The Interest on arrears calculator
How much interest has built up on money owed to you, worked out for the exact number of days rather than by the month, so the figure survives being checked.
The invoice and the delay
Everything is worked out in your browser. No figure is sent anywhere.
How to use the Interest on arrears calculator
- Type what is owed, the date it fell due and the date it was settled, then the annual rate from your contract.
- Type your own numbers. The result updates as you type.
- Copy the result, or change an assumption and watch what it does.
Frequently asked questions
How is the interest worked out?
As simple interest on the amount outstanding: the annual rate divided by 365, multiplied by the number of days between the due date and the date of payment, multiplied by the amount. Simple, not compound, because that is what commercial debt rules and most contracts specify. The daily figure is shown so you can carry it forward while the invoice stays unpaid.
How exact is it?
The arithmetic is exact and rounded the way money is, at the cent. What it cannot know is anything specific to you, so read it as the ordinary case rather than as advice.
Is anything uploaded?
Every figure is worked out in your browser. Nothing is uploaded, there is no sign-up, and no result is stored anywhere but on your own device.
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