Missed a quarterly payment? Here's what actually happens

How the penalty actually works

The IRS underpayment-of-estimated-tax penalty isn't a single fee — it works like interest. For each quarterly period where you paid less than required, the IRS calculates a charge based on the shortfall amount and the number of days it remained unpaid, using the federal short-term rate plus 3 percentage points, adjusted quarterly. Details: IRS Topic 306 and the full calculation in Underpayment of Estimated Tax by Individuals.

Two things follow directly from that mechanism:

• Paying immediately stops further accrual on that specific shortfall — it doesn't erase what's already accrued for the days it sat unpaid, but it caps it.
• Payments apply to the earliest underpayment first. If you're behind on Q2 and it's now Q3, a payment credits to the older, longer-outstanding Q2 shortfall before anything newer — which reduces the total penalty more than letting it sit would.

What to actually do

1. Pay the missed amount now, through IRS Direct Pay or EFTPS — don't wait for the next quarterly date.
2. Keep paying the current quarter's amount on schedule too, so you're not compounding a second shortfall on top of the first.
3. File Form 2210 with your return if you want the IRS's own worksheet to calculate the exact penalty rather than letting the IRS calculate and bill it — useful if your income was uneven across the year (the "annualized income" method can lower the penalty for gig work with seasonal swings).

Ways the penalty can be reduced or waived

The IRS waives or reduces the penalty in specific situations: you didn't pay because of a casualty, disaster, or other unusual circumstance; you retired (after age 62) or became disabled during the tax year and the underpayment was due to reasonable cause; or your total underpayment for the year is under the safe-harbor thresholds (generally 90% of the current year's tax or 100% of last year's tax, 110% if last year's AGI was over $150,000). Full detail: Topic 306.

The four 2026 dates, for reference

See the full quarterly payment guide for how to calculate what you owe each period, including the 2026 split mileage rate for your deduction.