Late payment interest calculator
Based on the Late Payment of Commercial Debts (Interest) Act 1998 · Reviewed November 2026
Enter the amount, the due date and the payment date. The calculator gives the days late, the interest and the total. The UK statutory rate comes filled in and you can change it.
- Days late
- 45
- Interest
- GBP 34.77
- Fixed compensation
- GBP 70.00
- Total due
- GBP 2,504.77
Simple interest per day on 365 days. The rate you type is the rate used.
Your file never leaves your device.
How it is calculated
Interest = amount × yearly rate × days late ÷ 365.
The UK statutory rate is the Bank of England base rate plus 8%. The rate comes from the Late Payment of Commercial Debts (Rate of Interest) (No. 3) Order 2002.
Bank Rate has been 3.75% since 18 December 2025, read on bankofengland.co.uk on 31 October 2026. A debt that falls late between 1 July and 31 December 2026 carries 11.75% a year.
The Act adds a fixed sum per debt. It is £40 under £1,000, £70 up to £9,999.99 and £100 from £10,000.
Worked example
| Input or result | Value |
|---|---|
| Amount | £4,800.00 |
| Due date | 15 August 2026 |
| Payment date | 31 October 2026 |
| Yearly rate | 11.75% |
| Days late | 77 |
| Interest | £118.98 |
| Fixed sum | £70.00 |
| Total | £4,988.98 |
The calculator then writes the message. «Your balance as of today is £4,988.98, including £118.98 of interest and a £70 fixed sum.»
How to use it in four steps
- Type the unpaid amount of the invoice.
- Set the due date and leave the payment date as today.
- Keep the statutory rate or type the rate from your contract.
- Copy the message, send it by WhatsApp or download the PDF statement.
Field by field
| Field | What to enter |
|---|---|
| Amount | The unpaid amount, without earlier interest |
| Due date | The agreed date, or 30 days after delivery if none was agreed |
| Payment date | Today by default, or the day the money arrived |
| Yearly rate | Statutory rate pre-filled, editable for a contract rate |
Common mistakes
- Using it on a debt owed by a consumer. The 1998 Act covers businesses only.
- Counting from the invoice date instead of the due date.
- Using today's Bank Rate for a debt that fell late in an earlier half year.
- Adding interest to interest. Statutory interest is simple.
For GST interest in India, type the rate set by the GST law in the rate field. The formula is the same.
Let the reminder go out on its own
Makatea sends the WhatsApp or email reminder on the due date and on fixed days after. When the customer pays, Makatea records the payment and stops the reminders. Try it free for 14 days, no card needed.
Free on Makatea: free invoice generator
Frequently asked questions
What rate does the calculator use?
11.75% a year by default, which is Bank Rate of 3.75% plus 8%. You can type any other rate.
Does it add the fixed compensation?
Yes. It adds £40, £70 or £100 depending on the amount.
Can I use it for consumer debts?
No. The statutory rate and the fixed sum apply only between businesses.
Is the interest compound?
No. It is simple interest counted per day on a 365-day year.
Is my data saved anywhere?
No. Your data never leaves your device.
Is the result legal advice?
No. It applies the formula to your figures. A solicitor can confirm a dispute.
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Keep reading
Late Payment of Commercial Debts (Interest) Act 1998
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