Essential September 2025 Tax Deadlines for Businesses

Stay ahead of your business tax obligations with these critical deadlines for September 2025. This month, ensure that your S corporation, partnership filings, corporate estimated payments, and payroll tax deposits are all in compliance. Image 1

September 15 - S Corporation Requirements
File your 2024 calendar year income tax return (Form 1120-S) and pay any tax due if you opted for a 6-month filing extension. Ensure each shareholder receives their Schedule K-1 (Form 1120-S) or equivalent, and if applicable, include Schedule K-3 (Form 1120-S). This guarantees transparency and accurate reporting of income, deductions, credits, etc., for your shareholders.Image 2

September 15 - Corporate Estimated Payments
Calendar year corporations must deposit the third installment of estimated income tax for 2025 by this date. Accurate estimations help prevent underpayment penalties, safeguarding your business's financial health.

September 15 - Partnership Obligations
If your partnership received a 6-month extension, file the 2024 calendar year return (Form 1065). Distribute Schedule K-1 (Form 1065) or a substitute to all partners, and include Schedule K-3 (Form 1065) if necessary, ensuring partners can accurately file their tax returns.

September 15 - Payroll Tax Deposits
Employers following the monthly deposit rule must deposit Social Security, Medicare, and withheld income tax for August 2025 on this date. This includes any nonpayroll withholding obligations, maintaining compliance with federal tax mandates.Image 3

Considerations for Weekends & Holidays
When a deadline falls on a weekend or holiday, it extends to the next business day. Keep this in mind to avoid last-minute filing rushes and to maintain compliance.

Extensions for Disaster Areas
Regions designated as disaster areas receive deadline extensions for filing. To check if your area qualifies and for extension dates, explore resources from FEMA at FEMA Disaster Declarations and the IRS at IRS Disaster Tax Relief.

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