Statutory interest accrues at 8 percentage points above the reference rate, as simple (non-compounding) interest on the unpaid amount, from the day payment became late until it is paid. The reference rate is the Bank of England Bank Rate in force on 31 December (for interest that starts to run from 1 January to 30 June) or on 30 June (for interest that starts to run from 1 July to 31 December), and it stays fixed for the life of the debt.
Fixed compensation under s.5A is a single sum per invoice — £40 below £1,000, £70 from £1,000, and £100 from £10,000 — recognising the cost of having to chase. It is in addition to the interest.
You do not need to go to court to ask for either: you can set them out in a reminder or a Letter Before Action, and many debtors pay once they see the figure. If a claim does reach the County Court, whether interest and costs are awarded is at the court's discretion.
Work out the interest and compensation on your invoice with the free calculator.