlines for Businesses

As September 2025 approaches, it's crucial for businesses to stay ahead of key tax deadlines. This month, S corporations and partnerships with extensions, corporate estimated payments, and payroll tax deposits are due on September 15. Maintaining compliance with these requirements can help businesses avoid unnecessary penalties and interest charges.

September 15 - S Corporations
For S corporations operating on a calendar year, this is the deadline to file your 2024 income tax return (Form 1120-S) and pay any due taxes. This applies only if an automatic 6-month extension was requested. Ensure that each shareholder receives their Schedule K-1 (Form 1120-S) and, if applicable, Schedule K-3 or their substitute forms.

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September 15 - Corporations
This is also the date for calendar year corporations to deposit the third installment of their estimated income tax for 2025. Maintaining timely payments throughout the fiscal year can help financial planning and cash flow management.

September 15 - Partnerships
If you were granted a 6-month extension, make sure to file your 2024 calendar year return (Form 1065) by this date. Disseminate Schedule K-1 (Form 1065) and, if necessary, Schedule K-3 or their substitute versions to each partner by the due date.

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September 15 - Social Security, Medicare, and Withheld Income Tax
Employers must deposit Social Security, Medicare, and withheld income tax payments for August 2025 by this date if they follow the monthly deposit rules. Similarly, any nonpayroll withholding for August must be deposited by this due date.

Weekends & Holidays:
Note that if any due date falls on a Saturday, Sunday, or legal holiday, it automatically extends to the next business day.

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Disaster Area Extensions:
In regions recognized as disaster areas, the IRS and other agencies may extend filing deadlines. For specific information about disaster declarations and extensions, please visit:

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