Late payment fee calculator

Enter the unpaid amount, the annual interest rate in your terms and how many days the invoice is overdue.

Invoice amount outstandingAnnual interest rate%Days overdueFixed late fee (if any)

Interest a day: 0.55
Interest over 30 days: 16.44
Fixed fee: 0.00
Total now owed: 2,516.44

How it's calculated

The annual rate is divided by 365 to get a daily rate, multiplied by the amount outstanding, then by the days overdue. Simple interest, not compounding — that's the usual reading of a "% per annum" clause unless your contract says otherwise. Days overdue are counted from the day after the due date.

You can only charge what you agreed

A late fee is enforceable because it's in your contract or on your invoice before the work started, not because you added it afterwards. What rate is permitted, whether a statutory rate or fixed compensation applies, and how it works for consumers versus businesses all vary by country and sometimes by state. Check your own jurisdiction — nothing here is legal advice.

Before you send the fee

In most cases a plain reminder recovers the money faster than a charge does. Work through the follow-up sequence first, and keep the fee as the step that shows you're serious. If you do apply it, issue it as a clearly itemised line on a new invoice with the original invoice number referenced.