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Key September 2025 Tax Deadlines for Businesses

As we approach September 2025, businesses face crucial tax deadlines that require careful attention to maintain compliance and avoid penalties. In this post, we’ll detail the specific due dates for S corporations, partnerships, corporate estimated tax payments, and payroll tax deposits.

September 15 - S Corporations
For S corporations, the deadline to file a 2024 calendar year income tax return (Form 1120-S) and settle any tax obligations is September 15, 2025. This is only applicable if you opted for an automatic 6-month extension earlier this year. Ensure each shareholder receives their Schedule K-1 (Form 1120-S), and if necessary, Schedule K-3 (Form 1120-S) or their substitutes.

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September 15 - Corporations
Calendar year corporations must deposit the third installment of their estimated income tax for 2025 by this date. Proper planning and accurate calculation are essential to meet your tax liability obligations effectively.

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September 15 - Partnerships
Partnerships need to ensure their 2024 calendar year return (Form 1065) is filed by September 15 if they’ve utilized a 6-month extension. Distribute copies of Schedule K-1 (Form 1065) and, when applicable, Schedule K-3 (Form 1065), or their substitutes, to all partners.

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September 15 - Social Security, Medicare, and Withheld Income Tax
Employers adhering to monthly deposit rules must deposit their Social Security, Medicare, and withheld income tax for August 2025 by September 15. This also applies to nonpayroll withholding if the monthly rule is in effect.

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Weekends & Holidays
Remember, if any due date is on a weekend or legal holiday, it extends to the next business day. This simple adjustment can help keep your filings timely.

Disaster Area Extensions
For businesses in areas declared as disaster zones, deadlines are generally extended. Visit FEMA at FEMA Disaster Declarations or check the IRS’ site under Tax Relief in Disaster Situations for details on regional extensions.

Staying vigilant and informed about tax deadlines is crucial to business success. This planning ensures you remain compliant, avoid penalties, and can focus on thriving in your industry.

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