Q3 estimated taxes are due Tuesday, September 15, 2026. If you are self-employed, drive for a platform, freelance, or run anything that pays you without withholding tax, this is the one on the calendar right now.
It is also the deadline people miss most often, and there is a structural reason for that which almost nobody explains.
The "Quarters" Are Not Quarters
The IRS calls these quarterly payments, and everyone reasonably assumes they cover three months each. They do not. Here are the actual 2026 periods:
| Payment | Income earned | Length | Due |
|---|---|---|---|
| Q1 | Jan 1 – Mar 31 | 3 months | Apr 15, 2026 |
| Q2 | Apr 1 – May 31 | 2 months | Jun 15, 2026 |
| Q3 | Jun 1 – Aug 31 | 3 months | Sep 15, 2026 |
| Q4 | Sep 1 – Dec 31 | 4 months | Jan 15, 2027 |
Why this catches people: if you paid Q2 in June based on two months of income and then set aside "the same again" for September, you are short. Q3 covers fifty percent more time than Q2 did — and for most drivers and gig workers it also covers the busiest part of summer.
What You Actually Owe
Your September payment covers two separate taxes on the same profit:
- Self-employment tax — 15.3% (Social Security and Medicare), charged on 92.35% of your net profit. This one surprises people because an employer would normally pay half of it. Working for yourself, you pay both halves.
- Income tax — your ordinary rate, applied to the same profit after deductions.
The rough working figure most people use is 25–30% of net profit set aside as you earn. Our full guide to setting money aside works through the bracket maths properly.
The word doing the heavy lifting in both bullets is profit — not what the platform paid you. Everything you legitimately deduct comes off before either tax is calculated, which is where the next section matters.
Mileage Reduces This Payment, Not Next April's Refund
This is the part worth internalising if you drive at all for work. Business miles reduce net profit, and net profit is what both taxes above are computed on. So mileage does not just show up as a bigger refund in April — it lowers the cheque you write in September.
2026 has two rates, because the IRS raised it mid-year:
- 72.5¢ per mile for miles driven January 1 – June 30
- 76¢ per mile for miles driven July 1 – December 31
The Q3 window (June 1 – August 31) straddles that change: June is at 72.5¢, July and August at 76¢. A driver who logged 3,000 business miles across those three months is looking at roughly $2,270 off taxable profit — which, at a combined 25–30%, is around $570–$680 less to pay on September 15.
Miles you did not record are worth nothing. There is no retroactive way to prove a trip you never logged, and reconstructing a summer of driving from memory is exactly the kind of estimate that does not survive scrutiny. See what an audit-proof log actually needs.
Every mile you missed this summer was money
TaxMiles detects drives automatically, splits business from personal with one swipe, and applies the correct IRS rate for the date of each trip — including the mid-year change. Your deduction total is ready when the deadline is.
Download TaxMiles FreeThe Safe Harbor: How to Stop Worrying About Getting It Exact
You do not have to predict your year perfectly. The IRS provides a floor — hit it, and no underpayment penalty applies no matter what you owe at filing:
- 90% of your total 2026 tax, or
- 100% of your total 2025 tax — rising to 110% if your 2025 adjusted gross income was over $150,000
The second option is the practical one, because it is a number you already have. Take last year's total tax, divide by four, pay that each quarter, and you are protected regardless of how this year turns out. If 2026 is a much better year, you will owe a balance in April — but no penalty on top of it.
If you are having a much worse year than last: the prior-year safe harbor may be more than you need to pay. In that case the 90%-of-current-year route is cheaper, and it is worth running the numbers rather than overpaying a quarter you cannot easily get back before April.
Missed It? Pay Anyway
There is no flat late fee for a missed estimated payment. The charge is an underpayment penalty calculated like interest — it accrues on the amount you were short, for the time you were short.
Two consequences follow, and both are good news:
- Late is better than never. Paying on September 20 costs a fraction of paying on January 15.
- Partial is better than nothing. The penalty is proportional to the shortfall, so sending what you can genuinely reduces it.
The worst option is the common one: skipping the payment entirely because you cannot cover the full amount, then compounding it in the next quarter.
How to Actually Pay
- IRS Direct Pay — free, straight from a bank account, no registration. The simplest route for most people.
- EFTPS — free, but enrolment takes several days by post, so it is not an option if you are reading this in September.
- Debit or credit card — instant, but a processing fee applies. Fine if it saves you missing the date.
Whichever you use, make sure the payment is applied to 2026 estimated tax and not to a prior-year balance. Misapplied payments are tedious to unpick.
Set Yourself Up for January
The Q4 payment is due January 15, 2027, and it covers four months — September through December — making it the largest of the year for most people. It also lands immediately after the holidays.
The habit that fixes this permanently is separating the money as it arrives rather than finding it at the deadline: a second account, a fixed percentage moved on every payout, and a mileage log that runs itself. Do that and quarterly deadlines stop being events.
Related reading: how much to set aside for taxes, deductions every self-employed worker should know, the mid-year mileage rate change, and the rideshare driver tax guide.
This article is general tax education, not tax advice. Rules described are for federal taxes in the United States; state estimated-tax deadlines and rules may differ. Consult a tax professional about your specific situation.