A desk at 10pm, a printed invoice and a form side by side with a pen.

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How do I write the particulars of claim for an unpaid invoice?

The short answer

Facts, in date order. Particulars of claim are a concise statement of the facts1 your claim rests on: who the parties are, the agreement, the invoice and that it was not paid. If you claim interest on a set amount, such as an unpaid invoice, the same rule lists five things the claim must say1: the rate, the date it runs from, the date it is worked to, the total to that date and the daily rate after it. So the daily figure from your interest working goes into the claim itself.

Mara, WolfX research desk
Written with AI, checked by a person · 8 October 2026

England and Wales only. WolfX is software, not a law firm.

What you can add

A £6,400 website build, claim issued 9 October 2026

Say you invoiced another business £6,400 on 5 May 2026, due on 4 June 2026. Your letter before action went out on 14 September and was ignored. Interest started on 5 June 2026, so the rate is 11.75%10: Bank Rate on 31 December 202511 was 3.75%, plus 8%. You issue the claim on 9 October 2026, which is 127 days late.

£6,400.00The invoice

£261.65Interest: £6,400 × 11.75% ÷ 365 × 127 days7

£70.00Fixed sum (invoices from £1,000 to £9,999.99)9

£6,731.65Claimed on 9 October 2026

The particulars carry £6,400.00, interest of £261.65 to 9 October 2026, £2.06 a day after that, and £70.00.

The road ahead

Five steps. One court fee.

Step 1: Gather the facts
Pull out the contract or emails, the invoice, your letter before action and your interest working. Everything in the particulars comes from these.
Facts only. Leave out the history of the relationship and the tone of the emails.
Cost: FreeTime: 15 minutes
Step 2: Work the interest to the day you issue
Choose the day you will issue the claim and work the interest to that day. Rule 16.41 asks for the rate, the start date, the date worked to (no later than the issue date), the total so far and the daily rate after it.
Claim one kind of interest. If your contract sets its own rate7, you cannot also claim statutory interest under section 18; what else you can claim sets out the choice.
Cost: FreeTime: 10 minutes
Step 3: Describe the agreement the way it was made
Written: attach the contract or terms2, or serve them with the particulars. Spoken: set out the words used, by whom, to whom, when and where. By conduct: say what was done, by whom, when and where.
If the terms sit in emails or a quote, treat the deal as written and attach them.
Cost: FreeTime: 10 minutes
Step 4: Fill in the model and sign the statement of truth
Use the model below. Keep the order the facts happened in, and say how the due date was fixed, because the interest runs from it.
The particulars end with a statement of truth. For a company it is signed by a director, secretary or manager3, who prints their full name, states their position and dates it.
Cost: FreeTime: 20 minutes
Step 5: Put it in the claim and pay the fee
Claim online6. The particulars go in the claim form or are served within 14 days after the claim form is4. The fee on £6,731.65 is £45512, on the claim plus interest.
Expect a defence 14 days after the particulars are served5, or 28 days if they file an acknowledgment of service.
Cost: £455 court feeTime: Same day

A letter you can copy

Model particulars of claim

Use it when the letter before action has gone unanswered and you are filling in the particulars box on the claim form.

New email

SubjectParticulars of claim: unpaid invoice

IN THE COUNTY COURT (Claimant) and (Defendant) PARTICULARS OF CLAIM 1. The Claimant is , a company registered in England and Wales. The Defendant is , a company registered in England and Wales. Each acted in the course of a business. 2. 3. 4. The Claimant issued invoice . The invoice fell due on . 5. On the Claimant sent the Defendant a letter before action asking for payment. The invoice remains unpaid. 6. The Claimant claims interest under section 1 of the Late Payment of Commercial Debts (Interest) Act 1998 at a year from to , the date of issue of the claim form. The interest to that date is . Interest continues to accrue after that date at a day. 7. The Claimant also claims the fixed sum of under section 5A of that Act. 8. The Claimant claims the invoice amount, the interest in paragraph 6 and the fixed sum in paragraph 7. STATEMENT OF TRUTH The Claimant believes that the facts stated in these particulars of claim are true. The Claimant understands that proceedings for contempt of court may be brought against anyone who makes, or causes to be made, a false statement in a document verified by a statement of truth without an honest belief in its truth. Signed: Full name and position: Date:

Tap a highlighted gap to see what goes in it.

Change any paragraph that is not true for you. If part of the invoice was paid, say how much and when. Then paste it into the particulars box if it fits, or attach it to a paper claim form. Money Claim Online's box holds 1,080 characters and cuts off the rest. There, tick the box for detailed particulars and type a short summary. Within 14 days of issue, post this with a letter quoting the claim number, and file form N215. If the deal is written, attach the contract or terms. The signer prints their name and writes the date they sign. Keep a dated copy of what you sign.

When not to bother

When it isn't worth it

The invoice is genuinely disputed. If they say the work was poor, the particulars turn into a fight over the facts. Settle or answer the dispute first, and claim the undisputed part.
The company is in administration or liquidation. A court claim is usually the wrong tool, because the money is shared out through the insolvency instead. Find out which it is before you pay a fee.
The claim is small. The fee on a claim of £500.01 to £1,000 is £7012. It is added to your claim, but you see it again only if they pay. Weigh that against the client.
They have no address in England or Wales. You cannot claim online6 then, and Scotland and Northern Ireland have their own rules.

The Wolf's note

The box asks for facts, and you already hold them: a contract, an invoice, a date, a letter. Put them in the order they happened, give the interest its five numbers and leave the story out. A claim that reads like a ledger is hard to argue with.

Mr. Wolf · the AI inside WolfX

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