IRS Penalty and Interest Calculator

5% of the unpaid tax for each month or part of a month the return is late, up to 25%. A return more than 60 days late has a minimum penalty: $525 for returns due in 2026, or the full tax owed if that is less.

0.5% of the unpaid tax for each month or part of a month, up to 25%. In months when both penalties apply, the late filing penalty is reduced by the late payment amount.

IRS interest is the federal short-term rate plus 3%, reset each quarter and compounded daily. It runs on unpaid tax from the original due date, and on some penalties, until the balance is paid.

An extension gives more time to file, usually until October 15, but not more time to pay. Tax not paid by the April due date still builds the late payment penalty and interest.

First-time penalty relief may apply with a clean history for the prior three years. Reasonable cause, such as a serious illness or a disaster, may also qualify. Interest is generally not removed.

The Franchise Tax Board has its own late filing and late payment penalties and interest, so an unfiled California return adds to the total shown here.