Invoice Late Fee Calculator

Calculate interest and fees on an overdue client invoice. Everything runs in your browser; nothing is uploaded.

Works in any currency: enter amounts in your own currency (USD, EUR, GBP, INR…).

Invoice

Invoice amount

Days past due date

Grace period (days)

Late fee terms

Interest per month (%)

Flat late fee

Results

Total late fee

Interest

Flat fee

New amount due

Days charged

Annual rate equivalent

How invoice late fees are calculated

Interest is charged as simple interest on the invoice amount for the days beyond the grace period: interest = amount × monthly rate × (days late − grace) ÷ 30. A flat fee, if your terms include one, is added once the grace period has passed.

Late fees must be stated in your contract or invoice terms before the work, and many places cap the rate (some US states limit it; the EU Late Payment Directive and UK late payment law set statutory interest for B2B invoices). Check local rules before charging.

FAQ

What is a typical late fee?

1–2% per month is common, sometimes with a small flat fee.

Can I add late fees without agreeing them first?

Generally you should include them in your contract or invoice terms; some jurisdictions give statutory B2B interest anyway.

Should I offer a grace period?

A short grace period (e.g. 5–15 days) keeps relationships friendly while still encouraging payment.