September isn’t just back-to-school season—it’s also one of the busiest months for taxes. For both Minnesota individuals and businesses, September 15, 2025, is a date you don’t want to miss. Multiple deadlines converge on this day, and overlooking even one could mean penalties, interest, or unnecessary stress.
Here’s your quick guide to the September 15th tax deadlines—and what they mean for you.
1. Individuals: Q3 2025 Estimated Tax Payment Due
If you’re self-employed, a freelancer, or anyone whose income isn’t fully covered by withholding, the IRS expects you to pay taxes throughout the year. That means making quarterly estimated tax payments.
- Deadline: September 15, 2025
- Form to Use: Form 1040-ES
- What It Covers: Your third installment of 2025 federal estimated taxes
Why It Matters: Missing an installment doesn’t just add up in April—it can trigger IRS penalties for underpayment. Think of this payment as keeping you “even” with the IRS, so tax season isn’t a shock.
2. Businesses: Estimated Tax Payments
C-Corporations
- Deadline: September 15, 2025
- What’s Due: Third-quarter estimated tax payment
C-corporations are required to make estimated tax payments throughout the year, and Q3 is due now.
S-Corporations & Partnerships (Electing PTE)
- Deadline: September 15, 2025
- What’s Due: Q3 2025 Pass-Through Entity (PTE) tax, if your business elected into Minnesota’s PTE regime
Why It Matters: PTE elections can help offset federal SALT deduction limits, but only if you stay current. Missing this payment could jeopardize your election benefits.
3. Businesses: Extended Returns Due
If your S-Corporation or Partnership runs on a calendar year and you filed a six-month extension back in March, this is the final deadline.
- Deadline: September 15, 2025
- What’s Due: 2024 extended business tax return filing (Form 1120-S or Form 1065)
Why It Matters: The extension buys time to file, but not to pay. If you owe taxes, they should have been paid earlier in the year. Missing this filing deadline can mean steep late-filing penalties, even if the tax itself was already paid.
Why These Deadlines Sneak Up
Here’s what makes September 15 tricky:
- It’s not a “traditional” tax season date, so it’s easy to forget.
- Multiple deadlines overlap—for individuals and different types of businesses.
- Many small business owners are juggling back-to-school, Q3 operations, and cash flow crunches at the same time.
That’s why so many end up caught off guard.
The Bottom Line
For Minnesota individuals and businesses, September 15th isn’t just another day—it’s a tax deadline triple threat. Whether it’s estimated taxes, PTE payments, or extended returns, missing the date creates headaches that could have been avoided.
Our advice: don’t treat September 15 like just another Monday. Put it on your calendar, double-check your records, and make sure every return and payment is in order.
And if juggling estimated payments, PTE elections, and return deadlines feels like too much? That’s exactly where having a one-stop team behind you makes all the difference. We help Minnesota taxpayers stay on top of every deadline—so you can focus on running your life or business, not watching the calendar.