Critical September 2025 Tax Deadlines for Businesses

As a seasoned practitioner in tax strategy and financial management, it's imperative to be well-acquainted with the key tax dates in September 2025 that demand your attention. These deadlines are pivotal for S corporations, partnerships, and employers managing payroll taxes. Let’s delve into each to ensure compliance and strategic planning.

September 15 - S Corporations
If your S corporation operates on a calendar year, the deadline for filing the 2024 income tax return (Form 1120-S) arrives on September 15, provided an automatic 6-month extension was previously secured. On this date, all taxes due must be settled. Additionally, shareholders should receive their Schedule K-1 (Form 1120-S) or an equivalent, and if relevant, a Schedule K-3.

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September 15 - Corporations
Corporate entities must ensure the deposit of the third installment of their estimated income tax for 2025. Compliance here is crucial for managing cash flow efficiently and avoiding IRS penalties.

September 15 - Partnerships
For partnerships that have obtained a 6-month extension, your deadline also falls on September 15 for filing the 2024 calendar year return (Form 1065). Partners are to receive their Schedule K-1 or substitute accordingly, with applicable Schedule K-3 documents.

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September 15 - Social Security, Medicare, and Withheld Income Tax
Employers guided by monthly deposit rules must make their contributions for Social Security, Medicare, and withheld income tax by September 15, covering August 2025. Adherence is critical to maintaining compliance and financial prudence.

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Weekends & Holidays:
If any due date falls on a weekend or recognized national holiday, it rolls over to the subsequent business day.

Disaster Area Extensions:
In instances where your geographical location is declared a disaster area, extensions may apply. It is advisable to stay updated via official platforms like FEMA and the IRS for pertinent adjustments to filing dates.

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