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Tax Debt Calculator
By Priya Raman, Contributing Writer, Policy & RegulationEstimate your total IRS tax debt including failure-to-pay and failure-to-file penalties plus interest over time.
By Priya Raman, Contributing Writer, Policy & RegulationEstimate your total IRS tax debt including failure-to-pay and failure-to-file penalties plus interest over time.
Educational estimate combining IRS-style penalties and interest with your original balance.
Your original balance plus three additions: the failure-to-pay penalty, the failure-to-file penalty if you skipped filing, and interest that runs the whole time the balance sits unpaid.
Because the failure-to-file penalty runs about ten times faster than the failure-to-pay penalty. Filing a return you cannot pay in full is almost always cheaper than not filing at all.
It's close. This calculator uses roughly 8% a year as a simplified stand-in; the IRS resets the actual rate every quarter, and it was 7% for individuals in the third quarter of 2026.
Treat it as an estimate. The IRS computes the official figure, accounting for partial months, rate changes, and any payments you've already made.
Start with an $18,000 balance, ten months past due, return filed on time. The failure-to-pay penalty adds $900 (0.5% a month for ten months). Interest at roughly 8% a year adds about $1,200. Total owed: $20,100. Now imagine the return itself was never filed. The failure-to-file penalty adds $4,500 on top of the same failure-to-pay and interest charges, pushing the total to $24,600, roughly $4,500 more for the identical balance and timeline. That gap exists because the failure-to-file rate runs ten times faster than failure-to-pay, and it is the single biggest lever in this calculator.
The calculator applies the failure-to-pay penalty (0.5% a month, capped at 25%), the much larger failure-to-file penalty (5% a month) if you did not file, and interest (about 8% a year) to your original balance, then adds all three to the balance for the total.
None of these three charges are optional once a balance is late. Interest applies even to a balance that is only a few days overdue, and both penalties are calculated on the unpaid amount at the start of each month, not on the original tax bill, so a balance that is partly paid down will accrue less in later months than in earlier ones. If you eventually pay in full, the penalties and interest stop the day the balance hits zero.
| Charge | Rate | Source |
|---|---|---|
| Failure-to-pay penalty | 0.5% per month, capped at 25% | IRS.gov |
| Failure-to-file penalty | 5% per month, capped at 25% | IRS.gov |
| Underpayment interest, individuals (Q3 2026) | 7% per year, compounds daily | IRS.gov |
This calculator rounds interest to about 8% a year for simplicity; see the 2026 rates and thresholds reference for the exact current quarterly figure.