If another business pays you late, you can claim statutory interest at 8% a year above the Bank of England base rate, plus a fixed sum of £40, £70 or £100 for each late payment. Enter the amount owed, the date it was due and the date you were paid (or today), and the calculator does the rest. It covers business-to-business debts, including public sector customers, but not consumers.
Enter the debt and its dates
Enter the amount owed, the agreed payment date and the date you were paid, or today if you are still waiting. Interest runs from the day after the agreed payment date. If you did not agree one, payment is late 30 days after the customer received the invoice or you delivered the goods or service, whichever is later. An agreed payment date should usually fall within 60 days between businesses (a longer period must be fair to both sides) and within 30 days for a public authority.
The rate
‘Statutory interest’, chosen by default, is 8% plus the Bank of England base rate. If the debt becomes late between 1 January and 30 June, take the base rate in force on the 31 December before; between 1 July and 31 December, the one in force on 30 June. That rate then stays the same until you are paid. For debts that became late in 2026 it is 11.75% (3.75% + 8%). The base rate rose to 4% on 5 November 2026: if it is still 4% on 31 December, debts that become late between 1 January and 30 June 2027 will carry 12%, which the calculator uses meanwhile and marks as provisional. Every rate since 2019 is under ‘Rates by half-year’, below the result.
The fixed sum
‘Add the fixed sum’ is ticked by default. On top of interest, you can claim a fixed sum once for each late payment: £40 for a debt under £1,000, £70 from £1,000 to £9,999.99 and £100 for £10,000 or more. If your reasonable costs of recovering the debt are higher, you can also claim the difference.
If your contract sets a rate
Choose ‘A rate set in the contract’ and enter the annual rate. If your contract gives you a ‘substantial’ remedy for late payment, such as its own interest rate, you claim under the contract instead of statutory interest, and the fixed sum, which comes with statutory interest, is not added. A term that rules out interest, or offers a remedy that is not substantial, is void (sections 8 and 9 of the Act).
Use the result
The total to claim on top of the invoice comes first, then the days late, the date interest runs from, the interest, the fixed sum, the total owed including the invoice, and the workings. If a rate that is not published yet was used, the result says it is provisional. ‘Period and rate used’ shows where the rate comes from. Copy the result, export it as a CSV file or save it to Priostack: the calculation is then kept on this device, under ‘Recent calculations’.
Interest = amount owed × (8% + reference rate) × days late ÷ 365.
Days late run from the day after the due date to the day you are paid. Each day counts for 1/365 of the annual rate, in leap years too, and the result is rounded to the nearest penny.
Total to claim = interest + fixed sum.
