Essential Tax Deadlines for Businesses: September 2025

As we transition into September 2025, important business tax deadlines require the attention of all diligent enterprises. Key dates this month include final extensions for S corporation and partnership filings, corporate estimated payments, and crucial payroll tax deposits, all due by September 15. Staying informed ensures compliance and assists in strategic financial planning.

September 15 - Key Filing for S Corporations
Businesses operating as S corporations must finalize their 2024 calendar year income tax return, utilizing Form 1120-S, and settle any outstanding taxes. Ensure each shareholder receives their respective Schedule K-1 (Form 1120-S), along with applicable Schedule K-3. Compliance hinges on these details, especially for entities that availed of a 6-month filing extension.

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September 15 - Corporate Estimated Income Tax
Calendar year corporations need to deposit the third installment for estimated income tax for 2025 by this date. This deadline is pivotal in managing quarterly financial obligations and ensuring cash flow aligns with tax liabilities.

September 15 - Crucial Returns for Partnerships
Partnership entities must finalize and file their 2024 calendar year return using Form 1065. If you’ve been granted a 6-month extension, ensure each partner receives their Schedule K-1 and, where applicable, Schedule K-3, maintaining transparency and tax compliance.

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September 15 - Social Security, Medicare, and Withheld Income Tax
Employers under monthly deposit rules must submit their August 2025 deposit for Social Security, Medicare, and withheld income tax by September 15. Nonpayroll withholdings are also due under similar regulations. Adherence to these dates avoids penalties and supports payroll accuracy.

Considering Weekends and Holidays
When tax due dates fall on a weekend or legal holiday, they are automatically deferred to the subsequent business day. This flexibility aids in maintaining deadlines without compromising compliance.

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Understanding Disaster Area Extensions
Designations of disaster areas can further extend filing deadlines. Stay updated through resources from FEMA and IRS for specific extensions available.

These September deadlines signal essential responsibilities for businesses striving to comply with tax obligations while optimizing their financial strategies. At Melvin P. Crilley, EA Inc., our commitment to personalized, proactive support helps navigate these complexities with ease.

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