As of 13 August 2026, AI can only partly calculate statutory interest on a commercial debt.

What to actually do

1. Hand it to a person

   The route this page recommends

   Someone with a licence or accountable authority has to sign this before it counts.

2. Use a tool built for this

   Second choice

3. Do it yourself

   The distant third

   A chat interface, chat-fluent skill, and roughly 30 minutes until you can act on the result.

   How to actually do it

   1. Open the contract, relevant invoices, delivery or acceptance records, payment ledger and correspondence about disputes or agreed extensions.
   2. Make a single fact sheet containing the principal for each invoice, the contractual payment deadline, any agreed variation, every payment date and amount, and the proposed calculation end date.
   3. Open GOV.UK and official legislation sources and find the statutory interest regime and rate history that may apply to the transaction; save the source links and the dates on which each rate changed.
   4. Paste the fact sheet, relevant contract wording and verified rate information into a chatbot with the supplied prompt, and ask for a separate calculation for each invoice or principal balance.
   5. Recalculate each period in a spreadsheet using the model's principal, rate and day-count figures, then compare the spreadsheet total with the drafted schedule.
   6. Ask a solicitor to confirm the applicable statutory basis, start date, treatment of disputed or part-paid sums and the wording of any demand before you send or rely on the schedule in a serious dispute.

   Prompt

   Calculate the statutory interest on the commercial debt described below and produce a schedule that I can check.
   
   Facts:
   - Creditor: [business name]
   - Debtor: [business name]
   - Contract or legal basis: [paste the relevant clause or describe the transaction]
   - Invoice or principal amount: [amount and currency]
   - Invoice date: [date]
   - Contractual payment deadline: [date, or say none]
   - Date payment became overdue: [date, if known]
   - Payments received: [each amount and date]
   - Disputed amount or partial dispute: [details, or none]
   - Proposed calculation end date: [date]
   - Any contractual interest term: [paste it, or say none]
   - Any other facts that may affect interest: [details, or none]
   
   Use UK sources only. First identify which statutory interest regime could apply, such as the Late Payment of Commercial Debts legislation or another basis, and explain what facts make it applicable. Do not assume that statutory interest applies. Check the relevant rate and rate-change dates against current GOV.UK or official legislation sources, state the source and access date for each rate, and say if you cannot verify a rate. Do not invent missing facts or rates.
   
   Then calculate interest in a table showing each period, principal balance, rate, number of days, formula and interest amount. Explain how you treated VAT, partial payments, disputed sums, weekends, the end date and any contractual interest. Show the arithmetic in a way I can reproduce in a spreadsheet. Give a total principal, total interest and grand total, rounded only at the final stage. List every assumption and every point that needs a solicitor to confirm. This is not professional advice.

   Open it prefilled in ChatGPT or Claude, or copy it into Gemini, which takes no prefill link.