Failure to pay tax owed by the due date can result in a penalty. The deadline to file and pay your federal income tax is usually April 15. However, the due date for 2020 was extended to May 17, 2021.
If you are unable to make payment by the due date the IRS will assess a penalty of 0.5% for each month the tax is outstanding with a maximum penalty of 25%.
There are certain circumstances, such as for reasonable cause, where the late payment penalty can be removed.