An Australian Company Number (ACN) is a 9-digit unique identifier issued by the Australian Securities and Investments Commission (ASIC) to every company registered in Australia under the Corporations Act 2001. It identifies the company as a distinct legal entity, separate from its shareholders and directors.
When and where to display the ACN
Companies are legally required to display their ACN on all public documents and negotiable instruments, including invoices, tax invoices, letterheads, receipts, order forms, business cheques, and the common seal (if one is used). Failure to comply is an offence under the Corporations Act.
Correct invoice header
Acme Pty Ltd ABN 51 123 456 789 ACN 123 456 789 — both numbers appear side by side on the invoice.
ACN vs ABN
- Only companies have ACNs. Sole traders, partnerships and trusts do not.
- A company's ABN is typically the 9-digit ACN with a 2-digit check prefix, giving an 11-digit ABN.
- If a company's ABN is displayed on an invoice, the ACN does not also need to appear — the ABN is sufficient to satisfy the requirement, because the ACN can be derived from it.
Finding and verifying an ACN
ACNs are publicly searchable through ASIC Connect (asic.gov.au). Accountants can verify a company's registration status, registered office, directors, and lodgement history. You can also cross-check an ACN via ABN Lookup, which will show the associated ABN and GST registration details.
Common mistakes
- Displaying the ABN but omitting the ACN when both are required — technically, showing the ABN alone on a document satisfies the ACN disclosure requirement, but only if the company name is also shown.
- Confusing the ACN with the ARBN (Australian Registered Body Number), which is issued to foreign companies and some other registered bodies.
- Entering an ACN incorrectly on BAS forms — always verify against ASIC Connect.
What is an ARSN and how does it differ from an ACN?
An ARSN (Australian Registered Scheme Number) is a 9-digit number issued to managed investment schemes registered with ASIC — not companies. The format is the same as an ACN but the entities are different.
Does a company need a new ACN if it changes its name?
No. The ACN stays with the company for its entire existence, regardless of name changes. The new name is registered with ASIC and the same ACN continues.