Late Payment Interest Calculator
Work out the interest and fees owed on an overdue invoice, day by day.
Enter the unpaid amount, the interest rate, the due date and the payment date. The calculator counts the days late, applies simple interest per day on a yearly or monthly rate, and adds a fixed late fee if you charge one.
How late payment interest is calculated
Simple interest = amount × rate × days late ÷ 365 for a yearly rate, or ÷ 30 for a monthly rate. Example: 1,000 at 10% a year, paid 60 days late, gives 1,000 × 10% × 60 ÷ 365 = 16.44 in interest.
Which rate can you charge?
The rate should be written in your contract or on the invoice. Without one, the law of your country applies. In the European Union, the statutory rate between businesses is the European Central Bank reference rate plus at least 8 percentage points, plus a fixed compensation of at least 40 euros per invoice. In the United States, the rules differ from state to state. This calculator is not legal advice: check the rate that applies to you.
Questions about the Late Payment Interest Calculator
Can I charge interest on a late invoice?
Usually yes, when the rate and conditions are stated in the contract or terms you agreed with the client. Many countries also set a statutory rate for late payment between businesses. Sales to consumers often have stricter limits.
Simple or compound interest?
Late payment interest is normally simple interest, counted per day on the unpaid amount. That is how this calculator works.
How do I ask the client to pay the interest?
Add it as a line in a payment reminder, with the number of days and the rate used. Our payment reminder generator lists the overdue invoices and the total due.