Work out the statutory interest and fixed sum you can add to a late invoice from another business. Enter the amount and two dates, and the calculator applies the rate the law sets for the day the interest started to run.
Statutory interest is simple interest, so it is charged on the amount of the invoice only and never on interest already added.1 It runs from the day after the agreed payment date.3
The rate is 8% a year over the Bank of England base rate.5 Which base rate counts depends on when the interest started to run, not on when you claim it:5
The calculator multiplies the amount by the rate to get a year’s interest, divides by 365 for a day’s interest and multiplies that by the number of days late.7 It then adds the fixed sum for the cost of chasing, which the Act sets by the size of the debt:8
You can charge the fixed sum once for each payment.9 If your reasonable costs of recovering the debt are higher, you can claim the difference as well.8 The calculator leaves those costs out, because only you know them.
These are the rates the calculator uses. Each base rate is the Bank of England rate in force on the reference date.6
| Interest started to run | Base rate | Statutory rate |
|---|---|---|
| 1 July to 31 December 2026 | 3.75% | 11.75% |
| 1 January to 30 June 2026 | 3.75% | 11.75% |
| 1 July to 31 December 2025 | 4.25% | 12.25% |
| 1 January to 30 June 2025 | 4.75% | 12.75% |
| 1 July to 31 December 2024 | 5.25% | 13.25% |
| 1 January to 30 June 2024 | 5.25% | 13.25% |
| 1 July to 31 December 2023 | 5% | 13% |
| 1 January to 30 June 2023 | 3.5% | 11.5% |
| 1 July to 31 December 2022 | 1.25% | 9.25% |
| 1 January to 30 June 2022 | 0.25% | 8.25% |
| 1 July to 31 December 2021 | 0.1% | 8.1% |
| 1 January to 30 June 2021 | 0.1% | 8.1% |
| 1 July to 31 December 2020 | 0.1% | 8.1% |
| 1 January to 30 June 2020 | 0.75% | 8.75% |
The rate for interest that starts to run from 1 January 2027 depends on the base rate on 31 December 2026. We will add it to this page in January.
Send the customer a new invoice for the interest and the fixed sum.7 Show the original invoice number, the amount, the date it fell due, the rate and the number of days, so they can check the figure against the table above.
Our guide to unpaid invoices and the Late Payment Act covers the rest: who the Act applies to, payment terms, what happens if the customer still does not pay and the changes now going through Parliament.
Adding interest helps once an invoice is late. It does nothing to stop the next one going late. That usually happens because chasing falls to the person who also does the work, prices the next job and answers the phone, so the reminder goes out when someone remembers.
We build invoice chasing that runs from the accounting software you already use, such as Xero, QuickBooks or Sage. Reminders go out on the dates you set, in your wording, and stop when the invoice is paid. See how invoice chasing automation works, or browse more practical guides in our Knowledge Hub.
For interest that starts to run between 1 July and 31 December 2026, the statutory rate is 11.75% a year: 8% over the Bank of England base rate of 3.75% on 30 June 2026.
Simple. It is charged on the amount of the debt only, not on interest already added.
Yes. The fixed sum of £40, £70 or £100 is on top of the interest, and you can charge it once for each late payment.
No. The rate is fixed by the date the interest started to run, using the base rate on the reference date before it.
Book a free 30-minute call, or ring Dave on 01858 589789. We will look at how your invoices are raised and chased today and tell you what we would change.
Rates and rules checked on 12 October 2026. This page explains the law in general terms. It is not legal advice. For a disputed or large debt, speak to a solicitor.
