Late Fee Calculator
How much is actually owed on an overdue invoice? Calculate the late fee and total due in seconds.
When an invoice goes overdue, the amount owed is not just the original total. Most contracts and many local laws allow a late fee, either as a percentage that grows with time or as a fixed charge, and the exact rule depends on what you and your client agreed before the work started. This late fee calculator helps you work out the number to put in a reminder: enter the original invoice amount, how many days it is overdue, and either a monthly percentage rate or a fixed late fee, then subtract any amount the client has already paid. The calculator shows the late fee, the outstanding balance before the fee, and the total now due, so you can quote one clear number instead of guessing. It uses simple pro-rating for percentage fees, meaning the fee grows in proportion to days overdue, and it never charges a fee on money that has already been paid. Always follow your contract and local law, not this calculator alone. This page is general guidance, not legal advice, and you should check the allowed rate, notice requirements, and wording before you charge a late fee to a real client. All calculations run in your browser and nothing is stored.
Your numbers
Amount now due
Recommended tools
Accounting and invoicing software we are reviewing. No recommendation yet — placeholder for vetted picks only.
How to use the result
- Quote the total due as one number, and show the late fee separately so the client can see how it was calculated.
- Only charge a fee your contract allows. If no late fee was agreed, ask for the outstanding balance first.
- Send the reminder in writing, with the invoice number, due date, days overdue, and the fee calculation.
Frequently asked questions
Is a late fee legally allowed?
It depends on your contract and local law. Many places allow a reasonable late fee if it was agreed in advance, but rates, notice rules, and caps vary. Check your contract and local rules — this calculator is not legal advice.
Percentage or fixed fee — which should I use?
Use whichever your contract states. Percentage fees scale with the invoice and time overdue; fixed fees are simpler for small invoices. Do not switch methods after the invoice is overdue.
What if the client already paid part of the invoice?
Enter the paid amount. The fee is calculated only on the outstanding balance, and the total due is outstanding plus fee.