Late Payment Interest Calculator
Calculate interest on an overdue invoice from the amount, annual rate, and days late. You set the rate; the math is done for you.
Everything runs in your browser. No data is uploaded or stored.
About this tool
A quick utility: A calculator for the interest owed on a late invoice.
Enter the outstanding amount, the annual interest rate your contract or local law allows, and how many days the invoice is overdue. It computes simple interest on a daily basis — the usual method — and shows the running charge and the new total.
You supply the rate, because what you can charge depends on your agreement and jurisdiction; the tool never assumes a figure.
How to use it
- Enter the overdue invoice amount.
- Enter the annual interest rate you are entitled to charge, and the days overdue.
- Read the interest accrued and the total now due.
Frequently asked questions
Does it store the invoice?
No. The calculation is local to your browser.
What interest rate can I charge?
It depends on your contract and local law — some places grant suppliers a statutory rate plus a fixed recovery fee. Enter the rate that applies to you; the tool does not assume one.
Is this simple or compound interest?
Simple daily interest: amount × rate × days ÷ 365. That is the common method for commercial late payment. Compounding, where allowed, would be slightly higher.