Free tool
Late fee calculator
Flat fee, monthly percentage, or annual APR. We do the math, flag any state usury cap, and give you wording you can paste into a follow-up email.
A late fee on an unpaid invoice is enforceable when three things are true: the fee is in the original contract or terms of the invoice, the rate is reasonable under your state's usury law, and the fee is calculated transparently. This calculator handles the math for the three most common structures (flat fee, monthly percentage, annual APR) and flags the rate against the state cap you select. Always check with a lawyer for high-value disputes.
Late fee
$0.00
Total now owed
$0.00
Effective APR
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Copy late-fee wording for your follow-up
The four mistakes that make a late fee uncollectable
Late fees are easy to set up and easy to lose in a dispute. Here is what trips most senders.
The fee was not in the original contract or invoice
Adding a late fee after the fact is unenforceable in almost every jurisdiction. The clause has to be on the original invoice or in a signed agreement.
The rate exceeds your state's usury cap
States cap interest rates on commercial debt. New York is 16%, California's general civil cap is 10%, Texas allows 18% for written contracts. Above the cap, the entire late fee can be voided.
Compounding without saying so
1.5% per month sounds the same as 18% APR but compounds to 19.56%. Either calculate as simple interest or state 'compounded monthly' on the invoice.
Charging more than the contract states
If your invoice says '1.5% per month' you cannot suddenly charge 2%. Stick to the documented rate or send a new agreement.
Use the result downstream
Late fee FAQ
Can I charge a late fee without warning?
What is a reasonable late fee in the US?
What is the usury limit?
Can I charge a late fee on a B2B invoice?
Is it better to charge a flat fee or a percentage?
What if the client pays the original invoice but ignores the late fee?
Send the late fee with a real, dated invoice
Make a follow-up invoice for the fee in seconds. Your client opens the link, sees the breakdown, and can approve and pay through the channels you list.
Open the invoice generatorNo signup required. Build now, save later.