Tax & ATO
Australian Company Number
An Australian Company Number (ACN) is a unique nine-digit identifier ASIC issues to every company registered under the Corporations Act 2001. It marks the company as a separate legal entity distinct from its owners. A company's ABN is simply its ACN with two extra check digits in front; sole traders and partnerships never have an ACN.
The ACN is issued automatically the moment a company is registered with ASIC, and it stays with the company for life, even through name changes. Its job is identification: company names can be similar or change over time, but the ACN pins down exactly which legal entity signed a contract, issued an invoice or owns an asset. That matters because a company is a separate legal person from its directors and shareholders; the ACN is how that person is identified in the Corporations Act 2001 world.
Companies must display the ACN (or the ABN, where its last nine digits match the ACN, which is almost always the case) on public documents: invoices, receipts, order forms, official company letterhead, cheques and documents lodged with ASIC. In practice most companies simply print their ABN, which satisfies the requirement. Alongside the number itself, directors of Australian companies must each hold a director identification number (director ID) issued through Australian Business Registry Services, a separate personal identifier introduced to combat phoenix activity. ASIC's guidance on the Australian Company Number on asic.gov.au covers the display rules in detail.
The three identifiers do different jobs, and every company holds all three.
| Identifier | Digits | Issued by | Who has one | What it is for |
|---|---|---|---|---|
| ACN | 9 | ASIC | Registered companies only | Identifies the company as a legal entity |
| ABN | 11 | Australian Business Register | Any entity carrying on an enterprise | Tax and invoicing identity, GST and PAYG registrations |
| TFN | 9 | ATO | Individuals and entities | Private identifier for tax returns and super |
A useful memory hook: the ABN of a company is its ACN wearing two extra digits. When ASIC registers a company with ACN 123 456 789 and the company then applies for an ABN, the ABR issues something like 53 123 456 789. Sole traders and partnerships skip the ACN entirely: they are not companies, so they identify themselves with an ABN for business dealings and a TFN for tax.
If you operate through a Pty Ltd, the ACN is part of the price of limited liability. The company must pay ASIC's annual review fee each year on the anniversary of registration, keep its registered office and officeholder details current, and pass an annual solvency resolution. Letting the review fee slide attracts late fees and, eventually, deregistration, at which point the company's assets can vest in ASIC. These obligations exist regardless of whether the company traded at all during the year.
For everyone else, the ACN is a due-diligence tool. Before signing a significant contract, check that the company name on the contract matches the entity behind the ACN, and that the company is registered and not in external administration; a free search of ASIC's registers or an ABN lookup on OneBookPlus shows the linked ABN, GST registration and status. Quoting the ACN or ABN on your own company invoices is not optional decoration: it is what makes the document identify a real legal entity, and it is one of the elements of a valid tax invoice when combined with the other ATO requirements.
The definitions above only get you so far; the free OneBookPlus ABN lookup tool turns them into your own figures in seconds, no sign-up needed.
No. ACNs are issued only to companies registered with ASIC. A sole trader is not a separate legal entity, so they operate under their own name (or a registered business name) with an ABN for invoicing and their personal TFN for tax.
On public documents such as invoices, receipts, order forms, official letterhead and documents lodged with ASIC. A company can show its ABN instead where the ABN's last nine digits are the ACN, which is why most companies simply print their ABN everywhere.
For a company, the ABN is built from the ACN: the Australian Business Register takes the nine-digit ACN and adds two leading check digits to form the 11-digit ABN. The ACN identifies the company with ASIC; the ABN identifies it to the ATO and on tax invoices.
Last reviewed and updated: by Bishal Shrestha