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September 2025: Essential Business Tax Deadlines

As we navigate through the fiscal obligations of September 2025, it's imperative for businesses to keep a close eye on key tax deadlines to ensure compliance and financial efficiency. This month, focus on your S corporation and partnership filings with extensions, corporate estimated payments, and required payroll tax deposits, all due by September 15.

Key Dates for September:

September 15 - S Corporations
By this date, S corporations are required to file their 2024 calendar year income tax return (Form 1120-S) and settle any owed taxes. This deadline affects entities that have secured a six-month extension. Ensure each shareholder is furnished with a copy of their Schedule K-1 (Form 1120-S) or an equivalent, and if relevant, Schedule K-3 (Form 1120-S) or its substitute.

September 15 - Corporations
Calendar year corporations must deposit their third installment of estimated income tax for 2025 on this date.

September 15 - Partnerships
Partnerships should file the 2024 calendar year return (Form 1065), applicable only if a six-month extension was granted. Distribute Schedule K-1 (Form 1065) or an equivalent to each partner, alongside Schedule K-3 (Form 1065) or its substitute if required.

September 15 - Social Security, Medicare, and Withheld Income Tax
If monthly deposit rules apply, this date marks the deadline for employers to remit deposits for Social Security, Medicare, and withheld income tax pertaining to August 2025. The same deadline applies for nonpayroll withholding deposits under the monthly rule.

Weekend & Holiday Adjustments:

In the event that a deadline falls on a weekend or official holiday, it is automatically extended to the next working day.

Disaster Area Extensions:
Special concessions apply for businesses located in federally designated disaster zones, granting extensions on filing dates. Confirm your area's status and new deadlines via the following resources:
FEMA Disaster Declarations
IRS Tax Relief in Disaster Scenarios

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