Free late fee calculator
This free late fee calculator works out the fee your own agreed terms produce on an overdue invoice: enter the amount, the due date and the fee shape from your contract — a monthly percentage, a flat fee or a daily percentage — and it counts the days overdue, the fee and the total now owed. One rule comes before any number: a late fee is only chargeable if it was agreed in writing before the work started. This tool does the arithmetic on a fee that was agreed; it cannot create the right to charge one.
The invoice and your terms
The numbers are only half of it — the rules decide whether a fee exists at all. Our guide to freelance payment terms covers agreeing the clause before work starts, and the guide to asking for late payment professionally covers what to do when one falls due.
What your terms produce
The late fee — chargeable only if this fee was agreed in writing before the work started.
| Invoice amount | $0.00 |
| Days overdue | — |
| Grace period | 0 days |
| Fee basis | — |
| Late fee | $0.00 |
| Total now owed | $0.00 |
Enter the invoice, its due date and your agreed fee shape, and the fee line appears here.
Pick the invoice’s due date and the date to calculate to, and the count starts.
Worked example
Invoice WK-1042 from our late payment email generator’s worked example — $1,450, due 20 October 2026 — checked on 17 November 2026, with the 1.5%-a-month late-fee clause from the agreed terms and no grace period. The calculator above opens with these same figures, so the number on the page when you arrived is this one:
| Invoice amount | $1,450.00 |
| Due 20 October 2026 · checked 17 November 2026 | 28 days overdue |
| Fee: $1,450 × 1.5% × 28 ÷ 30 | $20.30 |
| Total now owed | $1,470.30 |
| The fee as a share of the invoice | 1.40% |
Read the fee at its real size: $20.30 is nobody’s windfall. Its value is that the terms turn out to be real — and the order matters. The clause sat in the proposal before the work started, which is why this is arithmetic rather than an argument. If your own terms carry no late-fee clause, the honest output for your invoice is $0: chase it with the ladder in our late payment guide, and put the clause in place for the next project with the payment terms guide.
How the number works
- The day count. The fee runs on the days between the invoice’s due date and the date you calculate to — not the date you sent the invoice, and not the day you noticed. Grace days, if your terms allow them, come off the count before the fee starts: 28 days overdue with a 7-day grace period is 21 days of fee.
- A monthly rate is charged by the day. This calculator’s convention is pro-rata: the fee is the invoice amount × the monthly rate × days, divided by 30. It is the fair reading of “1.5% per month” for part of a month — stated here plainly so you can check it against your own agreement. Some agreements instead charge for each month or part month begun; if yours says that, its wording governs, not this page.
- Flat and daily shapes behave differently. A flat fee lands once, whole, the day the grace period ends — heavier on small invoices, lighter on long delays. A daily rate looks tiny and is not: 0.05% a day is roughly 1.5% a month, accumulating every single day the invoice sits unpaid.
- Compounding is off unless your agreement turns it on. Simple terms charge the percentage on the invoice balance; compounded terms add each month’s fee to the balance before the next month is calculated. The second needs its own sentence in the terms the client accepted — which is why the switch in this calculator is off by default and labelled the way it is.
- The agreement is the real input. Everything on this page is arithmetic. Whether a fee can be charged at all was settled earlier — in the proposal or contract, before the work started. Our guide to freelance payment terms shows where the clause belongs; our guide to asking for late payment professionally covers the follow-up when one falls due, and the late payment email generator turns it into wording.