Late Payment Interest Calculator
Work out the statutory interest and fixed compensation you can claim when a business customer pays an invoice late, from the due date, with the right Bank of England reference rate and a summary to send.
About this tool
When one business pays another late, the Late Payment of Commercial Debts (Interest) Act 1998 lets you claim interest at 8% a year above the Bank of England base rate, plus a fixed sum for the cost of chasing it: £40 for a debt under £1,000, £70 from £1,000 to £9,999.99 and £100 for £10,000 or more. Interest runs from the day after payment was due. If no date was agreed, a debt becomes late 30 days after the customer received the invoice or the goods, whichever is later.
The base rate used is the one on 31 December for debts that became overdue between 1 January and 30 June, or on 30 June for debts that became overdue between 1 July and 31 December, and it stays the same for the life of the debt. The calculator picks it from the due date (3.75% for debts that became overdue during 2026); you can change it if your contract sets a different rate. These rights only apply between businesses, not to consumers, and you can also claim reasonable extra costs of recovering the debt if the fixed sum doesn't cover them. Nothing here is legal advice.