Invoice numbering
A unique sequential number makes invoices easy to trace and is one of the details required on a full VAT invoice. Use one or more sequences consistently.
What HMRC expects
A full VAT invoice must include a unique sequential number based on one or more series. Numbers can be numeric or alphanumeric, as long as the series runs consecutively. You can run separate sequences for different business units or customers if you keep them traceable.
Good invoice numbering schemes
- INV-2026-0001 — year plus sequence (simple and readable)
- DOC-0001, DOC-0002 — one sequence for all document types
- INV-UK-0001 / INV-US-0001 — separate sequences for different entities or markets
- QTE-0001 for quotes, INV-0001 for invoices — separate series per document type
What to do about gaps and cancelled invoices
If an invoice is cancelled or spoiled, keep a record and be able to explain the gap. Do not reuse a number for a different customer or supply. If you use accounting software, let it manage the sequence rather than editing numbers by hand.
Related tools and guides
Frequently asked questions
Can invoice numbers include letters?
Yes. HMRC allows numbers to be numeric or a combination of letters and numbers, as long as they form a unique, sequential series.
Can I have more than one invoice sequence?
Yes. HMRC accepts multiple sequences, including separate sequences for different business units or divisions, provided each is traceable.