After 3 years unfiled and unpaid, $5,000 in back taxes grows to about $8,548. That includes $3,548 in total penalties and interest. The IRS adds failure-to-file and failure-to-pay penalties plus daily compounded interest.
The math
Inputs
| Tax owed | $5,000 |
|---|---|
| Return due | April 18, 2023 |
| Return filed | 36 months late (April 18, 2026) |
| Tax paid in full | 36 months after the due date (April 18, 2026) |
The formula in words
Failure-to-file: 5% of the unpaid tax for each month or part of a month the return is late, up to 5 months (25%). Failure-to-pay: 0.5% of the unpaid tax per month, up to 25%. In a month when both apply, the failure-to-file charge is reduced by the failure-to-pay charge, and the failure-to-pay charge stays the same. Both penalties are charged only on tax that is still unpaid. If the return is more than 60 days late, the failure-to-file penalty is at least $450 (returns due in 2023) or 100% of the tax, whichever is less. Interest: the IRS rate, compounded daily, on the tax and the failure-to-file penalty from the due date until you pay.
Step by step
| Month late | Failure-to-file | Failure-to-pay | Penalties so far |
|---|---|---|---|
| 1 | $225.00 | $25.00 | $250.00 |
| 2 | $225.00 | $25.00 | $500.00 |
| 3 | $225.00 | $25.00 | $750.00 |
| 4 | $225.00 | $25.00 | $1,000.00 |
| 5 | $225.00 | $25.00 | $1,250.00 |
| 6 | $0.00 | $25.00 | $1,275.00 |
| 7 | $0.00 | $25.00 | $1,300.00 |
| 8 | $0.00 | $25.00 | $1,325.00 |
| 9 | $0.00 | $25.00 | $1,350.00 |
| 10 | $0.00 | $25.00 | $1,375.00 |
| 11 | $0.00 | $25.00 | $1,400.00 |
| 12 | $0.00 | $25.00 | $1,425.00 |
| 13 | $0.00 | $25.00 | $1,450.00 |
| 14 | $0.00 | $25.00 | $1,475.00 |
| 15 | $0.00 | $25.00 | $1,500.00 |
| 16 | $0.00 | $25.00 | $1,525.00 |
| 17 | $0.00 | $25.00 | $1,550.00 |
| 18 | $0.00 | $25.00 | $1,575.00 |
| 19 | $0.00 | $25.00 | $1,600.00 |
| 20 | $0.00 | $25.00 | $1,625.00 |
| 21 | $0.00 | $25.00 | $1,650.00 |
| 22 | $0.00 | $25.00 | $1,675.00 |
| 23 | $0.00 | $25.00 | $1,700.00 |
| 24 | $0.00 | $25.00 | $1,725.00 |
| 25 | $0.00 | $25.00 | $1,750.00 |
| 26 | $0.00 | $25.00 | $1,775.00 |
| 27 | $0.00 | $25.00 | $1,800.00 |
| 28 | $0.00 | $25.00 | $1,825.00 |
| 29 | $0.00 | $25.00 | $1,850.00 |
| 30 | $0.00 | $25.00 | $1,875.00 |
| 31 | $0.00 | $25.00 | $1,900.00 |
| 32 | $0.00 | $25.00 | $1,925.00 |
| 33 | $0.00 | $25.00 | $1,950.00 |
| 34 | $0.00 | $25.00 | $1,975.00 |
| 35 | $0.00 | $25.00 | $2,000.00 |
| 36 | $0.00 | $25.00 | $2,025.00 |
| Charged on | Amount | Interest |
|---|---|---|
| Unpaid tax | $5,000 | $1,243.06 |
| Failure-to-file penalty | $1,125 | $279.69 |
Result
- Failure-to-file penalty: $1,125
- Failure-to-pay penalty: $900
- Interest: $1,523
- Total penalties and interest: $3,548
- Total to pay the IRS: $8,548
Assumptions
- Nothing was paid before April 18, 2026 and no extension was filed.
- IRS interest compounded daily at the individual underpayment rate (irs.gov quarterly interest rates): 7% from April 18, 2023; 8% from October 1, 2023; 7% from January 1, 2025; 6% from April 1, 2026.
- Interest on the failure-to-pay penalty is left out: it only starts once the IRS bills you for it, so the real total can be a little higher.
- No penalty relief assumed. First-time abatement or reasonable cause can remove penalties (not interest) if you qualify.
- These are estimates that show how the math works, not financial, tax or legal advice. Lenders, card issuers and the IRS can calculate slightly differently.
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What the $8,548 total means for you
If you owe $5,000 and do nothing for 3 years, the IRS doesn't just wait. The $5,000 grows to $8,548. That's $3,548 in total penalties and interest on top of the original tax. The biggest single piece is interest at $1,523, followed by the failure-to-file penalty at $1,125 and the failure-to-pay penalty at $900.
