Free tool · Interest Calculator

Simple interest calculator

Work out the interest owed on an unpaid debt — at any rate, between any two dates. Enter the amount, the rate and the dates, and the calculator shows the number of days, the interest, the daily rate, and the total now due.

⏱ Updates as you type 🔒 Nothing is saved or sent
£
% a year
The date the debt fell due.
Defaults to today.
This is a commercial (B2B) debt Adds the statutory fixed compensation a business can claim for a late-paid debt under the Late Payment of Commercial Debts (Interest) Act 1998 (£40, £70 or £100, depending on the size of the debt).
Any further fixed amount you want to add — for example a court issue fee or administration cost.
£
Where this sits Business Disputes at Robertsons → If the debt won't be paid Commercial debt recovery at Robertsons → For larger or disputed claims Commercial litigation at Robertsons →

Chasing a debt that won't be paid?

Working out the interest is the easy part. When a debtor still won't pay, our team handles the formal escalation — the Letter Before Action, court issue and enforcement. Leave your details and we'll call you back. No obligation, no charge for the call.

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This is a general calculation, not legal advice. It works out simple interest on a 365-day year and is intended as a quick guide. The right rate and the right dates depend on your contract, the type of debt and the rules that apply — and a variable or tracker rate has to be worked out period by period. To know what you can actually recover, speak to a solicitor. Robertsons Solicitors is authorised and regulated by the Solicitors Regulation Authority (SRA No. 625915).