How to Create an Invoice Number

An invoice number is a unique identifier you assign to each invoice so it can be tracked, referenced, and reconciled with payments. The ATO doesn't mandate a specific format, but your numbering must be sequential, unique, and consistent so no two invoices share the same number.

Common invoice numbering systems:

Pure sequential: 0001, 0002, 0003 — simple and easy to track
Prefixed sequential: INV-0001, INV-0002 — clear and professional
Year prefixed: 2026-001, 2026-002 — resets each financial or calendar year
Client coded: ACME-001, ACME-002 — handy if you only have a few clients
Date based: 20260526-01 — encodes the issue date in the number

Whichever format you pick, stick with it. Skipping numbers, reusing numbers, or jumping around makes bookkeeping and ATO audits painful. Most invoice generators including InvoiceSonic increment the number automatically so you don't have to remember the last one. Avoid leaving gaps in your sequence — the ATO can flag them as missing or deleted invoices.

How to Create an Invoice Number

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