If you take income that is not run through payroll — distributions, self-employment income, rental income, a K-1, a big capital gain — the IRS expects you to pay tax on it as you earn it, not in April. The third instalment for 2026 is due Tuesday, September 15. It is the payment most business owners get wrong, because the “third quarter” is not the third quarter.
Key Takeaways
- The third estimated tax payment for 2026 is due September 15, 2026.
- It covers income earned June 1 through August 31 — the “quarters” are not equal three-month blocks.
- You are generally required to pay if you expect to owe $1,000 or more after withholding and credits.
- The safe harbor is the number that matters: 90% of this year’s tax, or 100% of last year’s — 110% if your 2025 AGI was over $150,000.
- The underpayment rate is 7% for the third and fourth quarters of 2026, charged as interest from each missed due date.
What the September 15 payment actually covers
Estimated tax periods are not calendar quarters, and this trips up owners who try to reason from the name. For the 2026 tax year the four periods run like this:
- April 15, 2026 — income earned January 1 to March 31 (three months)
- June 15, 2026 — income earned April 1 to May 31 (two months)
- September 15, 2026 — income earned June 1 to August 31 (three months)
- January 15, 2027 — income earned September 1 to December 31 (four months)
All four 2026 due dates fall on weekdays, so there is no weekend or holiday shift to lean on this year. If your summer was your strong season — and for a lot of DFW contractors, restaurants and event businesses it is — the September payment is the big one, because it is carrying three months of your best revenue.
Who actually has to make it
The general rule is simple: if you expect to owe $1,000 or more in tax when you file, after subtracting your withholding and refundable credits, you are required to make estimated payments. That catches:
- Sole proprietors and single-member LLC owners
- Partners and multi-member LLC members receiving a K-1
- S-corporation shareholders, on the distribution side of their income
- Anyone with meaningful 1099, rental, interest, dividend or capital-gain income
It also catches people who do have a W-2 but whose withholding no longer covers a growing side business. A spouse’s paycheque withholding is a legitimate way to cover the household’s liability — but only if someone has actually done the arithmetic.
The safe harbor is the number that matters
Here is the part worth internalising: you do not have to predict this year’s tax perfectly. You only have to clear one of three bars. Pay at least the smallest of:
- 90% of your total 2026 tax, or
- 100% of the total tax shown on your 2025 return, or
- 110% of your 2025 tax if your 2025 adjusted gross income was more than $150,000
… and the underpayment penalty does not apply, however well or badly the year actually turns out.
For a business having a strong year, the prior-year safe harbor is usually the cheaper and far easier target. Take last year’s total tax, multiply by 100% or 110%, divide by four, and pay that. You will settle the difference in April. For a business having a weak year, the 90%-of-current-year route is better, because it lets you pay less now rather than overfunding the IRS on the strength of a better prior year.
Our 2026 estimated tax calculator works both routes, and the full estimated tax guide walks through the calculation in more detail.
What missing it actually costs
The underpayment charge is not a flat fine. It is interest, calculated per period, running from each missed due date until the money is paid. The rate for individuals is the federal short-term rate plus three percentage points, reset quarterly. For 2026 that rate is 7% for the first, third and fourth quarters, and 6% for the second.
Two consequences follow from “it is interest, not a fine”:
- Paying late is better than not paying. The meter stops the day the payment lands, so a September 20 payment costs five days of interest, not a quarter’s worth.
- It is not deductible. Unlike genuine business interest, this is a personal tax charge and does nothing for your return.
The withholding lever most owners do not know about
This is the single most useful thing in this article if you are already behind.
Tax withheld from wages is treated as though it was paid evenly across the whole year, no matter when in the year it was actually withheld. Estimated payments, by contrast, are credited on the date you make them. That asymmetry is a genuine planning tool.
If you missed the April and June instalments, a fourth-quarter estimated payment will not undo the interest that has already accrued on those periods. But if you or your spouse draw a W-2 — including an S-corporation owner drawing reasonable salary from your own company — increasing withholding for the rest of the year, or running a year-end bonus with heavy withholding, can be applied backwards across all four periods. In the right circumstances it cures earlier underpayments outright.
This is worth a conversation before December, not after. If you are an S-corp shareholder, it also interacts with how you set salary in the first place — see LLC vs S-corp in Texas.
How to pay it
Three routes, all fine:
- IRS Direct Pay — free, straight from a bank account, no enrolment. Fastest option for an individual paying at the last minute. Select “Estimated Tax” and tax year 2026.
- EFTPS — free, but enrolment takes several days because a PIN arrives by mail. Corporations paying their own estimated tax must use it, so enrol before you need it.
