Recordkeeping guide
Invoice Numbering
Use a unique, consistent identifier for every issued invoice. A simple sequence such as INV-0001 is easy to reconcile; prefixes or year codes can be added when they have a documented purpose. Do not reuse a number for a different transaction.
Reviewed 2026-07-29 · General information, not legal, tax or accounting advice.
| Pattern | Good use | Caution |
|---|---|---|
| INV-0042 | Simple continuous sequence | Choose enough padding for growth |
| 2026-0042 | Year plus sequence | Document whether the sequence resets |
| EU-INV-0042 | Separate controlled business series | Avoid unnecessary complexity |
| CLIENT-0042 | Rarely needed | Can expose customer information |
Make every number stable and traceable
The number identifies the document; status belongs in a separate field. Keep the same number when an invoice moves from draft to sent to paid. Use a credit note or permitted correction process when an issued invoice changes.
Record voided or cancelled numbers instead of silently reusing them when an unbroken audit trail is required. Tax regimes may impose more specific sequencing rules.
Prevent duplicates
Use one source of truth for the next number, especially when several people issue invoices. This browser tool formats a number but does not coordinate a server-side sequence, so check your invoice register before issue.
A prefix can separate legal entities, branches or permitted series. Do not create several overlapping sequences merely for aesthetics.
Example policy
Northstar Studio uses INV-0001 upward without monthly resets. Drafts can be deleted before issue; sent invoices keep their number. A cancelled issued invoice remains in the register as void, and a new invoice receives the next number.
Use the next tool
Continue through the invoice lifecycle
Primary sources
- EU VAT invoice information — European Commission
- UK invoice requirements — GOV.UK