September 2025 business tax deadlines include S corporation and partnership filings with extensions, corporate estimated payments, and payroll tax deposits due September 15.
**September 15 - S Corporations
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File a 2024 calendar year income tax return (Form 1120-S) and pay any tax due. This due date applies only if you requested an automatic 6-month extension. Provide each shareholder with a copy of their Schedule K-1 (Form 1120-S) or a substitute Schedule K-1 and, if applicable, Schedule K-3 (Form 1120-S) or substitute Schedule K-3
September 15 - Corporations
Deposit the third installment of estimated income tax for 2025 for calendar year corporations.
September 15 - Partnerships
File a 2024 calendar year return (Form 1065). This due date applies only if you were given a 6-month extension. Provide each partner with a copy of their Schedule K-1 (Form 1065) or a substitute Schedule K-1 and, if applicable, Schedule K-3 (Form 1065) or 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, September 15 is the due date for you to make your deposit of Social Security, Medicare, and withheld income tax for August 2025. This is also the due date for the nonpayroll withholding deposit for August 2025 if the monthly deposit rule applies.
Weekends & Holidays:
If a due date falls on a Saturday, Sunday or legal holiday, the due date 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. For more information whether an area has been designated a disaster area and the filing extension dates visit the following websites:
FEMA: https://www.fema.gov/disaster/declarations
IRS: https://www.irs.gov/newsroom/tax-relief-in-disaster-situations