- Form 1040-ES voucher by mail — still valid. Postmark by September 15.
Whichever route you use, save the confirmation. Reconciling estimated payments at filing time is a common source of avoidable notices, and the IRS transcript is not always quick to reflect a recent payment.
If you are already behind on Q1 or Q2
Do not skip September to “sort it all out in January.” That is the most expensive version of this. Instead:
- Pay the September instalment on time, at the correct amount.
- Add a catch-up amount for the periods you missed, and pay it now rather than in January — every week of delay is more interest.
- Look at the withholding lever above, which is the only mechanism that reaches backwards.
- If cash is the real constraint, that is a different conversation — and a more urgent one. Our tax resolution page covers the options once a balance is already owed.
The Texas angle
Texas has no personal state income tax, so there is no state equivalent of the September 15 payment for individuals. That is genuinely good news, and it is part of why the federal instalment catches people out — there is no second reminder arriving from Austin.
What Texas does want from you sits on a different calendar entirely: the franchise tax report due May 15, and sales tax returns due the 20th of the month following each reporting period. Neither of those has anything to do with estimated income tax, and neither one covers you if you skip it.
A fifteen-minute check before September 15
- Pull your 2025 return and find total tax — the line for total tax, not the balance due or the refund.
- Was your 2025 AGI over $150,000? If yes, your prior-year target is 110% of that total tax; if no, 100%.
- Divide by four. That is your per-instalment safe-harbor number.
- Add up what you have actually paid in for 2026 so far, including any withholding.
- Pay the shortfall, plus this quarter’s instalment, by September 15.
If your income this year looks nothing like last year — you sold something, took on a large contract, or lost one — the shortcut stops being a shortcut and the arithmetic is worth doing properly.
Not sure what to send the IRS on September 15?
We will work out your safe-harbor number from your last return, tell you exactly what to pay, and set up the rest of the year so this stops being a scramble.
SCHEDULE MY FREE CALLOr call +1-214-807-2440
Frequently Asked Questions
When is the Q3 2026 estimated tax payment due?
The third estimated tax instalment for the 2026 tax year is due September 15, 2026. All four of the 2026 due dates fall on weekdays, so no weekend or holiday extension applies. The remaining dates for the year are April 15, 2026, June 15, 2026, September 15, 2026, and January 15, 2027 for the final instalment.
What income does the September 15 payment cover?
It covers income earned from June 1 through August 31, 2026. Estimated tax periods are not equal calendar quarters: the first covers three months, the second covers only April and May, the third covers June through August, and the fourth covers four months from September through December. Businesses with a strong summer often find the September instalment is their largest of the year.
How much do I have to pay to avoid a penalty?
You avoid the underpayment penalty by paying the smallest of 90 percent of your total 2026 tax, 100 percent of the total tax shown on your 2025 return, or 110 percent of your 2025 tax if your 2025 adjusted gross income was over 150,000 dollars. This is the safe harbor, and clearing it protects you regardless of how the year actually turns out.
What is the penalty for missing an estimated tax payment?
It is charged as interest rather than a flat fine, calculated separately for each period from the date the payment was due until it is paid. The rate is the federal short-term rate plus three percentage points, reset quarterly. For 2026 the underpayment rate is 7 percent for the first, third and fourth quarters and 6 percent for the second. Because it accrues daily, paying late still costs less than not paying.
Can I catch up on missed quarters later in the year?
Partly. An estimated payment is credited on the date you actually make it, so a later payment does not undo interest already accrued on an earlier period. Tax withheld from wages, however, is treated as paid evenly across the entire year no matter when it was withheld. Increasing payroll withholding or running a year-end bonus with heavy withholding can therefore reach backwards and cure earlier underpayments in a way an estimated payment cannot.
Do I owe Texas estimated tax payments too?
No. Texas has no personal state income tax, so there is no state counterpart to the September 15 instalment for individuals. Texas business obligations sit on separate calendars: the franchise tax report is due May 15 annually, and sales tax returns are due the 20th of the month following each reporting period.
Sources: Internal Revenue Service, Estimated Taxes and Form 1040-ES (2026 due dates, the $1,000 threshold, and the 90/100/110 percent safe harbor), retrieved 2026-08-29, irs.gov; Internal Revenue Service, Underpayment of Estimated Tax by Individuals Penalty and quarterly interest rate announcements for 2026, retrieved 2026-08-29, irs.gov; Texas Comptroller of Public Accounts, Sales and Use Tax and Franchise Tax filing calendars, retrieved 2026-08-29, comptroller.texas.gov. This article is general information, not individualized tax advice.