Owed Tax and Missed the Deadline? Rough Penalty + Interest Sketch
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Many taxpayers confuse “extension to file” with “extension to pay.” If you owe federal tax and file or pay after the due date, the IRS may apply failure-to-file and failure-to-pay penalties plus interest. This estimator is intentionally simpler than IRS worksheets—it helps you see the order of magnitude before you pull transcripts or call a CPA.
Ready to run the numbers?
Why: Domestic filers need a different narrative than expats; both overlap on unpaid tax but not on overseas deadlines.
How: Enter unpaid tax, months you model for each penalty, days for a simple interest estimate, and an annual interest rate.
Run the calculator when you are ready.
You entered more than 60 days late for interest—the IRS may impose a minimum failure-to-file penalty for very late returns. Confirm with IRS instructions or a pro.
Stacked (single scenario)
Share of illustrative total
Penalties vs months (same months for both)
Sweep uses equal FTF/FTP months 0–12 at your unpaid tax amount
For educational and informational purposes only. Verify with a qualified professional.
Domestic vs expat tools
This page focuses on common Form 1040 filers in the U.S. with tax due. If you are abroad, payment deadlines and credits differ—use the US Expat IRS Penalty Risk Calculator for FEIE/FTC context.
How estimates are built
FTF ≈ min(5% × months × unpaid, 25% × unpaid)
FTP ≈ min(0.5% × months × unpaid, 25% × unpaid)
Interest ≈ unpaid × (annual% ÷ 365) × days
Frequently asked questions
Who is this calculator for?
US taxpayers who file a Form 1040 with a balance due and want a rough sense of failure-to-file and failure-to-pay penalties before extensions. It is not tailored to expats—see our US Expat IRS Penalty Risk Calculator for payment-deadline issues abroad.
What penalties does it model?
Failure-to-File (FTF): typically 5% of unpaid tax per month or part of a month, capped at 25% of unpaid tax. Failure-to-Pay (FTP): typically 0.5% per month or part of a month, capped at 25%. If both apply in the same month, the IRS coordinates rates—this tool shows separate caps and a combined illustrative total with a disclaimer.
Does it include interest?
It adds simple interest on the unpaid tax for the days you enter using an annual rate you choose (often near IRS underpayment rates in recent years). Actual IRS interest compounds daily and applies to penalties as well in many cases—this is a lower-complexity estimate.
What about the minimum penalty if I am more than 60 days late?
For returns due in 2023–2025, if you file more than 60 days late there is a minimum penalty (see IRS instructions). This calculator flags when your lateness exceeds 60 days but does not replace the IRS worksheet for the minimum.
Can I avoid penalties with an extension?
Form 4868 extends time to file, not time to pay. If you owe tax, you generally must still pay by the original due date to avoid failure-to-pay and interest. If you pay at least 90% of the current year tax with the extension, you may reduce some underpayment issues—confirm with IRS Pub 17 or a pro.
Is this tax or legal advice?
No. Use IRS.gov, your notice, or a licensed tax professional for your situation.
Simplified illustration. IRC coordination between penalties, daily compounding interest, first-time abatement, and reasonable cause are not modeled.
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