Are you a business owner who makes quarterly estimated tax payments? August is the perfect time to check if you’re paying the right amount. Waiting until December or next April could cost you in penalties or missed opportunities—so a quick review now can help you avoid unpleasant surprises when you file.

Why check your quarterly tax payments now?

We’re into the 3rd quarter, which means you’ve got solid year-to-date numbers and still time to correct course before year-end. Many business owners wait too long to adjust withholding or estimated payments, and that’s when penalties or cash-flow problems show up.

Important deadlines to know (calendar-year taxpayers)

Estimated tax payments are generally due April 15, June 15, September 15, and January 15 of the following year. If a due date falls on a weekend or holiday, it’s moved to the next business day. For 2025 the upcoming calendar dates you should care about are September 15, 2025 (Q3) and January 15, 2026 (Q4).

Pro tip about 2025 June dates: in 2025 some June deadlines are observed on June 16, 2025 because June 15 falls on a weekend—so always confirm the observed date if you’re looking back at what you already paid.

How to check if you’re paying the right amount

1. Pull your profit & loss for January through July 2025 and compare it to the projections you used to set your estimated payments.
2. Are you ahead or behind your original plan? If you’re earning more, consider increasing the September payment to avoid underpayment penalties; if you’re earning less, you may be able to reduce upcoming payments and free up cash.
3. Compare what you’ve already paid (April, June—or their observed dates) to your updated annual estimate. Use Form 1040-ES or your tax software to run a fresh estimate.
   

Safe-harbor rules — avoid underpayment penalties

You can avoid an underpayment penalty by paying either:

• 90% of the current year’s tax liability, OR
• 100% of last year’s tax liability (substitute 110% if your prior-year AGI was more than $150,000, or $75,000 if married filing separately).

These are standard IRS safe-harbor thresholds; use them to test whether you’re protected.

Special cases & state rules

Some taxpayers (farmers/fishermen or fiscal-year filers) have special rules or different due dates, and state estimated-tax rules and deadlines can vary. If you fall into any of these categories, check IRS Publication 505 and your state tax agency guidance or ask your tax advisor.

What to do next (action checklist)

1. Gather your YTD numbers (January–July 2025).
2. Recalculate your year-end tax estimate (use Form 1040-ES or tax software).
3. Talk with your tax advisor about whether to change the September 15, 2025 payment.
4. Mark September 15, 2025 and January 15, 2026 on your calendar (and check for any observed date shifts).
   

Need help?

Fat Wallet Tax specializes in making sure business owners pay the right amount each quarter—so you don’t overpay or face penalties. Schedule a Cash Flow Confidence Call now for a quick 3rd-quarter tax check-up and keep your cash flow healthy.