Sole traders · Invoicing
Sole trader invoicing: a simple UK guide (2026/27)
21 August 2026 6 min read
What every invoice must include, how to number them, when to chase late payments, and how to avoid the most common invoicing mistakes that cost sole traders money.
A well-formed invoice gets paid faster. A badly-formed one bounces around your client's finance team for weeks. Here's the minimum UK invoice standard — plus the things that get you paid on time.
Legally required on every UK invoice
- The word "Invoice" and a unique sequential number (INV-001, INV-002…).
- Your business name and address (or trading name if different).
- The client's business name and address.
- Invoice date and the date the work was supplied.
- Description of goods or services.
- Amount charged (net, VAT if applicable, gross total).
- Your VAT number if VAT-registered (turnover over £90,000).
The bits that get you paid faster
- Payment terms up front: "Payment due within 14 days of invoice date." Not "when convenient".
- Bank details in the footer — sort code, account number, account name.
- A polite reference line: "Please quote invoice INV-042 in your bank transfer."
- Late payment interest clause: legally you can charge 8% + Bank of England base rate on late payments. Adding this line often prompts payment on time — you never have to actually chase.
Chasing late payments (without burning the relationship)
| Days late | Action |
|---|---|
| 0 (day of) | Polite reminder email — "Just checking you got INV-042?" |
| 3 | Slack/text nudge, casual tone. |
| 7 | Formal email, cc their finance contact. |
| 14 | Final notice mentioning statutory interest. |
| 21+ | Small claims court / debt recovery firm (usually just the letter is enough). |
Common mistakes that cost money
- Skipping the invoice number — you can't chase what you can't reference.
- Sending as a Word doc, not PDF — Word docs get edited by clients.
- Waiting a month to invoice — invoice the moment work completes; every day's delay is a day past your payment terms.
Clok generates a proper UK-formatted PDF invoice from your logged hours in one click, including sequential numbering and your bank details. Solo tier and above.
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