IRS Forms / Pubs & Penalties

The Failure to File penalty is 5% of the unpaid taxes for each month or part of a month that a tax return is late. The penalty won't exceed 25% of your unpaid taxes.
If both a Failure to File and a Failure to Pay penalty are applied in the same month, the Failure to File penalty is reduced by the amount of the Failure to Pay penalty for that month, for a combined penalty of 5% for each month or part of a month that your return was late.
If after 5 months you still haven't paid, the Failure to File penalty will max out, but the Failure to Pay penalty continues until the tax is paid, up to its maximum of 25% of the unpaid tax as of the due date.
If the return is more than 60 days late, the minimum Failure to File penalty is the amount shown below or 100% of the underpayment, whichever is less:

Return Due Date (without extension) Minimum Amount

On or before 12/31/2008 $100.00

Between 01/01/2009 and 12/31/2015 $135.00

Between 01/01/2016 and 12/31/2017 $205.00

Between 01/01/2018 and 12/31/2019 $210.00

Between 01/01/2020 and 12/31/2022 $435.00

Between 01/01/2023 and 12/31/2023 $450.00

After 12/31/2023 $485.00