IRS Penalty and Interest Calculator

What this calculator does not model

• Fraud penalties: fraudulent failure to file (IRC §6651(f)) and the civil fraud penalty (IRC §6663).
• Accuracy-related penalties (IRC §6662).
• Penalties for late or wrong information returns and payee statements, such as Forms W-2 and 1099 (IRC §6721, §6722).
• The estimated tax penalty for individuals (IRC §6654).
• Tax the IRS adds after you file, from an exam or a math-error notice, and its own failure-to-pay penalty (IRC §6651(a)(3)).
• Penalty relief: first-time abatement, reasonable cause, and the other ways to remove a penalty. The calculator shows what accrues before any relief. Penalty relief paths.
• Mandatory COVID-19 relief for returns and payments originally due January 20 through March 20, 2020 (Abdo v. Commissioner, 162 T.C. 148; IRM Procedural Update SBSE-20-0726-0731 of July 27, 2026, which adds IRM 20.1.1.3.3.7). The form refuses those due dates. One federal court (Kwong v. United States, 179 Fed. Cl. 382 (2025)) read that relief to run through July 10, 2023. The IRS does not follow that ruling, and the calculator follows the IRS.
• Disaster postponements (IRC §7508A) and combat-zone extensions (IRC §7508), other than the nationwide COVID-19 dates the form tells you to enter.
• Interest the IRS pays you on an overpayment (IRC §6611).
• State penalties and interest, and any return other than an individual income tax return.

How the calculator reads the rules

• IRC §6651(b)(2) and Treas. Reg. §301.6651-1(d)(2)(i) reduce each month’s failure-to-pay base by tax paid on or before the first day of the month. IRM 20.1.2.3.8.4.1, which IRS systems follow, counts only tax paid before the month begins. The calculator follows the IRM, so a payment on the first day of a penalty month still carries that month’s penalty; the Code and the regulation support removing it.
• Neither the Code nor the IRM defines the “business days” in the 10-day window for bills of $100,000 or more. The calculator skips weekends and District of Columbia legal holidays, the base definition in IRC §7503; it does not model the statewide holidays §7503 also excuses.
• When a payment covers the bill within 21 days (10 business days at $100,000 or more), the IRS treats it as paid on the bill date for interest (IRC §6601(e)(3)) and charges no further failure-to-pay penalty on it (IRM 20.1.2.3.8.2). The calculator does the same.

Related

• Want the IRS to remove these penalties? The Penalty Abatement Letter Builder drafts the request from your own facts. Ask for relief
• Check whether first-time abatement or reasonable cause could remove these penalties. Penalty Abatement Analyzer
• Read how the relief paths work before you ask for one. IRS penalty relief, explained
• See every quarterly rate the calculator uses. IRS interest and penalty rates
• Find Form 843, the form for asking the IRS to abate a penalty or refund one you paid. Form Finder