IRS Penalty Calculator

Missing a tax deadline triggers two separate charges plus interest, and seeing the combined figure in advance makes the cost of delay concrete. For tax year 2026, this estimate covers both the failure-to-file and failure-to-pay penalties along with the interest the IRS layers on top. The breakdown shows where each dollar comes from so you can weigh your options before the bill grows.

The failure-to-file penalty runs 5% of the unpaid tax for every month or partial month a return is late, stopping once it reaches 25%; if a return arrives more than 60 days late, a floor of $485 applies for 2026. Running alongside it, the failure-to-pay penalty adds 0.5% of the unpaid tax per month or partial month until the balance is cleared, also capped at 25%. On top of both penalties and the original tax, interest accrues, and for Q1 2026 the underpayment rate is 8% per annum, compounded daily.

An extension buys time to file but not time to pay, so the balance is still owed by the original deadline if you want to sidestep the failure-to-pay charge. Sending in as much as you can manage by that date, even a partial amount, shrinks both the penalties and the interest that build on the remainder. Two surprises catch filers off guard: interest compounds faster than expected, and penalties can still apply to a late return even when a refund is owed.