What is my IRS late payment penalty?
Paying federal tax late costs a penalty and interest. Type the unpaid tax, the date it was due, and the date you pay to see both, at the IRS rates for each quarter.
- Penalty and interest
- $302.82
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.
- Failure-to-pay penalty
- $150.00
- Interest
- $152.82
- Unpaid tax
- $5,000.00
- Total to pay
- $5,302.82
- Months late
- 6
- Days late
- 168
- Penalty as a share of the tax
- 3%
Answer for the example date Wednesday, September 30, 2026. It changes to today's date when the page loads.
Penalty and interest: $302.82. 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.
What makes up the total you owe?
Penalty and interest by unpaid tax
The results are estimates for information only. They are not financial, tax, or legal advice. Check the numbers with your lender or a qualified professional before you decide. Terms of use
How to calculate
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.
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.
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.
- 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
Each example is checked against the calculator on every build.
- Unpaid tax $10,000.00, Payment due date 2025-04-15, Date you pay 2025-10-15, I have an installment agreement no gives Months late 6, Failure-to-pay penalty $300.00, Interest $357.16, Penalty and interest $657.16.Source: IRC 6651(a)(2): 6 × 0.5% × 10,000; interest at 7% (IRS quarterly rates, 2025) compounded daily over 183 days
- Unpaid tax $5,000.00, Payment due date 2024-04-15, Date you pay 2026-09-29, I have an installment agreement no gives Months late 30, Failure-to-pay penalty $750.00, Interest $965.24.
- Unpaid tax $2,000.00, Payment due date 2020-07-15, Date you pay 2025-07-15, I have an installment agreement no gives Months late 60, Failure-to-pay penalty $500.00, Penalty as a share of the tax 25%, Interest $643.41.Source: IRC 6651(a)(2): the penalty stops at 25% (60 months would be 30%)
- Unpaid tax $8,000.00, Payment due date 2025-04-15, Date you pay 2026-04-16, I have an installment agreement yes gives Months late 13, Failure-to-pay penalty $260.00, Interest $578.13.Source: IRC 6651(h): 0.25% a month under an installment agreement
How it works
Months late. Count the months or parts of a month from the due date to the payment date. A month runs from the due date to the same day of the next month (or the last day of a shorter month). When the due date is the last day of a month, each month ends on the last day of the next month, so September 30 to October 31 is one month and January 31 to February 28 is one month (IRM 20.1.2.3.8.4.2). Paying on the same day of a later month ends that month; one day later starts another. Paying on the due date is 0 months.
Penalty = unpaid tax × 0.5% × months, or × 0.25% with an installment agreement, and never more than 25% of the tax.
Interest. Start with the unpaid tax. For each day from the due date up to the day before the payment date, multiply the balance by (1 + r ÷ N), where r is the IRS underpayment rate for that day's calendar quarter and N is the number of days in that year (365, or 366 in a leap year). Interest = final balance − tax. Days late = payment date − due date.
IRS underpayment rates for individuals, percent a year:
| Year | Jan to Mar | Apr to Jun | Jul to Sep | Oct to Dec |
|---|---|---|---|---|
| 2018 | 4 | 5 | 5 | 5 |
| 2019 | 6 | 6 | 5 | 5 |
| 2020 | 5 | 5 | 3 | 3 |
| 2021 | 3 | 3 | 3 | 3 |
| 2022 | 3 | 4 | 5 | 6 |
| 2023 | 7 | 7 | 7 | 8 |
| 2024 | 8 | 8 | 8 | 8 |
| 2025 | 7 | 7 | 7 | 7 |
| 2026 | 7 | 6 | 7 | 7 |
Dates must fall from January 1, 2018 to December 31, 2026, the quarters the IRS has published. A payment date before the due date has no answer.
Total = penalty + interest; total to pay = tax + penalty + interest.
Worked examples by hand
$10,000 due April 15, 2025, paid October 15, 2025. Exactly 6 months: penalty 6 × 0.5% × 10,000 = $300. 183 days at 7%: 10,000 × ((1 + 0.07 ÷ 365)^183 − 1) = $357.16. Total $657.16.
$5,000 due April 15, 2024, paid September 29, 2026. 29 full months to September 15, 2026, plus part of one: 30 months, penalty 15% = $750. Interest compounds daily at 8% through 2024 (÷ 366), 7% in 2025, then 7%, 6%, and 7% in the 2026 quarters: $965.24.
$2,000 due July 15, 2020, paid July 15, 2025. 60 months would be 30%, but the penalty stops at 25%: $500. Interest $643.41.
$8,000 due April 15, 2025, paid April 16, 2026, with an installment agreement. 13 months (one day into the 13th) × 0.25% = 3.25%, $260. Interest $578.13.
Other questions people ask
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.