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Key September 2025 Tax Deadlines for Businesses

September 2025 heralds crucial tax deadlines for businesses, particularly for those who've opted for extensions on S corporation and partnership filings. In addition, there are important due dates for corporate estimated tax payments and payroll tax responsibilities due by September 15.

September 15 - S Corporations

For S Corporations, it's time to file your 2024 calendar year income tax return using Form 1120-S and settle any outstanding taxes. This deadline applies if you received a 6-month extension. Every shareholder must receive their Schedule K-1 (Form 1120-S) or alternative forms like Schedule K-3, if applicable. This ensures transparency and compliance for all parties involved.

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September 15 - Corporations

Corporations are required to deposit their third installment of estimated income tax for the 2025 calendar year. Ensuring timely and accurate tax deposits is vital for maintaining the financial health and compliance of your business operations.

September 15 - Partnerships

If you're managing a partnership, your 2024 calendar year return (Form 1065) is due—given you were granted a 6-month extension. Each partner must also be provided with their respective Schedule K-1 (Form 1065) or a Schedule K-3 (Form 1065) substitute, if required. This is essential for accurate distribution of income and tax liability among partners.

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September 15 - Social Security, Medicare, and Withheld Income Tax

Employers must adhere to the monthly deposit rules for Social Security, Medicare, and withheld income tax payments for August 2025 by this date. Additionally, if nonpayroll withholdings are applicable, ensure these deposits are made on time to avoid penalties.

Weekends & Holidays

If a tax deadline falls on a weekend or legal holiday, it automatically extends to the next business day that isn't itself a legal holiday—offering a slight reprieve for those managing tight schedules.

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Disaster Area Extensions

In instances where a region is declared a disaster area, tax filing dates may be extended. For the latest updates on disaster designations and potential extensions, consult the following resources:

FEMA: https://www.fema.gov/disaster/declarations

IRS: https://www.irs.gov/newsroom/tax-relief-in-disaster-situations

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