Interest Calculator – calculate interest on an unpaid invoice

Answer the questions below to determine how much interest and compensation you can charge on your unpaid invoice using our interest calculator.

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

User notice

On 1 December 2024, our interest calculator underwent a significant update. To use the new version, you may need to clear your browser’s cache and cookies. Search online for instructions on clearing your cache and cookies, and refer to the 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, use it as a guide to determine 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?