Key Tax Deadlines for September 2025: Stay Compliant

September 2025 marks an important month for businesses with several tax obligations on the horizon. Ensuring timely compliance can help avoid unnecessary penalties and interest, allowing you to focus on strategic growth and planning.

September 15 - S Corporations

For S Corporations operating on a calendar year, this is the due date to file your 2024 income tax return (Form 1120-S) if you've secured a 6-month extension. It's also crucial to provide each shareholder with their Schedule K-1 or substitute forms, and if applicable, Schedule K-3.

September 15 - Corporations

Calendar year corporations must deposit their third installment of 2025 estimated income tax by this date, ensuring continued alignment with IRS requirements.

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September 15 - Partnerships

Similar to S Corporations, if you've opted for a 6-month extension, now is the time to file your 2024 return (Form 1065). Distribute the necessary Schedule K-1 and, where applicable, Schedule K-3 forms to partners.

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

Employers adhering to monthly deposit rules must ensure deposits for August 2025’s Social Security, Medicare, and withheld income tax are completed by this date. This deadline also applies to the nonpayroll withholding for August, under similar rules.

Considerations for Weekends and Holidays

Whenever these deadlines fall on weekends or federal holidays, they automatically extend to the next business day, ensuring you have adequate time to meet your obligations.

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Disaster Area Extensions

Should a natural disaster affect your area, special extensions might be available. Always check with FEMA or IRS updates to confirm your eligibility for such provisions.

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