Learning Center

Essential September 2025 Tax Deadlines for Businesses

As businesses navigate the fiscal landscape, staying on top of tax deadlines is key to maintaining compliance and avoiding penalties. In September 2025, there are several pivotal tax obligations for business entities, including S corporations, partnerships, and employers. Understanding these deadlines can support strategic planning and ensure smooth operations. Below, we detail the critical dates and requirements.

Image 1

September 15 - S Corporations
For S corporations, the due date for filing a 2024 calendar year income tax return (Form 1120-S) arrives on September 15 if an automatic 6-month extension has been issued. Additionally, it is the responsibility of the corporation to deliver each shareholder a Schedule K-1 (Form 1120-S) or a suitable substitute, along with the Schedule K-3, if applicable. Ensure these documents are accurately prepared to avoid compliance issues.

September 15 - Corporations
Corporations must also remember to deposit the third installment of estimated income tax for 2025 by September 15. This payment is essential for calendar year corporations, supporting efficient tax management and cash flow planning.

Image 2

September 15 - Partnerships
Partnerships, too, face the same deadline for filing a 2024 calendar year return (Form 1065) if they have a 6-month extension. As with S corporations, partners must receive their respective Schedule K-1 (Form 1065) or substitutes, alongside the potential Schedule K-3.

Let’s Talk!
Get Expert Help Now
Book With Us

September 15 - Social Security, Medicare, and Withheld Income Tax
Employers who follow the monthly deposit rule for Social Security, Medicare, and withheld income taxes must make their deposits by September 15 for August 2025. This date also applies to nonpayroll withholding deposits.

Image 3

Weekends & Holidays:
Should any tax due date fall on a Saturday, Sunday, or legal holiday, the deadline extends to the next business day that is not a holiday. This extension allows additional preparation time when circumstances necessitate it.

Disaster Area Extensions:
It's crucial to be informed about potential disaster area declarations, which provide additional time for tax filings. The IRS and FEMA websites offer ongoing updates on areas granted disaster relief extensions. Check the following websites for the latest information and extended filing deadlines: FEMA and IRS.

Let’s Talk!
Get Expert Help Now
Book With Us
Share this article...

Sign up for our newsletter.

Each month, we will send you a roundup of our latest blog content covering the tax and accounting tips & insights you need to know.

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 .

We care about the protection of your data.

Social Media

Taxx Guy LLC

129 Underhill Lane
Peekskill, New York 10566