The numbers
| Penalty | Rate | Cap |
|---|---|---|
| Failure to file | 4.5% of the tax owed, per month or part of a month | 5 months (22.5%) |
| Failure to pay | 0.5% of the unpaid tax, per month | Until paid |
| Interest | Federal short-term rate plus 3%, compounded daily | Until paid |
Example
An 80,000 lb truck owes $550 for the year. File it four months late and the IRS adds about $99 in failure-to-file penalty, $11 in failure-to-pay, and a few dollars of interest. Roughly $660 instead of $550. Not ruinous. The expensive part is the truck sitting without plates while you wait.
No stamped Schedule 1, no plates. State DMVs and IRP offices require proof that the HVUT was paid before they'll register or renew a truck. DOT officers ask for it at inspections too.
Filing late still helps
The failure-to-file penalty stops accruing the day the IRS receives your return. If you have a reasonable cause for filing late, you can attach an explanation; the IRS sometimes waives the penalty for a first offense with a clean history.