Estimated tax penalty calculator (Form 2210, 2026)

How the penalty is figured

This follows Part III of Form 2210, the regular method, and its Penalty Worksheet. The required annual payment is split into four equal installments, one per due date. Withholding is treated as paid in four equal parts on those dates unless you can show when it was actually withheld. Every other payment is applied to the earliest installment that still has a balance, so a late June payment first fills whatever April left open.

For each piece of an installment paid late, the penalty is the amount times the number of days late divided by 365, times the IRS underpayment rate for individuals in effect during those days. Days run from the day after the due date through the day the payment arrives, and stop on April 15 of the following year, when the return is due. Form 2210 lays the year out in four rate periods: April 16 to June 30, July 1 to September 30, October 1 to December 31, and January 1 to April 15, with the January period running at the first-quarter rate the whole way.

The rates used here come from the IRS quarterly interest rate table and IR-2026-98: 7% in every quarter of 2025, then 7% for the first quarter of 2026, 6% for the second and 7% for the third and fourth. The IRS announces each quarter's rate a few weeks before it starts, so the rate for January 1 to April 15, 2027 is not yet published. Days in that period are priced at the last known 7% and labelled as an estimate; the IRS sets the rate at the federal short-term rate plus 3 percentage points, so a one-point move changes the result by about 14%.

The "pay the rest on" box answers the question people actually have in October: what does it cost to settle today versus in January? It takes every installment still open after your entered payments, treats it as paid on that date, and adds the result to what has already accrued. Paying earlier always costs less; the days already counted do not go away.

What this does not model

Form 2210 Schedule AI, the annualized income installment method, is not included. If most of your income arrived late in the year, Schedule AI can shrink the earlier installments and the penalty with them, and it has to be filed with your return. The short method on Form 2210 is a simplification of the same math for people who paid on the due dates or not at all; it gives nearly the same answer as the regular method used here, and the IRS applies the regular method when any payment was late.

Also left out: the exceptions that remove the penalty entirely (no tax liability last year as a full-year U.S. citizen or resident, tax minus withholding under $1,000, farmers and fishermen), the waiver for casualty, disaster, retirement or disability, the married filing separately $75,000 threshold for the 110% rule, estates and trusts, and any state penalty. The IRS figures this penalty itself if you leave Form 2210 off your return, so the number here is for deciding when to pay, not a substitute for the form. The safe-harbor rules behind the required annual payment are worked through in estimated tax safe harbor, and the estimated tax calculator gives you the required amount from your profit.