Invoice Late Fee Calculator
See exactly how much a late client owes you — the late fee, the new total due, and how much more piles on every day the invoice stays unpaid.
✏️ These numbers were filled in from a shared link — change anything to make it your own.
How the late fee is calculated
The interest portion is your monthly rate applied to the unpaid amount, pro-rated by how far past due the invoice is:
interest = amount × (monthly rate ÷ 100) × (days overdue ÷ 30)
Any one-time flat fee is then added on top, and a grace period simply delays the day the clock starts. This uses simple interest on the original balance — the most common and easiest-to-defend approach for freelance invoices.
General information only, not legal advice. Some states and countries cap the late fee or interest you can charge, and enforceability is strongest when the fee was agreed in writing beforehand. Check your local rules and contract terms.
Frequently asked questions
How do I calculate a late fee on an overdue invoice?
Multiply the unpaid amount by your monthly late-fee rate, then scale it by how far past due the invoice is: fee = amount × (monthly rate ÷ 100) × (days overdue ÷ 30). Add any one-time flat fee. For example, a $2,000 invoice at 1.5% per month that is 30 days late accrues about $30.
What is a reasonable late fee to charge?
Most freelancers and small businesses charge 1% to 1.5% per month (roughly 12–18% per year) on the overdue balance, sometimes with a small flat fee. Some states cap the maximum interest you can charge, so check your local rules before setting a high rate.
Can I charge a late fee if it was not in my contract?
It is much easier to enforce a late fee that you stated up front on the contract or invoice ("1.5% per month on balances over 30 days"). Without a prior agreement, collecting a late fee is harder and varies by jurisdiction. Best practice: put your late-fee policy on every quote and invoice from the start.
Should I use a flat fee or a percentage?
A percentage scales fairly with the invoice size and the length of the delay, which most clients accept as reasonable. A small flat fee is simple and works well for tiny invoices. Many businesses combine both: a modest flat fee plus monthly interest.
How do I ask a client to pay a late fee?
Send a polite reminder that references your agreed terms, shows the original amount, the late fee, and the new total, and gives a clear new due date. Keeping it factual and citing the terms they agreed to makes it feel routine rather than personal.