Key takeaway
Confirm the debt and applicable rate basis before calculating interest. A charge on paper is separate from cash collected, and a proposed reform is separate from current law.
Today’s base rate may be the wrong input
A controller preparing a late-payment calculation needs more than an overdue balance and a current rate headline. The relevant debt, contractual position, due date and overdue period must be established first. The selected reference rate and any part-payment or credit can then change the arithmetic. A calculator cannot supply the missing legal and factual premises.
UK government guidance describes statutory interest for business-to-business late payment as eight percentage points plus the Bank of England rate, with a contract-rate qualification. The Office of the Small Business Commissioner identifies the December 31 and June 30 reference dates for the following half-year. Do not replace that reference-period question with whichever live rate appears on the day you open a spreadsheet.
This is an educational UK commercial-debt example checked on 16 October 2026. It does not determine that a particular data license qualifies, that an invoice is overdue or that a contractual remedy is legally ineffective. The government’s older user guide discusses substantial-remedy questions in more detail than its short current page; a real clause needs qualified review rather than a shortcut from either summary.
Work one principal and one period
Hypothetical example: stipulate an eligible GBP 10,000 principal, thirty confirmed overdue days within one applicable reference period and no part-payments or credits. Assume the applicable reference base is 4% and the contract does not displace this calculation. The 4% is a teaching input, not a statement of the current or historical rate for an actual invoice.
The assumed annual rate is 4% + 8 percentage points = 12%. Simple interest is GBP 10,000 × 0.12 × 30/365 = GBP 98.630136…, shown as GBP 98.63. This illustration retains precision until the final money amount. It does not compound the debt or apply a rounded daily amount thirty times.
Government guidance lists a one-time recovery sum of GBP 100 for a qualifying debt of GBP 10,000 or more. Under these stipulated eligibility facts, the added interest and compensation total GBP 198.63. That produces a hypothetical stated total of GBP 10,198.63, not proof that the debtor owes or will pay this amount.
The principal already contains the assumed qualifying debt. Do not add the original invoice again as a second loss, charge compensation for every reminder or calculate more interest on the illustrative interest invoice. A changed balance or interval requires a new calculation under the applicable rules.
Keep the 2026 bill in its proper status
The Commercial Payments Bill overview describes proposed mandatory interest and other reforms. When checked for this article on 16 October, Parliament’s bill news reported the September 15 report stage and scheduled third reading for October 20. Those observations do not establish enactment or commencement.
A press release about stronger future rules cannot justify presenting them as an existing entitlement. Preserve the observation date and recheck legislative status and any commencement provisions before relying on a new rule. This article’s worked calculation uses the separately identified existing guidance, not the proposed mandatory-interest measure.
The older 2014 government guide is useful for the simple-interest formula and reference-date explanation, but its age is material. Its description of the directive and former policy arrangements is not treated as a complete 2026 statement. The current guidance and bill pages were read separately; none is a transaction-specific legal opinion.
Give the calculation a checkable basis
For the actual review, keep the contract interest provision, invoice and accepted debt amount, evidence of the due date, credits or receipts, selected period and reference-rate evidence together. Ask the responsible adviser to resolve eligibility and contractual remedies. Keep the calculation editable so a corrected principal or date flows through to the final amount.
The worked GBP 198.63 is a charge calculation, not available cash or a probability of recovery. No original preparation, legal collection spending or tax treatment has been valued. This example starts with an existing debt; if an inquiry never produces a qualifying license debt, it creates no interest or recovery sum under this model. Any sunk preparation remains the company’s separate cost.
A controller can now explain each entered number without claiming a collection outcome: GBP 10,000 stipulated principal, 12% assumed annual rate, thirty days, GBP 98.63 interest and one GBP 100 sum. Keep the charge calculation, additional collection spending and bank receipt separate as the actual matter proceeds. One summed debt amount cannot establish all three.