Essential September 2025 Tax Deadlines for Businesses

As September 2025 approaches, it's crucial for businesses, especially small business owners, to prepare for key tax deadlines. From compliance with S corporation and partnership filings to estimated payments and payroll obligations, understanding these dates is essential for maintaining financial health and compliance. Here's a detailed guide to help you navigate this important month.

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September 15 - S Corporations

For S corporations, September 15 is the deadline to file a 2024 calendar year income tax return (Form 1120-S), provided you filed for a 6-month extension earlier this year. It's also the time to distribute copies of each shareholder's Schedule K-1 or, if applicable, Schedule K-3. Timely filing ensures your business remains compliant and avoids any late penalties.

September 15 - Corporations

This date also marks the third installment due for estimated income tax payments for calendar year corporations. Ensuring these payments are made can prevent underpayment penalties, ensuring smoother operations for your business.

September 15 - Partnerships

Partnerships must file their 2024 calendar year return (Form 1065) if they obtained a 6-month extension. Just like S corporations, partners should receive their Schedule K-1 or Schedule K-3 documents by this date.

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

Employers adhering to monthly deposit rules need to make their deposits for Social Security, Medicare, and withheld income tax for August 2025 by this deadline. This also applies to nonpayroll withholding deposits if you follow the monthly deposit schedule.

Weekends & Holidays:

It’s important to note that if any of these dates fall on a weekend or a public holiday, your due date extends to the next business day. This built-in flexibility allows for efficient planning and execution of tax duties.

Disaster Area Extensions:

Businesses operating in a designated disaster area may be eligible for extended deadlines. Stay informed about these potential extensions by visiting the FEMA website at https://www.fema.gov/disaster/declarations and the IRS at https://www.irs.gov/newsroom/tax-relief-in-disaster-situations.

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Staying on top of these deadlines with the guidance of Tax Time 365, your trusted virtual firm, will ensure a seamless compliance experience for your business. Our expertise in providing tailored tax services for small business owners across the United States is here to support you every step of the way.

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