Calculate interest on an unpaid invoice

Answer the below questions to work out how much interest and compensation to charge on your unpaid invoice.

  • You cannot charge late payment interest until your invoice becomes overdue.
  • Unless terms are agreed, both public and private sector payment terms are 30 days.
  • For guidance on our calculator and how to use it, please visit our interest calculator guidance page.
  • To calculate the late payment interest due on your overdue invoice, please input the date that the invoice was due for payment.

User notice

On 1 December 2024, our interest calculator underwent a significant update. If you used our calculator prior to 6 July, you may need to delete your browser’s cache and cookies to use the new version. Search online for guidance on how to clear your cache and cookies, we’ve listed links below for some of the most popular browsers:

Our interest rate calculator calculates interest to the first two decimal points only.

While this gives a fairly accurate figure it should be used as a guide to the amount of interest and compensation you can charge on overdue invoices.

If you want a more accurate figure, please carry out a manual calculation.

Please note you can only collect interest on a late payment up to a maximum of 6 years from the from date following end of contracted payment terms.

Do you have contracted payment terms?
What are your contracted payment days from date of invoice as per the contract?
What was the date invoice received by respondent?
If the overdue invoice has been paid, what was the date of payment?
What was the date invoice received by respondent?
If the overdue invoice has been paid, what was the date of payment?