Work out what you may legally add to an overdue B2B invoice: statutory interest at the locked half-year rate, plus the automatic fixed compensation almost every invoice forgets.
| Statutory rate | — |
|---|---|
| Reference rate used | — |
| Interest per day | — |
| Interest so far | — |
| Fixed compensation | — |
| Total you can invoice | — |
| Lost if you skip it | — |
This page is the working piece. The full pack has everything below.
Work out what you may legally add to an overdue B2B invoice: statutory interest at the locked half-year rate, plus the automatic fixed compensation almost every invoice forgets.
A solicitor's letter before action runs about GBP 150-400; a commercial collection agency takes 8-15% of whatever it recovers.
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Real numbers from this tool, line by line.
If a business customer has not paid you, two numbers are already yours by law, and you do not need a clause in your contract to claim either of them. Most people charge neither, because both of them are easy to get wrong in a way that looks right.
In the UK, statutory interest on a late commercial debt is the Bank of England base rate plus eight percentage points, under the Late Payment of Commercial Debts (Interest) Act 1998. The trap is the word *base rate*. It is not the base rate today. It is the base rate in force on the previous 31 December or 30 June, and it stays locked for that whole half-year even if the Bank moves rates in the middle of it.
So for a debt that fell late in the second half of 2026 the reference rate is the one that stood on 30 June 2026: 3.75%. Statutory interest is 11.75% a year. Ask a chatbot and it will quote you whatever base rate it happened to learn, with total confidence and no mention of the lock.
On top of the interest you may add a fixed compensation sum, automatically, per invoice:
In the euro area the equivalent is a flat €40 under Article 6 of Directive 2011/7/EU. This is not a penalty you have to argue for. It is owed the moment the debt is late.
The Directive sets eight percentage points as a *minimum*, and general-purpose calculators tend to apply eight everywhere. Germany implemented nine: section 288(2) BGB gives the Basiszinssatz plus nine percentage points on business-to-business debts. On 1 July 2026 the Basiszinssatz went to 1.52%, so the German B2B rate is 10.52%, not the 10.40% you get from the euro-area default.
One more note for 2026: the Regulation that was proposed in 2023 to replace the Directive, the one with the hard 30-day payment cap, was blocked in Council and never took effect. Directive 2011/7/EU is still the law. Plenty of advice written in 2024 says otherwise.
Take £8,400, 74 days past its due date, UK, second half of 2026:
Reference rate 3.75% locked for 2026-H2
Statutory rate 11.75% a year
Interest per day £2.70
Interest so far £200.10
Fixed compensation £70.00
Total you can invoice £8,670.10Charge the interest and forget the fixed sum and you have handed back £70 on one invoice. Do that across a year of late payers and it is not a rounding error.
Late Payment Interest Claim is a browser extension for Chrome, Edge and Firefox. It sits next to the invoice you are already looking at, and works out the locked reference rate, the interest to date, the fixed compensation tier and the total you may invoice, for the UK, the euro area and Germany. Ten statutory rules are encoded as a table in the source, each one carrying its citation, so you can check the figure rather than trust it.
The calculation is free and complete: no key, no cap, no watermark, for as many invoices as you have. The full version, $60 once, adds one thing on a different axis: it downloads the worked claim as a .csv row you keep, hand to your accountant, or attach to a letter before action. A solicitor's letter before action generally runs about £150 to £400, and a collection agency takes 8 to 15% of whatever it recovers. 7-day full refund.
It works out the statutory interest and the fixed compensation you may legally add to an overdue business-to-business invoice in the UK, the euro area or Germany. You enter the sum owed, any part payment and the days past the due date, and it returns the rate applied, the interest to date, the fixed sum and the total you can invoice.
Freelancers, agencies and small suppliers who have invoiced a business customer that has not paid. It assumes a business-to-business debt, which is the only kind the late payment statutes cover. Consumer debts and salaries work differently and are outside what this calculates.
The statute does not use today's central bank rate. It locks the rate to the one in force on 31 December or 30 June before the invoice fell late, and holds it for the whole half-year. A chatbot quotes whatever rate it learned. Most free calculators also apply eight points in Germany, where section 288(2) BGB gives nine, and skip the fixed sum entirely.
The calculation is free and complete: every rate, the interest, the fixed compensation and the total, for any number of invoices, with no key and no limit. The full version at 29 dollars adds one thing on a different axis, keeping it: the worked claim downloads as a .csv row for your records or your accountant.
A solicitor's letter before action generally runs about 150 to 400 pounds, and a commercial collection agency takes between 8 and 15 percent of whatever it recovers. The fixed compensation alone is 40 to 100 pounds per invoice, and it is money you are entitled to that a hand-typed reminder simply leaves behind.
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