Invoice & Late Fee Calculator

What this does

An invoice late fee calculator works out late-payment interest on an overdue invoice from an annual rate and the days late, plus an optional flat fee and the total now due.

How to use it

1. Enter the invoice amount.
2. Enter the annual interest rate.
3. Enter the days overdue.
4. Add any flat fee.

How it works

Caps on late fees vary by contract and jurisdiction, so check what your agreement and local law allow before billing.

interest = amount × annual rate ÷ 365 × days late

Understanding your result

The interest figure is what the overdue amount has accrued at the annual rate for the days late, added to any flat fee to give the total now due. Use it as a fair, defensible charge, but check your contract and local law first, since allowable late fees vary by jurisdiction.

Example

$1,000 at 8% for 30 days adds about $6.58 in interest.