Where it applies: Whole UK

Late payment interest calculator

Free tool from RuleKits – plain-English kits for the UK's new rules.

Business to business only. This is for invoices one business sends to another. You cannot use it to charge interest to a private customer (a consumer). If your contract already sets its own late payment interest, that rate applies instead.

Under the Late Payment of Commercial Debts (Interest) Act 1998 you can claim simple interest at 8% a year over the Bank of England “reference rate”, plus a fixed sum towards your recovery costs (£40, £70 or £100).

Invoice amount (including VAT)

The amount still owed on the original invoice.

When was payment due? We agreed a payment date (for example “30 days from invoice”) We did not agree a payment date

Payment due date

The last day the customer could pay on time.

Date paid (or today if still unpaid)

Bank of England reference rate

Filled in for you from the due date. You can change it.

How it works

When interest starts. Interest runs from the day after the payment was due. With no agreed date, payment is late 30 days after the customer got the invoice or you delivered (whichever is later).
Which Bank of England rate. Use the Bank Rate in force on 30 June (if interest starts between 1 July and 31 December) or on 31 December (if interest starts between 1 January and 30 June). This “reference rate” stays the same for that debt, even if the Bank Rate changes later.
Interest. Amount owed × (8% + reference rate) ÷ 365 × number of days late. It is simple interest, not compound.
Fixed sum. £40 if the debt is under £1,000; £70 for £1,000 to £9,999.99; £100 for £10,000 or more. You can claim it once per invoice. If your reasonable recovery costs are higher, you may claim the difference too.

Reference rates built into this tool

Interest starts between	Bank Rate on	Reference rate	Statutory rate

The Bank Rate is 4.00% since 5 November 2026 (checked on bankofengland.co.uk on 8 November 2026). The next decision is on 17 December 2026. The 31 December 2026 rate in this tool is a provisional figure until then.

If they still do not pay

Scotland: claims of £5,000 or less normally go through simple procedure in the sheriff court (you can use SCTS Civil Online).
England and Wales: claims go to the County Court; you can start a money claim online on GOV.UK.
Northern Ireland: claims go through the courts in Northern Ireland, which have their own procedures.

Before going to court, send a clear letter asking for payment, showing the invoice, the interest and the fixed sum. If you add interest, send a new invoice for it.

Please read: This calculator is general information. It is not legal or financial advice. It assumes the debt is a “qualifying debt” under the Act, that your contract does not set a different interest rate, and that the invoice is not disputed. Check your own situation with GOV.UK's guide to late commercial payments, the Small Business Commissioner, or a solicitor. Rules can change. Last checked: 8 November 2026.

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Sources

The Late Payment of Commercial Debts (Rate of Interest) (No. 3) Order 2002, article 4 – 8% over the rate on 30 June / 31 December (checked 8 November 2026)
Late Payment of Commercial Debts (Interest) Act 1998, section 5A – fixed sums £40 / £70 / £100 (checked 8 November 2026)
GOV.UK: Late commercial payments – charging interest and debt recovery (checked 8 November 2026)
Small Business Commissioner: interest calculator guidance (checked 8 November 2026)
Bank of England: Interest rates and Bank Rate (checked 8 November 2026)