Learning Center
We keep you up to date on the latest tax changes and news in the industry.

Important Business Tax Deadlines: September 2025

The month of September 2025 is a crucial period for managing business tax responsibilities effectively. Key deadlines include filings for S corporations and partnerships with prior extensions, as well as corporate estimated tax payments and payroll obligations, all due by September 15.

September 15 - S Corporations
File your 2024 tax return (Form 1120-S) if you obtained a 6-month extension, along with any owed taxes. Ensure shareholders receive their Schedule K-1 (Form 1120-S) or substitute versions, including, if necessary, Schedule K-3 (Form 1120-S).

Image 1

September 15 - Corporations
Corporations on a calendar year should deposit their third installment of estimated income tax for 2025 by this date.

September 15 - Partnerships
Submit your 2024 return (Form 1065) if a 6-month extension was granted. Each partner must receive their respective Schedule K-1 (Form 1065) or substitute, along with Schedule K-3 (Form 1065), if applicable.

Call Today
We solve tax problems for individuals and help tax pros solve tax problems for their clients.
Contact Us

Image 2

September 15 - Social Security, Medicare, and Withheld Income Tax
Employers following monthly deposit rules must remit Social Security, Medicare, and withheld taxes for August 2025 by this deadline. The same applies to nonpayroll withholdings if subject to monthly deposits.

Weekends & Holidays
Should a deadline coincide with a weekend or legal holiday, the due date moves to the next business day that is not a holiday.

Disaster Area Extensions
In designated disaster areas, extensions are permissible. Stay informed through FEMA and IRS resources, which provide details on declared disaster areas and adjusted filing deadlines.

Call Today
We solve tax problems for individuals and help tax pros solve tax problems for their clients.
Contact Us
Share this article...

Want tax & accounting tips and insights?

Sign up for our newsletter.

I confirm this is a service inquiry and not an advertising message or solicitation. By clicking “Submit”, I acknowledge and agree to the creation of an account and to the and .
IRS Tax Pros Ask Us A Question
Welcome To IRS Tax Pros Ai - Your smart assistant.
Please fill out the form and our team will get back to you shortly The form was sent successfully