September 15th Tax Deadline: Who Needs to File and What You Should Do Now - MABE International Advisors

Sep 02 2025 13:00

If youre a U.S. business owner, freelancer, or investor with pass-through income, September 15th is one of the most important tax deadlines of the year. Missing it could mean penalties, interest charges, and unnecessary stress.

So who exactly needs to mark this date on their calendar? Lets break it down.

Who the September 15th Deadline Applies To

The September 15th tax return deadline generally applies to:

  • Partnerships (Form 1065)  If you filed for an extension back in March, your partnership tax return is due by September 15th.
  • S Corporations (Form 1120-S)  Extended returns for S corporations are also due on this date.
  • Estimated Taxes for Q3  Individuals, freelancers, and business owners who make estimated quarterly payments must pay their third installment by September 15th.
  • Trusts & Estates (certain cases)  Some fiduciary returns with extensions also fall under this deadline.

In short: if you filed an extension for your partnership or S corp return, or if you owe Q3 estimated taxes, September 15th is your day of reckoning.

Why It Matters

Failing to meet the September 15th deadline can trigger:

  • Late filing penalties (up to $210 per month, per partner/shareholder).
  • Interest charges on unpaid tax balances.
  • Loss of credibility with investors or lenders if your filings are consistently late.

Its not just about compliance its about protecting your business reputation and cash flow.

What To Do Before September 15th

  1. Gather Your Documents
    Collect all income statements, expense reports, and financial records your CPA will need.
  2. Confirm Extensions
    Double-check that you (or your tax professional) filed an extension back in March. If not, your return was technically due months ago, and penalties may already apply.
  3. Submit Your Return
    Work with your tax preparer to file electronically before the deadline. The IRS considers e-filed returns received on time if submitted before midnight.
  4. Make Estimated Payments
    If you owe Q3 estimated taxes, pay them online via IRS Direct Pay or EFTPS to avoid interest.
  5. Plan Ahead
    Use this deadline as a reminder to review your tax planning for 2024. Proper planning now can reduce stress (and taxes owed) next year.

Takeaway

September 15th isnt just another date its the line between staying compliant and facing costly penalties.
If youre unsure whether this deadline applies to you, talk to your tax professional immediately.

 Need help with tax deadlines or compliance for your business? Contact our team today to make sure you never miss a date again.