Late payment interest calculator

Find out how much interest you can add to an overdue invoice, at the rate in your contract or at the UK statutory rate for business debts.

Amount owed

Currency

Payment was due

Paid, or today

Interest basis

Rate (%)

For UK statutory interest, use the base rate in force on the day the debt became overdue (check the Bank of England website). This is general information, not legal advice.

Asking for payment

Not sure when the invoice fell due? The invoice due date calculator works it out from terms such as net 30 or 15 MFI.

Send a clear written reminder or demand before adding interest. The free payment reminder letter has an optional late fee line, the payment demand letter has an optional interest paragraph, and the late payment interest clause shows how to put a rate in your next contract.

Add this calculator to your website

Free for blogs, accountants, law firms, trade associations and anyone who helps small businesses. Paste the code where you want the calculator to appear. It runs in your visitors' browsers, with no cookies, no tracking, and nothing they type sent anywhere.

Embed code

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Preview

The last line of the code resizes the calculator to fit; if your site strips scripts, leave it out and the calculator still works at a fixed height. On a dark website, add ?theme=dark after late-payment-interest.html. Please keep the credit line under the calculator.

Questions

How is late payment interest calculated?

Usually as simple interest: the overdue amount × the yearly rate × the number of days late ÷ 365. This calculator counts days from the due date to the payment date.

What is UK statutory interest?

Under the Late Payment of Commercial Debts (Interest) Act 1998, a business owed money by another business can usually claim interest at 8% above the Bank of England base rate, plus a fixed sum of £40, £70 or £100 depending on the size of the debt, unless the contract provides its own substantial remedy. It does not apply to consumers.

Can I charge interest if my contract does not mention it?

It depends where you are. UK businesses have the statutory right above; elsewhere you may need a contract term or a court award. See the late payment interest clause in the clause library.

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