September 2025 tax and compliance deadlines

What’s up in September? For many tax pros, you’ll get back to business after a busy summer with family and friends. For others, important extension filings are just around the corner and you’re getting ready for those. Along the way, check out these important tax and compliance deadlines for September 2025, and be sure to share this list with your clients.

In September, it is recommended that you:

• Finalize extended returns: Complete S Corporation and partnership returns before the September 15 deadline
• Confirm estimated tax payments: Notify clients about the 3rd estimated tax payment and confirm submission. 
• Conduct year-end tax planning: Identify tax-saving strategies for high-net-worth individuals and business clients. 
• Join a new professional group or mastermind: Find a group that focuses on tax strategy, business growth, or even something unrelated to tax.

Key Compliance Dates

Wednesday, September 10—Tips reporting for August.

Friday, September 12—Regular method excise taxes deposit for the last 16 days of August.

Monday, September 15:

• 3rd installment of 2025 estimated tax (individuals and corporations).
• S Corporation (1120-S) and Partnership (1065) returns due (if extended).
• Monthly payroll tax deposit for August (Form 941).

Thursday, September 25—Communications and air transportation taxes deposit for the last 16 days of August.

Monday, September 29— Regular method excise taxes deposit for the first 15 days of September.

Tuesday, September 30:

• Wagering tax (Form 730) and Heavy Highway Vehicle Use Tax (Form 2290) for August due. 
• Final due date for special September deposit rules (excise tax).

Intuit® Accountant Resources

• The September 2025 calendar with filing deadlines and reminders for you and your clients.
• One Big Beautiful Bill summary and tax changes
• Navigating the tax landscape
• Intuit Tax Guide 2024
• IRS annual inflation adjustments for tax years 2024 and 2025
• Key Tax Facts for 2024 and Key Tax Facts for 2025