For a stressed reader, the key point is that the total is not a flat fee. It builds month by month. The failure-to-file penalty hits hardest early because it's 5% of the unpaid tax for each month or part of a month the return is late, up to 5 months. That's why it reaches $1,125. The failure-to-pay penalty is slower at 0.5% per month, but it keeps running for the full 36 months, reaching $900. Interest compounds daily on the tax and the failure-to-file penalty, so it grows even while you're deciding what to do.
This is an estimate that shows how the math works. The IRS can calculate slightly differently, and the real total can be a little higher because interest on the failure-to-pay penalty is left out here. It only starts once the IRS bills you for it. Confirm your exact balance with the IRS before you pay.
What drives the growth: penalties and interest
Three charges push $5,000 to $8,548. First, the failure-to-file penalty: 5% of the unpaid tax for each month or part of a month the return is late, up to 5 months. That caps at 25% of the unpaid tax, or $1,125 here. Second, the failure-to-pay penalty: 0.5% of the unpaid tax per month, up to 25%. Over 36 months, that's $900. Third, interest: the IRS rate, compounded daily, on the tax and the failure-to-file penalty from the due date until you pay. Using the rates in the assumptions, that's $1,523.
One detail matters: in a month when both penalties apply, the failure-to-file charge is reduced by the failure-to-pay charge, and the failure-to-pay charge stays the same. Both penalties are charged only on tax that is still unpaid. Because nothing was paid before April 18, 2026, the full $5,000 stayed unpaid the whole time, so the penalties ran on the full amount.
The failure-to-file penalty stops growing after 5 months, but the failure-to-pay penalty and interest keep going. That's why the total keeps climbing even after the first 5 months. If the return is more than 60 days late, the failure-to-file penalty is at least $450 or 100% of the tax, whichever is less — but here the 5% monthly calculation already produces $1,125, so that minimum doesn't change the result.
How you could change the outcome
The numbers above assume nothing was paid before April 18, 2026 and no extension was filed. Change either of those and the total changes. Paying earlier reduces the unpaid tax that penalties and interest are charged on. Filing earlier stops the failure-to-file penalty from reaching its 5-month cap. An extension moves the return due date, which can reduce or delay the failure-to-file penalty.
Penalty relief is another lever. No penalty relief is assumed here, but first-time abatement or reasonable cause can remove penalties — not interest — if you qualify. That could remove the failure-to-file and failure-to-pay penalties, leaving the $1,523 interest and the $5,000 tax. The exact relief depends on your situation, so confirm with the IRS.
Interest is harder to remove. It compounds daily at the IRS underpayment rate, and the assumptions use 7% from April 18, 2023; 8% from October 1, 2023; 7% from January 1, 2025; and 6% from April 1, 2026. Those rates are set quarterly, so the interest total depends on when you pay. The sooner you pay, the less interest accrues.
Practical next steps
If you're in this situation, don't wait for the number to grow. Here's what to do next:
- File your return. Even if you can't pay, filing stops the failure-to-file penalty from running further. It's already at its 5-month cap here, but filing is still the first step.
- Pay what you can. Any payment reduces the unpaid tax that penalties and interest are charged on. The failure-to-pay penalty and interest are charged only on tax that is still unpaid.
- Ask about penalty relief. First-time abatement or reasonable cause can remove penalties if you qualify. That doesn't remove interest, but it can cut the total.
- Set up a payment plan. If you can't pay in full, the IRS offers installment agreements. Confirm the terms with the IRS.
- Check your exact balance. These are estimates. The IRS can calculate slightly differently, and interest on the failure-to-pay penalty can add more once you're billed.
This is not financial, tax or legal advice. Lenders, card issuers and the IRS can calculate slightly differently. Confirm your specific numbers with the IRS or a tax professional before making decisions.
Frequently asked questions
What happens if I file but can't pay the full $5,000?
Filing stops the failure-to-file penalty from growing, but the failure-to-pay penalty and interest continue on the unpaid tax. Pay what you can to reduce the balance. You can ask the IRS about a payment plan. Confirm the terms with the IRS.
Can penalties be removed if I have a good reason for filing late?
Yes, first-time abatement or reasonable cause can remove penalties if you qualify. That could remove the failure-to-file and failure-to-pay penalties here, but not the $1,523 in interest. You need to request relief and confirm your eligibility with the IRS.
Does the failure-to-file penalty keep growing after 5 months?
No. The failure-to-file penalty is 5% of the unpaid tax per month, up to 5 months, so it caps at 25% or $1,125 here. The failure-to-pay penalty and interest keep running until the tax is paid.
How is interest calculated on back taxes?
Interest is the IRS rate, compounded daily, on the tax and the failure-to-file penalty from the due date until you pay. Rates change quarterly. In this example, interest totals $1,523 over 3 years. Confirm current rates with the IRS.
Will the IRS calculate the same $8,548 total?
Not necessarily. These are estimates. The IRS can calculate slightly differently, and the real total can be a little higher because interest on the failure-to-pay penalty is left out here. It only starts once the IRS bills you. Check your exact balance with the IRS.