You may owe past-due taxes for several reasons, including:
• Submitting a return but failing to pay the full balance owed
• Leaving out part of your income on a tax return
• Not filing a tax return at all
These situations can be deliberate, like purposely understating income, or accidental, such as not having enough tax withheld throughout the year.

To avoid additional fines for not filing, we always recommend filing on time even if payment isn’t possible right away, rather than skipping the return altogether.
Below are the two main penalties and what they typically cost:
Failure to File: Interest owed plus a 5% penalty per month the return is late, up to 25% of the total bill. The IRS might even file a substitute return for you, which won’t include deductions or credits that could lower your balance.
Failure to Pay: Interest owed, plus a 0.5% monthly late fee.
Depending on your case, the IRS could take harsh collection actions, such as seizing wages, placing a lien on your property, or other enforcement measures.