IRS penalty calculator: late filing and late payment

Calculator

How is the IRS late penalty calculated?

Two penalties and interest, each figured on the tax you haven't paid by the original due date. The calculator applies the Internal Revenue Code rules the way the IRS's own manual computes them:

• Late filing (failure to file): 5% of the tax unpaid on the original due date, for each month or part of a month the return is late, up to 25%. The months count from the filing deadline including a valid extension, and payments made after the due date don't shrink it.
• Late payment (failure to pay): 0.5% of the tax still unpaid for each month or part of a month after the original due date, up to 25%. An extension doesn't move that date. The rate is 0.25% for an individual who filed on time while an IRS payment plan is in effect, and 1% starting 10 days after an IRS notice of intent to levy.
• Both in the same month: the late-filing penalty is reduced by that month's late-payment penalty, so the pair is 4.5% + 0.5%. Late filing stops at 22.5% after five months; late payment keeps running to 25%, a combined 47.5%.
• Minimum penalty: an income tax return more than 60 days late (counting extensions) owes a late-filing penalty of at least the lesser of $535 or the unpaid tax, for returns due in 2027 ($525 for returns due in 2026).
• Partnerships and S corporations: $260 per partner or shareholder for each month or part of a month a Form 1065 or 1120-S is late, up to 12 months, for returns due in 2027, whether or not any tax is owed.
• Interest: the federal short-term rate plus 3 percentage points, set each quarter and compounded daily, on unpaid tax from the original due date until it's paid (7% for October–December 2026).
• Counting months: a month runs from the day after the due date through the same date the next month, so a return one day into a new month owes that month in full. When a deadline falls on a weekend or holiday, the next business day is on time; after that, the IRS counts from the original date.

A worked example

Say a C corporation owes $10,000 with its 2026 Form 1120, pays nothing by April 15, 2027, and files and pays on July 15, 2027, three months late. Both penalties apply in each of those months, so the combined rate is 5% (4.5% + 0.5%).

Late filing is 3 × 5% × $10,000 = $1,500, less the $150 late-payment penalty for the same months. Interest adds $176.04 in both cases. The same numbers for a Form 1040 are in the penalties guide.

What does an extension change?

The filing deadline. A timely extension moves it six months, to October 15, 2027 for Forms 1120 and 1040 and September 15, 2027 for Forms 1065 and 1120-S (for 2026 calendar-year returns). A return filed by then owes no late-filing penalty, and if it's later, the months and the 60-day minimum count from the extended date.

Not the payment date. The late-payment penalty and interest run from the original due date on anything unpaid, which is why the calculator shows them in both columns.

One rule helps if you pay most of the tax on time. An individual on Form 4868 who pays at least 90% of the tax by the original due date, and the rest with a return filed by the extended date, owes no late-payment penalty for the extension period. A corporation on Form 7004 that pays at least 90% by the original due date and the rest by the extended date owes none either. Interest still applies.

The extension itself must be filed by the original due date; a late one has no effect. If yours has passed, read what to do after a missed extension deadline.

What does the calculator leave out?

It estimates the two late penalties and interest for a calendar-year return. It doesn't cover:

• Fiscal years. Due dates for other year-ends are in the fiscal-year guide.
• Estates and trusts (Form 1041). Their 5½-month extension ends on September 30, so the late-filing and late-payment months don't line up the way they do for other returns. We leave them out rather than approximate; see the Form 1041 guide.
• Tax-exempt organizations. A late Form 990 is penalized per day instead; see the nonprofit extension guide.
• Partial payments. It assumes one payment of the balance. Paying part sooner lowers the late-payment penalty from the next month on.
• Interest on penalties. The IRS also charges interest on some penalties; the estimate covers interest on the tax.
• Large corporate balances. A C corporation that owes more than $100,000 can be charged the federal short-term rate plus 5 points instead of 3 once the IRS has notified it; the estimate uses the standard rate.
• Everything else. The 1% rate after a notice of intent to levy, estimated-tax penalties (Forms 2210 and 2220), accuracy-related penalties, disaster and combat-zone postponements, and relief such as reasonable cause or the IRS's Automatic Exemption from Penalty (see the penalties guide).

Dates after October–December 2026 use that quarter's 7% rate until the IRS publishes the next one.

Penalty calculator FAQ

Sources

• IRS: Failure to file penalty (rates, the minimum penalty and per-owner amounts by year)
• IRS: Failure to pay penalty (rates, payment plans, the combined-month rule)
• IRS: Quarterly interest rates
• Internal Revenue Manual 20.1.2, Failure to File / Failure to Pay Penalties (how the months and amounts are computed)
• Revenue Procedure 2025-32 (penalty amounts for returns due in 2027) (PDF)
• Form 4868 and its instructions (the individual 90% rule) (PDF)
• Instructions for Form 7004 (the corporate 90% rule and interest) (PDF)
• 26 U.S. Code § 6651, Failure to file tax return or to pay tax