Calculate statutory interest on unpaid debts and small claims with ClaimsPilot’s free UK interest calculator — quick, accurate, and no sign-up needed.
Free small claims interest calculator — powered by ClaimsPilot
When someone owes you money and refuses to pay, the financial impact rarely stops at the original debt. Every week that passes without payment is another week of lost income, disrupted cash flow, and growing frustration. What many people do not realise is that UK law entitles claimants to add statutory interest to the amount they are owed — and that interest can make a meaningful difference to the final sum recovered.
ClaimsPilot’s free interest calculator takes the guesswork out of this process. Whether you are a sole trader chasing an unpaid invoice, a landlord recovering an undisputed deposit, or an individual pursuing a consumer dispute, the tool gives you an accurate, defensible figure to include in your claim — in seconds.
This article explains how statutory interest works in the UK small claims context, how the ClaimsPilot calculator helps you get it right, and what steps to take once you have your figure.
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What is statutory interest and when can you claim it?
Statutory interest is the interest a creditor is legally entitled to charge on overdue debts. In the UK, the rate and legal basis depend on the type of debt involved.
For business-to-business (B2B) debts, the Late Payment of Commercial Debts (Interest) Act 1998 gives creditors the right to charge interest at 8% above the Bank of England base rate. This applies automatically to qualifying business contracts unless a different rate was agreed in writing. As of 2025, with the base rate sitting above 4%, the statutory rate for late commercial payments is over 12% per annum — a figure that adds up quickly on larger invoices.
For consumer and non-commercial claims, the position is slightly different. When a claim proceeds through the County Court, the court has discretion to award interest under Section 69 of the County Courts Act 1984. The conventional rate applied by the courts is 8% per annum on the judgment debt. Claimants cannot always demand this as of right before proceedings begin, but including a reasoned request for interest in a letter before action and then in the claim form is standard practice.
Understanding which category your debt falls into is essential before you calculate a figure. ClaimsPilot’s interest calculator prompts you to specify the nature of the debt so the correct rate is applied from the outset.
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How the ClaimsPilot interest calculator works
The ClaimsPilot interest calculator is designed to be straightforward, even if you have never made a formal claim before. There is no account required to use it, and the process takes under a minute.
Here is what you enter:
- The principal amount — the original debt, excluding any interest
- The start date — typically the date the payment became overdue (for invoices, this is usually the payment due date; for other debts, it may be the date of the event giving rise to the claim)
- The end date — either today’s date or the expected date of judgment
- The type of debt — commercial or non-commercial, which determines the applicable statutory rate
Once submitted, the calculator returns:
- The total interest accrued to date
- A daily interest figure, so you can see how the amount grows if the debtor continues to delay
- The combined total of principal plus interest — the sum you can legitimately claim
This combined figure is what you should include on your letter before action and, if necessary, on your County Court claim form.
The daily interest figure is particularly useful. Courts and debtors alike take claims more seriously when a claimant can demonstrate that delay has a quantifiable cost. Stating in correspondence that interest is accruing at, say, £2.74 per day focuses minds in a way that a flat demand sometimes does not.
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Why getting the interest figure right matters
Including the wrong interest figure — whether too high or miscalculated — can undermine an otherwise solid claim. If a claimant overclaims, a court may reduce the award or, in some circumstances, make adverse costs orders. If a claimant underclaims, they leave money on the table that they were lawfully entitled to recover.
There are a few common mistakes worth highlighting:
Using the wrong start date. For invoices with payment terms of 30 days, interest does not begin accruing on the invoice date — it begins the day after the payment deadline passes. For B2B debts under the Late Payment Act, this is clearly defined: interest starts 30 days after the invoice date or the date goods or services were delivered, whichever is later, unless different terms were agreed.
Applying the wrong rate. Some claimants apply 8% to a commercial debt when they should be using the Late Payment Act rate (8% above base). Others attempt to claim compound interest when statutory interest in small claims contexts is calculated on a simple basis only.
Failing to update the figure. A calculation done three months before filing a claim will be out of date by the time the claim is submitted. The ClaimsPilot calculator allows you to run the numbers again at any point, and the daily rate figure means you can update your total right up to the moment you file.
For guidance on how interest figures are treated within the formal claims process, the GOV.UK guide to making a court claim for money is a useful reference.
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Using your interest figure in a letter before action
Before issuing a formal claim through the courts, you are required — and strongly advised — to send a letter before action (also known as a letter before claim). This letter notifies the debtor of the amount owed, gives them a reasonable opportunity to pay or respond, and demonstrates to the court that you acted in good faith before litigating.
Including your interest figure in this letter serves two purposes. First, it shows the debtor the full financial exposure they face if they ignore you. Second, it establishes a documented record of when and how you calculated the interest, which may be relevant if the matter proceeds to a hearing.
ClaimsPilot’s letter before action generator is designed to work seamlessly alongside the interest calculator. Once you have your figure, you can use it directly in the generated letter — the tool formats the claim professionally, includes the statutory interest breakdown, and sets out the deadline for response in line with pre-action protocol guidance.
For most small claims, a well-drafted letter before action resolves the dispute without the need for court proceedings. Debtors who see a creditor has done their homework — correct figures, correct law, correct procedure — often choose to settle rather than face a hearing.
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When to escalate to a formal small claims court filing
If the letter before action goes unanswered or is rejected, the next step is to issue a claim through the Money Claim Online (MCOL) service or, for claims under £10,000, via the small claims track of the County Court. In England and Wales, the small claims limit is currently £10,000 for most claim types.
When filing, you will be asked to specify the amount claimed and the basis on which interest is sought. The interest figure from the ClaimsPilot calculator, combined with the statutory basis (either the Late Payment Act or Section 69 of the County Courts Act), gives you everything you need to complete this section accurately.
It is also worth noting that court fees are calculated on the total amount claimed, including interest. Using an accurate calculator ensures you pay the correct fee — neither overpaying nor understating your claim.
The GOV.UK small claims guidance also covers what happens after a judgment is entered, including enforcement options if the debtor still refuses to pay.
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Start calculating now
Recovering what you are owed is rarely straightforward, but having accurate figures from the out