How the IRS Late Filing & Payment Penalty Calculator Works
The IRS charges two separate penalties when a tax return is late: the Failure-to-File penalty (5% of unpaid tax per month, capped at 25%) and the Failure-to-Pay penalty (0.5% of unpaid tax per month, also capped at 25%). If you filed on time but just paid late, only the Failure-to-Pay penalty applies. If you didn't file at all, both penalties apply — but the IRS doesn't simply add 5% + 0.5%. For any month where both penalties overlap, the Failure-to-File penalty is reduced by the Failure-to-Pay amount for that month, so the combined rate works out to 5% per month rather than 5.5%.
This calculator applies that offset automatically: enter your unpaid tax, how many months late you are, and whether you also filed the return late. It estimates each penalty separately and then totals them with the IRS's overlap rule already applied, so the number is closer to what a real notice would show than a naive percentage calculation.
Two things this tool simplifies: it does not add IRS interest (charged daily on top of the tax and penalties, at a rate that changes quarterly), and it does not apply the minimum penalty rule that kicks in when a return is filed more than 60 days late (a flat $510 or 100% of the unpaid tax, whichever is smaller, for 2024 returns). If you're in that situation, treat this estimate as a floor rather than the final number, and consider the IRS Fresh Start or an installment agreement to manage what you owe.
Frequently Asked Questions
Yes, if you didn't file at all. But when both penalties apply in the same month, the IRS reduces the 5% failure-to-file penalty by the 0.5% failure-to-pay penalty for that month, so the combined rate is capped at 5% per month rather than 5.5%.
Failure-to-file penalties cap at 25% of the unpaid tax, and failure-to-pay penalties also cap at 25%. If you file more than 60 days late, there's also a minimum penalty of $510 (2024) or 100% of the unpaid tax, whichever is smaller.