# What is my IRS late payment penalty?

Works out the IRS failure-to-pay penalty (0.5% a month, up to 25%) and the interest on unpaid tax at the IRS quarterly rates, compounded daily, from the due date to the day you pay.

- Page: https://www.acalculator.org/finance/irs-late-payment-penalty-calculator
- JSON spec: https://www.acalculator.org/finance/irs-late-payment-penalty-calculator.json
- Version: 2faa31a37ede

## Default answer

Example with the default inputs (Unpaid tax $5,000.00, Payment due date April 15, 2026, Date you pay September 30, 2026, I have an installment agreement No) on the example date Wednesday, September 30, 2026: Paying $5,000.00 of tax on September 30, 2026 instead of April 15, 2026 costs $150.00 in penalty and $152.82 in interest.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| tax | Unpaid tax | The tax shown on your return that was not paid by the due date. |
| due | Payment due date | The date the tax was due, usually April 15 (the next business day when it falls on a weekend or holiday). |
| paid | Date you pay | The date you pay the tax in full. |
| plan | I have an installment agreement | Whether an IRS installment agreement cuts the penalty to 0.25% a month (return filed on time). |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| total | Penalty and interest | The failure-to-pay penalty plus the interest on the unpaid tax. |
| penalty | Failure-to-pay penalty | 0.5% (0.25% with an installment agreement) of the unpaid tax for each month or part of a month, at most 25%. |
| interest | Interest | Interest on the unpaid tax at the IRS underpayment rate, compounded daily. |
| unpaid | Unpaid tax | The unpaid tax, as typed. |
| amountDue | Total to pay | The unpaid tax plus the penalty and the interest. |
| months | Months late | Months or parts of a month from the due date to the payment date. |
| days | Days late | Days from the due date to the payment date. |
| penaltyRate | Penalty as a share of the tax | The penalty as a percent of the unpaid tax (25% at most). |

## Method

Penalty = unpaid tax × 0.5% (0.25% with an installment agreement) × months or parts of a month late, at most 25% of the tax. Interest = tax × (Π over each day from the due date to the day before payment of (1 + rate ÷ days in the year)) − tax, with the IRS underpayment rate for that day’s quarter.

## Assumptions

- An estimate, not tax advice. The IRS figures the exact amounts on its notice.
- The return was filed on time: the failure-to-file penalty (5% a month) is not included, and neither is the higher 1% rate after an IRS notice of intent to levy.
- The tax is paid in one amount on the payment date; no partial payments, credits, or first-time penalty relief.
- Interest is on the unpaid tax only. The IRS also charges interest on the penalty from its notice date, which is not included.
- A month runs from the due date to the same day of the next month (the last day of a shorter month); from a due date on a month’s last day, to the last day of the next month (IRM 20.1.2.3.8.4.2).
- Interest rates cover January 1, 2018 to December 31, 2026 (IRS quarterly rates).

## Worked examples

1. tax = $10,000.00, due = 2025-04-15, paid = 2025-10-15, plan = no gives months = 6, penalty = $300.00, interest = $357.16, total = $657.16. Source: IRC 6651(a)(2): 6 × 0.5% × 10,000; interest at 7% (IRS quarterly rates, 2025) compounded daily over 183 days.
2. tax = $5,000.00, due = 2024-04-15, paid = 2026-09-29, plan = no gives months = 30, penalty = $750.00, interest = $965.24.
3. tax = $2,000.00, due = 2020-07-15, paid = 2025-07-15, plan = no gives months = 60, penalty = $500.00, penaltyRate = 25%, interest = $643.41. Source: IRC 6651(a)(2): the penalty stops at 25% (60 months would be 30%).
4. tax = $8,000.00, due = 2025-04-15, paid = 2026-04-16, plan = yes gives months = 13, penalty = $260.00, interest = $578.13. Source: IRC 6651(h): 0.25% a month under an installment agreement.

## FAQ

### How much is the IRS penalty for paying late?

The failure-to-pay penalty is 0.5% of the unpaid tax for each month or part of a month it stays unpaid, up to 25% of the tax (IRC 6651(a)(2)). With an IRS installment agreement on a return filed on time, it drops to 0.25% a month (IRC 6651(h)).

### How does IRS interest on unpaid tax work?

Interest runs from the due date until you pay, at the federal short-term rate plus 3 percentage points, set each quarter. It is compounded daily. For individuals the rate was 7% for most of 2025 and 2026.

### Is the penalty the same as interest?

No. The penalty is a fixed share of the tax per month; interest grows day by day with the quarterly rate. The IRS charges both, and interest cannot be waived for reasonable cause, while the penalty sometimes can.

### What about filing late?

The failure-to-file penalty is separate and larger: 5% of the unpaid tax a month, up to 25%. When both apply in a month, the filing penalty is reduced by the payment penalty. This calculator assumes you filed on time (or had an extension).

### Can the penalty be removed?

The IRS offers first-time penalty relief if you had no penalties in the past three years, and relief for reasonable cause such as a serious illness or a disaster. Interest on the tax still applies.

### What if I pay part of the tax?

The penalty and the interest then run on the smaller balance from the date of the payment. This calculator assumes one payment in full; run it once per unpaid amount and period to estimate partial payments.

### What does this calculator leave out?

The failure-to-file penalty, the higher 1% monthly rate after a notice of intent to levy, interest on the penalty itself after an IRS notice, partial payments, and state penalties. It is an estimate, not tax advice.

## Sources

- IRS, Quarterly interest rates (underpayment rate for individuals, each quarter from 2018 to the fourth quarter of 2026). https://www.irs.gov/payments/quarterly-interest-rates
- IRS, Failure to Pay Penalty. https://www.irs.gov/payments/failure-to-pay-penalty
- 26 U.S.C. 6651 (failure to file or pay; (a)(2) 0.5% a month up to 25%; (h) 0.25% under an installment agreement). https://www.law.cornell.edu/uscode/text/26/6651
- 26 U.S.C. 6621 (rate: federal short-term rate plus 3 points) and 6622 (daily compounding). https://www.law.cornell.edu/uscode/text/26/6622