What should I know about IRS penalties and interest?

Interest

Generally, interest accrues on any unpaid tax from the due date of the return until the date of payment in full. The interest rate is determined quarterly and is the federal short-term rate plus 3 percent. Interest compounds daily. You can find the current quarterly interest rate on underpayments by
visiting the IRS Newsroom.

Penalties

In addition, if you file a return but don't pay all tax owed on time, you'll generally have to pay a late payment penalty. The failure-to-pay penalty is one-half of one percent for each month, or part of a month, up to a maximum of 25%, of the amount of tax that remains unpaid from the original due date of the return (without extension) until the tax is paid in full. The one-half of one percent rate increases to one percent if the tax remains unpaid 10 days after the IRS issues a notice of intent to levy property. If you file your return by its due date and request an installment agreement, the one-half of one percent rate decreases to one-quarter of one percent for any month in which an installment agreement is in effect. Be aware that the IRS applies payments to the tax first, then any penalty, then to interest. Any penalty amount that appears on your bill is generally the total amount of the penalty up to the date of the notice, not the penalty amount charged each month.

If you owe tax and don't file on time, there's also a penalty for not filing on time. The failure-to-file penalty is usually five percent of the tax owed for each month, or part of a month that your return is late, up to a maximum of 25%. If your return is over 60 days late, there's also a minimum penalty for late filing; it's the lesser of $435 (for tax returns required to be filed in 2020) or 100 percent of the tax owed.