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Key September 2025 Tax Deadlines for Businesses

Tracking tax deadlines is crucial for businesses to avoid penalties and interest. September 2025 holds significant due dates for S corporations, partnerships, and more. Whether you're managing tax actions for your team or service clients, staying updated with these deadlines is essential. Image 2

September 15 - S Corporations
File your 2024 calendar year income tax return (Form 1120-S) and pay any taxes owed. This applies only if you’ve requested a 6-month extension. Ensure each shareholder receives their Schedule K-1 or a substitute, and if needed, Schedule K-3.

September 15 - Calendar Year Corporations
Corporations should deposit the third installment of estimated income tax for 2025. This is a critical task to fulfill corporate tax responsibilities efficiently.

September 15 - Partnerships
Submit your 2024 Form 1065 if a 6-month extension was granted. Partners should receive their Schedule K-1 or an equivalent document, as well as, if applicable, a Schedule K-3.

Social Security, Medicare, and Withheld Income Tax
If monthly deposit rules apply, ensure you submit your deposits for Social Security, Medicare, and withheld income taxes for August 2025 by September 15. Also, this date marks the deadline for nonpayroll withholding deposits, if applicable. Image 1

Adjustments for Weekends and Holidays
If any deadline lands on a weekend or legal holiday, it automatically extends to the next business day.

Consideration for Disaster Areas
In disaster-designated zones, tax filing and payment deadlines are extended. Visit FEMA and IRS for current information on such extensions. Keeping abreast of these changes can prevent missed deadlines and associated penalties.

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