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If you’re self-employed, run a pass-through business, or earn income that isn’t subject to withholding, September 15 isn’t just another date on the calendar it’s your Q3 2026 estimated tax deadline. Miss it or underpay, and the IRS doesn’t wait until April to let you know; you’ll owe interest and penalties calculated from the date the payment was due.
Here’s a practical checklist to get your Q3 payment right, plus what to watch for as you head into Q4.
Estimated taxes apply to income the IRS doesn’t automatically withhold tax from. That typically includes:
As a general rule, if you expect to owe $1,000 or more in tax for the year after withholding and credits, you’re expected to make quarterly estimated payments.
Pull actual numbers from your books through the end of Q3 not a rough guess. If your business had a strong summer or a slow one, that changes what you owe now.
Many Houston business owners set their estimated payments in January based on last year’s numbers, then never revisit them. If revenue, expenses, or your entity structure changed mid-year, your Q3 payment should reflect that not the January projection.
You generally avoid an underpayment penalty if you’ve paid at least 90% of this year’s tax liability or 100% of last year’s liability (110% if last year’s adjusted gross income was over $150,000). Confirming you’re on track for one of these thresholds by Q3 gives you time to correct course before Q4.
Self-employment tax (Social Security and Medicare) is often the piece business owners underestimate. If you’re paying yourself as a sole proprietor or single-member LLC, this applies on top of regular income tax.
Sold a property, took a large distribution, had a one-time consulting payout, or exercised equity? Events like these can meaningfully change what you owe and are easy to forget by the time September rolls around.
Payments can be made through IRS Direct Pay, EFTPS, or by mail with Form 1040-ES. Electronic payment is faster to confirm and leaves a clear record — worth using if you’ve had payment issues in prior quarters.
Once Q3 is paid, take five minutes to estimate whether your Q4 payment (due January 15, 2027) will need adjusting based on how the rest of the year is trending.
The IRS calculates an underpayment penalty based on the shortfall and how long it went unpaid it isn’t a flat fee, and it accrues from the missed due date, not from when you eventually file your return. For business owners with fluctuating income, this is one of the more common and avoidable penalties, since it usually comes down to using a stale estimate rather than an inability to pay.
Unlike April’s tax deadline, Q3 estimated payments tend to get less attention there’s no single big filing event forcing a full review of the numbers. That’s exactly why business owners with growing or seasonal income are most likely to underpay here: last quarter’s number gets recycled without checking if it still fits.
The September 15 deadline is a good forcing function to check in on your business’s actual year-to-date performance, not just carry forward a number from January. A quick review now can prevent a penalty later and gives you a clearer picture heading into year-end tax planning.
September 15, 2026. Since that falls on a Tuesday, there’s no weekend extension — the payment is due that day.
You can make a larger payment now, but it won’t fully eliminate penalties for the earlier missed quarters, since underpayment penalties are calculated quarter by quarter. It’s still worth catching up as soon as possible to stop penalties from accruing further.
S-corp income passes through to the owner’s personal return via a K-1, so estimated payments are typically made personally, not by the business — separate from any payroll withholding on a W-2 salary you take from the S-corp.
You’re generally protected if your total withholding and estimated payments for the year equal at least 90% of this year’s tax bill or 100% of last year’s (110% for higher earners). Confirming this requires comparing your actual year-to-date numbers against last year’s return.
You’ll owe the full tax bill plus an underpayment penalty calculated on the amount and the length of time each quarter’s payment was late — even if you pay the full balance by the April filing deadline.
Schedule a consultation with Jasmine Saluja, CPA and we’ll confirm your numbers, check your safe harbor position, and make sure Q4 is set up correctly too.
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Jasmine Saluja, CPA is a Houston-based CPA firm providing expert bookkeeping, tax preparation, and proactive tax planning for medical practices, law firms, and home service businesses. We help clients stay organized, compliant, and financially confident.
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