Late fee calculator
Work out the late fee on an unpaid invoice from the terms in your own contract: a flat fee, or a percentage per month, with grace days if you give them. The result updates as you type.
Nothing you type here is stored on our servers or logged.
Fill in the fields to see the result.
Before you charge a late fee
US states limit late fees and interest differently. Check your state's rules and your contract. Your state's tax or revenue agency is listed on USA.gov.
This calculator applies the terms you enter. It does not check whether they are allowed where you or your client are. A percentage per month is worked out by the day, on the unpaid amount, without compounding, with a month counted as 30 days. That is how MinsoBill adds a late-fee line to reminders, too.
Sources
Last checked November 9, 2026.
This is general information, not legal or tax advice.
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