Invoice calculators · Updated August 27, 2026
Invoice Late Fee Calculator
Enter the invoice amount and the fee your terms name — flat, one-time percentage, or a monthly percentage — and see the fee and the new total. Free, in your browser.
Late fee
How the fee is calculated
A monthly percentage — the most common structure, typically 1–2% — is pro-rated by days: 1.5% per month on a $1,000 invoice that is 45 days overdue is $1,000 × 1.5% × (45 ÷ 30) = $22.50. A one-time percentage applies once, whatever the delay; a flat fee is just the number your terms name.
Two rules keep a late fee enforceable in practice: the client agreed to it before the work (it is on the estimate and the invoice, not invented after), and it fits your local rules — several states cap interest on overdue balances. The late fee guide covers structures, wording you can copy, and the alternatives that often work better than a fee.
Late fee FAQ
Can I add a late fee to an invoice I already sent?
Only if the client agreed to the fee before the work — on the estimate, the contract, or the original invoice. A fee that first appears on a reminder reads as a penalty invented after the fact, and usually is not enforceable.
What rate is normal?
1–2% per month is the common range. Several states cap the rate — check your local rules before printing anything bigger.
How do I show it on the invoice?
As its own line ("Late fee — 1.5% per month, 45 days past due — $22.50") on an updated invoice, never silently folded into the total. The generator's editable labels make the line read exactly how you want.
