By the FL Innovation News editorial team · Business Development
By Sindy Ramos · Savvy Numbers
Every September, a few clients call me on the 14th in a mild panic: “Wait — is there a tax payment due tomorrow?” There is. The third-quarter estimated tax payment is due September 15, and it catches more Florida business owners off guard than any other deadline on the calendar, because it lands in the busiest, most distracted stretch of the year.
So here is the calm version. If you are self-employed, a partner, or an S-corp owner, this is everything you need to get it right in the next few days — without the panic.
Who actually has to pay
The rule is simpler than it sounds. According to the IRS, individuals — including sole proprietors, partners, and S corporation shareholders — generally have to make estimated payments if they expect to owe $1,000 or more when they file. Corporations hit the threshold at $500.
In plain English: if you have income that nobody is withholding tax from — client payments, 1099 work, partnership distributions, rental income — you almost certainly need to be paying quarterly. And here is the piece people forget: for self-employed owners that includes self-employment tax (Social Security and Medicare, about 15.3%), not just income tax.
How much to send: the safe-harbor math
You do not have to nail the exact number. You just have to pay enough to land inside the IRS “safe harbor,” which protects you from the underpayment penalty even if you owe more in April. Here is how to pick your target:
| Your situation | Safest target for the year |
|---|---|
| Income about the same as last year | Pay 100% of last year’s total tax, split across the four payments |
| Last year’s AGI was over $150,000 | Pay 110% of last year’s tax to be safe |
| Income dropped this year | Pay 90% of what you will actually owe this year (requires a real estimate) |
| Income spiked this year | The prior-year safe harbor still protects you from penalty — but set the extra aside now so April is not a shock |
The prior-year method is the one I recommend for most owners, because it is a known number: take the total tax from your 2025 return, divide by four, and you are done. That is the whole point of having a simple tax plan — the September payment stops being a guess.
The three-minute way to pay
- IRS Direct Pay (bank transfer, no fee) or EFTPS if you pay regularly. Choose “Estimated Tax” and tax year 2026.
- Florida bonus: there is no state income tax, so there is no state estimated payment to make. One deadline, not two.
- Save the confirmation. Screenshot it and drop it in your tax folder. You will want it in April.
What if you missed Q1 or Q2?
Do not skip Q3 to “even it out” — that makes it worse. Pay what you can now. The underpayment penalty is calculated like interest on the shortfall for each period, so every dollar you send earlier stops the meter on that dollar. If your income is lumpy (a big Q4, a slow spring), ask your bookkeeper about the annualized income method, which lets you pay based on when you actually earned the money.
The mistakes I see every September
- Forgetting self-employment tax. Owners estimate income tax and forget the 15.3% on top. It is usually the bigger surprise.
- Not adjusting after a great quarter. If summer was your best stretch ever, last year’s number will not cover it. The safe harbor protects you from penalty — not from the April bill.
- S-corp owners assuming payroll covers it. Your salary withholding covers your salary. Distributions and pass-through profit are what estimated payments are for.
- Guessing without books. If your bookkeeping is three months behind, you cannot estimate anything. Clean books are the tax plan.
Frequently asked questions
When exactly is the Q3 2026 estimated tax payment due?
September 15, 2026. The remaining payment for the year is due January 15, 2027. The IRS estimated-tax page lists the full schedule and payment methods.
What happens if I pay late or pay too little?
You may owe an underpayment penalty, which works like interest on the amount you should have paid for that period. It is rarely catastrophic, but it is entirely avoidable by hitting the safe harbor.
Do I have to make Florida state estimated payments?
No. Florida has no personal income tax, so sole proprietors, partners, and S-corp owners only make federal estimated payments.
Can I just pay more in January to catch up?
You can, and it helps, but the penalty is figured period by period, so a late catch-up does not fully erase the shortfall from earlier quarters. Paying on time each quarter is always cheaper.
The bottom line
September 15 is not a crisis — it is a number you already know if your books are current. Pick your safe-harbor target, send it through Direct Pay, and save the receipt. If you would rather never think about this deadline again, that is exactly the kind of thing we take off your plate; let’s talk.
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