Late payment interest calculator

A client who pays late owes you more than the invoice. Put in the amount, how many days late it is and the base rate, and this shows the interest and the fixed sum the law lets you add.

Late payment interest calculator

What the law allows

Under late payment legislation, a business that pays another business late owes statutory interest at 8 percentage points above the Bank of England base rate, plus a fixed sum for recovery costs: £40 on a debt up to £999.99, £70 from £1,000 to £9,999.99 and £100 from £10,000. The fixed sum is once per late payment.

Business to business only

This is for invoices between businesses. It does not apply to a private individual who is a consumer. And if your contract sets its own late-payment terms, those apply instead.

Which base rate to use

The statute fixes the rate by the base rate in force on 30 June or 31 December before the payment became overdue, not today's. Bank Rate was 3.75% when this was checked. Look up the right date on the Bank of England site before you invoice the interest.

Figures for the 2026/27 tax year, checked 25 October 2026. Sources: Charging interest on late commercial payments; Claiming debt recovery costs; Bank of England: Bank Rate. An estimate, not advice. SideTill is not tax software.

Keep the number for every month

SideTill is the simple record of your side hustle: log the job, send the invoice, record the money when it comes in, and see whether the month actually made you money. It also shows your best month, so you can tell a bad month from a bad habit.

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