IRS Penalty Calculator
Estimate IRS penalties for late filing, late payment, or underpayment of estimated taxes based on the amount owed and how many days past the deadline you are. Helpful for taxpayers deciding whether to file for an extension or pay immediately.
Last updated: May 2026
About this calculator
The IRS imposes three distinct monetary penalties. The failure-to-file penalty accrues at 5% of unpaid tax per month (or partial month) late, capped at 25% of the tax owed. The failure-to-pay penalty accrues at 0.5% per month until the balance is paid. The underpayment-of-estimated-taxes penalty works like interest: the shortfall times the IRS underpayment rate (the federal short-term rate plus 3 percentage points, set each quarter — 6% as of Q2 2026), prorated by the number of late days. The IRS compounds this daily; the calculator uses simple interest, which is a close approximation over typical periods. The formulas used here are: late filing = 5% per month, capped at 25%; late payment = 0.5% per month, capped at 25%; underpayment = taxOwed × 6% × (daysLate ÷ 365); combined = 4.5% per month late-filing (at most 5 months) plus 0.5% per month late-payment (capped at 25%) — when both penalties apply in the same month the IRS reduces the late-filing penalty by the late-payment amount, so the combined charge is 5% per month. Every result is multiplied by reasonableCauseFactor, which is 1 if no reasonable cause applies (penalty stands) or 0 if the IRS accepts a reasonable cause waiver. Importantly, the penalty can be waived entirely if you can demonstrate reasonable cause and lack of willful neglect, so always document extenuating circumstances before they are needed.
How to use
Suppose penaltyType = 'lateFile', taxOwed = $4,000, daysLate = 45, and reasonableExpected = 'no' (waiver not expected). Step 1: Months late = ceil(45 / 30) = 2. Step 2: Penalty rate = 5% per month → 2 × 0.05 = 0.10. Step 3: Raw penalty = $4,000 × 0.10 = $400. Step 4: Check cap: 25% of $4,000 = $1,000; $400 < $1,000, so cap does not apply. Step 5: Reasonable cause factor = 1 (no waiver). Final penalty = $400 × 1 = $400 added to your balance owed. Example 2 — Underpayment of estimated tax: penaltyType = 'underpayment', taxOwed = $10,000, daysLate = 90, reasonableExpected = 'no'. Penalty = 10,000 × 0.06 × (90 / 365) = 600 × 0.2466 = $147.95. Example 3 — Combined penalties: penaltyType = 'combined', taxOwed = $4,000, daysLate = 75, reasonableExpected = 'no'. Months late = ceil(75 / 30) = 3. Late-filing portion = 4.5% × 3 = 13.5%; late-payment portion = 0.5% × 3 = 1.5%; combined rate = 15%. Penalty = $4,000 × 0.15 = $600.
Frequently asked questions
How does the IRS failure-to-file penalty differ from the failure-to-pay penalty?
The failure-to-file penalty is significantly steeper — 5% of the unpaid tax per month or part of a month, up to a maximum of 25% — because the IRS views non-filing as more serious than non-payment. The failure-to-pay penalty, by contrast, accrues at only 0.5% per month on the outstanding balance, also capped at 25%. When both penalties apply in the same month, the failure-to-file penalty is reduced by the amount of the failure-to-pay penalty, so the combined charge is still 5% that month. Filing on time — even without full payment — is almost always the better financial choice.
What qualifies as reasonable cause for the IRS to waive a late-filing or late-payment penalty?
Reasonable cause exists when a taxpayer exercises ordinary business care and prudence but still cannot comply with the filing or payment deadline. Accepted examples include a serious illness or hospitalization, a death in the immediate family, a natural disaster that destroyed records, or an inability to obtain necessary tax records despite good-faith efforts. Simply forgetting the deadline or lacking the funds to pay does not constitute reasonable cause. To request abatement, you submit a written explanation with supporting documentation; first-time penalty abatement is also available to taxpayers with a clean three-year compliance history, regardless of cause.
How can I reduce or stop IRS penalties from continuing to accrue after I miss a deadline?
The most effective way to stop penalties from growing is to file your return as quickly as possible and pay as much of the balance as you can afford immediately. Paying the full amount stops the failure-to-pay penalty from accruing further. If you cannot pay in full, entering into an IRS installment agreement or an offer-in-compromise can reduce the penalty rate on remaining balances. Interest on unpaid tax continues to compound even during a payment plan, so paying ahead of schedule saves money. Requesting a penalty abatement in writing — either for reasonable cause or under the first-time abatement program — can retroactively reduce penalties already assessed.