Estimated Tax Payment Dates 2026: September Deadline and Late-Payment Rules

Information checked: 2026-09-09 · Maintenance label: Annual fixed window

The third quarterly instalment of estimated tax is due September 15, covering income earned from 1 June through 31 August.

If you are self-employed, have significant investment income, or receive income without withholding, this is the deadline that arrives with the least warning, because nothing arrives in the post to remind you.

This guide covers the four payment periods, who has to pay, the safe harbour rules that protect you from a penalty, and what happens when a payment is late.

Key takeaway

The four due dates are April 15, June 15, September 15 and January 15 of the following year. You generally must pay estimated tax if you expect to owe $1,000 or more when you file. Paying at least 90% of the current year's tax or 100% of last year's tax, whichever is smaller, generally avoids the underpayment penalty.

Table of contents

• The four payment periods
• Who has to pay
• The safe harbours
• What happens if a payment is late
• A practical routine
• Frequently asked questions
• Summary

Related guides

• 2026 Tax Extension Deadline: What to File and Pay Before October 15 — If you also filed an extension and still owe tax

The four payment periods

Payment	Income earned	Due
First	1 January to 31 March	15 April
Second	1 April to 31 May	15 June
Third	1 June to 31 August	15 September
Fourth	1 September to 31 December	15 January of the following year

Note that the periods are not equal quarters. The third covers three months and the second covers two, which is a common source of miscalculation.

If a due date falls on a Saturday, Sunday or legal holiday, the IRS treats a payment as on time if it is made on the next day that is not one of those.

Pay directly, without a fee to a middlemanIRS payment options ›Direct Pay, card and payment plan options in one place. Paying something before the deadline reduces the penalty even if you cannot pay in full.

Who has to pay

Individuals generally have to make estimated tax payments if they expect to owe $1,000 or more in tax when the return is filed, after subtracting withholding and credits. For corporations the threshold is $500.

The people most often caught out are those whose situation changed during the year:

• Started freelancing or contracting alongside or instead of employment
• Sold an asset and realised a capital gain
• Began receiving rental income
• Took a retirement distribution without adequate withholding
• Had a significantly higher income year than the last one

The safe harbours

You generally avoid the underpayment penalty if any of these is true:

• You owe less than $1,000 in tax after subtracting withholding and credits
• You paid at least 90% of the tax for the current year
• You paid 100% of the tax shown on the prior year's return

The IRS applies whichever of the 90% and 100% figures is smaller. Higher-income taxpayers are subject to a different threshold, so check Form 1040-ES or Publication 505 if your income is substantially above the prior year.

The prior-year safe harbour is the practical one for anyone with unpredictable income. You do not have to forecast this year accurately; you have to cover last year's number.

What happens if a payment is late

The underpayment penalty is not a flat fine. It is calculated per period, on the amount underpaid, for the days it remained unpaid. Two consequences follow.

First, a late payment is better than a skipped one, because the penalty stops accruing on the amount once it is paid. Second, and less obviously, the IRS warns that you may be charged a penalty even if you are due a refund when you file, because the penalty is assessed on the periods you underpaid rather than on the year's final balance.

If your income arrived unevenly during the year, the annualised income instalment method on Form 2210 may reduce or eliminate the penalty. That is worth investigating if a single large payment in one quarter is producing a penalty across all of them.

A practical routine

1. Find last year's total tax figure on your prior return.
2. Divide it by four. That is your default per-period payment under the prior-year safe harbour.
3. Pay it on each of the four dates, through an IRS payment option rather than a third-party service.
4. If income rises sharply, increase the later payments rather than waiting until filing.
5. If you also have employment income, increasing withholding is an alternative, since withholding is treated as paid evenly through the year.

That last point is a genuinely useful lever. A withholding increase late in the year can repair earlier underpayment in a way that a late estimated payment cannot.

Frequently asked questions

What if I miss the September deadline?

Pay as soon as you can. The penalty accrues on the underpaid amount for the period it stays unpaid, so paying late is materially better than waiting until filing.

Are the four periods equal quarters?

No. The third period covers 1 June to 31 August, three months, while the second covers only 1 April to 31 May.

Can I avoid estimated tax by increasing withholding?

Often yes. Withholding is generally treated as paid evenly across the year, which is why it can repair an earlier shortfall.

Do I still owe a penalty if I get a refund?

Possibly. The IRS states you may be charged a penalty even if you are due a refund, because the penalty is assessed on the periods you underpaid.

What is the safest target if my income is unpredictable?

The prior-year safe harbour, since it uses a number you already know rather than a forecast. Higher-income taxpayers face a different threshold, so check Form 1040-ES.

Summary

September 15 covers June through August. Miss it and the penalty runs on that amount until you pay, so pay late rather than not at all.

For unpredictable income, cover last year's tax rather than forecasting this year's. It is the safe harbour built from a number you already have.