8% Simple interest calculator

Welcome to the Financial Ombudsman Service’s 8% simple interest calculator.

We may have told you to pay interest on top of – or as part of – a payment to your customer.

For interest awarded to reflect the cost of being deprived of money, the default interest rate we may use has changed from 8% simple per year to time-weighted Bank of England average base rate plus one percentage point, for cases referred to us from 1 January 2026.

Learn more about the Financial Ombudsman’s approach to compensation

See here our calculator for working out interest on a sum using base rate plus one percentage point.

This calculator will help you work out what interest you may need to add to an award, using simple interest at 8% per year.

How to use the 8% simple interest calculator

  1. Enter the capital sum you wish interest to be applied to.
  2. Add the start and end date for the period in question.
  3. Use the ‘add new calculation period’ button to enter additional sums and time frames.
  4. Use the ‘calculate’ button to see the result.
  5. The calculator will give you:
    • the value of interest payable for each sum you enter
    • the total for all sums in a single calculation
    • the option of a detailed breakdown of the calculation – available by using the information link, ‘How was this calculated?’
  6. If a refund has been paid during the calculation period, you should enter the refund amount as a negative figure in the ‘Capital sum’ column. The calculator will then allow for the refund appropriately. In the unlikely event that because of the refund(s) the total interest payable is a negative amounst, the interest amount will be set to zero.
  7. Inputting End date:
    • The calculator will allow the user to input a future date which can be no more than 14 days from today’s date. This is to facilitate administrative lag from the date of calculation to the date of payment. In such instances, the current base rate will be used for the future period.

      If the base rate increases before payment, the firm will have to take this into account. If the base rate falls, the firm has the option to pay the initially calculated amount still.

    • Once an end date is input to the first line, the same end date will automatically be copied to any subsequent lines.

Interest calculator – simple interest at 8% per year

Legal disclaimer

This interest calculator is intended to support firms, inform consumers and promote consistency of application. Firms using the interest calculator to calculate an offer remain responsible for:

  1. the accuracy of any interest payment they make, and
  2. ensuring that their interest rate calculations accord with the terms of the redress awarded by the Financial Ombudsman Service Limited.

The Financial Ombudsman Service Limited accepts no liability for any calculation errors produced by the calculator.

Further support

If you're a financial business – or a professional representative of consumers – and you experience problems using this calculator, please:

If you're a consumer, with a question about a financial award or the way it's been calculated, please contact the relevant business. They will be able to explain how they worked out the interest on the amount. If you can’t sort things out with the business, talk to your investigator and they will do their best to help.