Late Payment Interest Calculator
An invoice is overdue. For commercial debts in the UK you can add statutory interest — the Bank of England base rate plus 8% a year — plus a fixed compensation sum per invoice. Put the numbers in and this works out what you're owed, and writes the line you can paste into the chaser. Everything stays in your browser.
How this works
Under the Late Payment of Commercial Debts (Interest) Act 1998, a business invoicing another business can charge interest on an overdue payment at the Bank of England base rate plus 8% a year. It runs from the day after payment was due until the day it is paid. This calculator applies that daily: amount × (base rate + 8%) ÷ 365 × days overdue.
On top of the interest you can claim a fixed sum for each late invoice, set by the size of the debt:
- £40 — debts under £1,000
- £70 — debts from £1,000 to £9,999.99
- £100 — debts of £10,000 or more
If chasing the debt actually cost you more than the fixed sum, you can claim the reasonable extra costs too — this calculator doesn't try to guess those.
This is a calculation, not legal advice. It assumes a commercial (business-to-business) debt with no different interest rate agreed in your contract — if your contract sets its own rate, that usually applies instead. It doesn't know your contract, your payment terms, or whether the debt is disputed, and it isn't a substitute for advice on recovering it. The Invoice Tracker keeps the whole ledger — what's out, what's overdue, and how long each client actually takes to pay.