Invoice Late Fee Calculator

Enter the invoice amount, due date and payment date to get the exact late fee, whether you charge a monthly rate, an annual rate or a flat fee.

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Check your invoice terms and local usury/interest-rate caps before charging; this is a calculator, not legal advice.

How to calculate a late fee that actually holds up

A late fee only sticks if it was in your payment terms before the invoice went out, so state the rate (or flat amount) on every invoice, not just the ones that go overdue. Two methods dominate: a simple monthly rate (1-2% is common among freelancers and small agencies) applied to the days overdue divided by 30, or an annual APR-style rate that some jurisdictions require you to disclose. A flat fee is simplest to explain but doesn't scale with how overdue or how large the invoice is.

Before charging the maximum your terms allow, check your local usury or commercial-interest caps — many regions cap interest on unpaid invoices regardless of what the contract says. And weigh the relationship: a first-time late payer from a good client is often better handled with a reminder than a fee; save the charge for chronic late payers where the fee is the incentive that actually changes behavior.

FAQ

Is a late fee only valid if it was in my original terms?

In most jurisdictions, yes — you generally can't add a late fee retroactively to an invoice that didn't disclose one. Put the rate or flat amount in your invoice template and contract before you need to enforce it.

Monthly rate, annual rate, or flat fee — which should I use?

Monthly simple-interest (1-2%) is the most common for freelancers and small businesses because it's easy to explain and scales with how late the payment is. Flat fees work for consistently small, predictable invoices. Annual APR-style rates show up more in contracts that need to state a disclosed interest rate.

Can I charge whatever late fee I want?

No — many regions cap the interest rate you can legally charge on overdue commercial invoices (usury laws), independent of your contract terms. Check your local cap before setting the rate field above.

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