Missing a quarterly tax payment

The penalty is interest, not a fine. It runs at 7% a year as of the fourth quarter of 2026, compounded daily, on whatever you were short. irs.gov

That framing matters more than it sounds, because people imagine a flat charge for being late and then either panic or ignore it. Neither is right. It is a meter, and it starts the day the payment was due.

How the charge is built

Two things surprise people.

It is calculated per period, not on the year. Each of the four windows is assessed separately against what you should have paid by that date. Paying nothing in April and everything in January does not net out — the April shortfall accrues from 15 April, regardless of what happens later. irs.gov

The rate moves. It is set as the federal short-term rate plus three percentage points and reset every quarter. irs.gov It was 6% in the second quarter of 2026 and 7% through 2025, so a figure you read in an article written last year is probably not the rate you will pay.

Interest compounds daily, which sounds severe and mostly is not, because the balances are small and the periods are short.

What it actually costs

It is worth knowing the size, because the fear of the penalty causes worse decisions than the penalty does. People drain a business account in a bad quarter to make a payment they could have deferred for a cost they never calculated.

When it is worth paying late on purpose

Rarely, but not never. If the alternative is card debt at a rate well above the IRS one, or missing payroll, then the underpayment interest irs.gov is the cheaper money — and treating the IRS as the most urgent creditor in the room is a reflex rather than a calculation.

Two conditions before that becomes reasonable: you actually have the money later, and you have run the number rather than guessed it. “I will catch up next quarter” without a figure attached is how a small interest charge becomes a large one.

Avoiding it entirely

Meet any one of the safe harbor tests and no underpayment charge applies at all, whatever you end up owing. irs.gov The most useful is paying 100% of last year’s total tax across four instalments — a number you already know exactly, requiring no forecast of a year that has not finished.

The safe harbor explained covers the three tests and when each applies.

If your income arrived unevenly, the charge may be reducible even after the fact: the annualized method recalculates each period against what you had actually earned by that date, which often removes the early-period shortfall entirely.

If you already missed one

Pay it now rather than at the deadline. Interest accrues daily, so the meter stops when the money arrives, not when the quarter ends. There is no benefit to waiting for the next scheduled date.

Do not skip the remaining payments. Being behind on one period does not excuse the next, and each is assessed on its own.

Let the IRS compute it. The default is that they calculate any charge and bill you, which is usually correct and costs no effort. File Form 2210 yourself only if you are claiming the annualized method or an exception.

Check whether you are actually short. Withholding from a W-2 job — yours or a spouse’s — counts toward the safe harbor and is treated as paid evenly across the year regardless of when it happened. A household with one salaried earner is often covered without realising it.

Where this stops applying

State penalties are separate, computed by each state on its own rules and its own rate. State estimated taxes covers the shape of that.

And this is the ordinary underpayment charge, not the penalties for failing to file or for failing to pay a balance shown on a return. Those are different, larger, and worth avoiding with more urgency than this one.