Late Payment Fee and Interest Calculator
Add interest and a flat fee to an overdue invoice and see the total you can ask for.
- Days overdue
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- Original invoice
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- Interest so far
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- Flat late fee
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- Interest per day
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How the total is calculated
Simple interest: amount × yearly rate ÷ 365 × days overdue, plus any flat fee once the invoice is past due.
Can I charge any rate I want?
Not necessarily. Many places cap late fees or interest, and a charge normally needs to be in your contract or invoice terms before the work starts. Check your local rules or ask a lawyer. This tool only does the arithmetic.
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