This late payment interest calculator works out the interest on an overdue invoice from the amount, the due date and your yearly rate.
Enter your yearly interest rate to see the interest.
Multiply the unpaid amount by your yearly rate, then by the number of days late, and divide by 365. The days late start the day after the due date and run until the day you are paid.
For example, 1,000 at 10% a year, paid 30 days late, works out as 1,000 x 0.10 x 30 / 365 = 8.22. The calculator above does the same sum, shows the interest per day, and adds any fixed late fee to give the new total.
Use it to work out the interest on an unpaid invoice before you send a reminder, so the figure in your email matches your terms.
That depends on two things: what your contract or invoice terms say, and the law in your country. Some countries set a statutory rate for late business payments, others leave it to the agreement. That is why the calculator has no default rate: you enter the one that applies to you.
Whatever you charge, state your late payment terms on every invoice, for example "Interest of 8% a year is charged on overdue amounts." A client is far more likely to accept interest they were told about before the due date passed.
If a client pays in parts, work out the interest on each unpaid balance for the days it was outstanding, then add the amounts together.
You can charge either, or both if your terms allow it. Here is how they compare:
| How it works | Best for | |
|---|---|---|
| Interest | Grows every day the invoice stays unpaid, as a percentage of the amount | Larger invoices, and clients who pay very late |
| Fixed late fee | One set amount, charged once the due date has passed | Small invoices, where the interest would only be a few cents |
The tool also works as a simple late fee calculator: leave the rate blank and enter only a fixed invoice late fee to see the new total.
When you send the reminder, show the original amount, the days late, the interest and the new total on separate lines, so the client can check each number for themselves.
Yes. It is free to use, with no sign-up, and the numbers you enter stay in your browser.
It depends on what your contract or invoice terms say and on your country's law. Enter the rate that applies to you. The calculator does not assume one.
Usually simple interest, worked out per day on the unpaid amount. This calculator uses simple interest.
In some countries the law lets a business charge interest on late business payments anyway. In others you can only charge what your terms allow. Check your local rule before you add it.
On the day after the due date, and it runs until the day you are paid.