An ACN is the 9-digit Australian Company Number ASIC gives every company when it's registered. An ABN is the 11-digit Australian Business Number that identifies any type of business, including sole traders and partnerships, and it's issued through the Australian Business Register managed by the ATO. Most companies have both.
If you're a sole trader, you only need to think about the ABN. The ACN only exists once you register a company. This guide sets out the difference using ASIC's and business.gov.au's pages as they read in October 2026.
ABN and ACN side by side
| ACN | ABN | |
|---|---|---|
| Full name | Australian Company Number | Australian Business Number |
| Length | 9 digits | 11 digits |
| Who issues it | ASIC | The Australian Business Register, managed by the ATO |
| Who gets one | Companies only, automatically on registration | Any business or enterprise that's entitled to one, including sole traders, partnerships and companies |
| Cost | Comes with company registration | Free to register |
| What it's for | Identifying the company on legal documents | Identifying the business to government, other businesses and the public |
Why the two numbers often look almost the same
This is the detail most people miss. ASIC says a company's ABN is often the same as its ACN with 2 extra numbers at the beginning. When that's the case, the company can show its ABN anywhere it would normally have to show its ACN. One number on your invoices then does both jobs.
If your ABN isn't built from your ACN, for example because the ABN came first under a different structure, you can't swap them, and the ACN has to go on the documents that require it.
Where your ACN has to appear
Under section 153 of the Corporations Act 2001, ASIC says companies must show their full name and their ACN (or a matching ABN) on:
- documents that must be signed, issued or published under the law
- documents signed or issued by or for the company for a particular transaction or dealing
- cheques, promissory notes and bills of exchange
The name and number must appear on the first page. Where several companies are listed on one document, each company's ACN goes next to its own name. You can label it "Australian Company Number", "ACN" or "A.C.N.", and the ABN as "Australian Business Number", "ABN" or "A.B.N." The number has to be clear and readable, and it must be obvious which company it belongs to. A company that uses a common seal must include its name, the words "Australian Company Number" and the ACN on the seal.
Getting each number
- Decide your structure. A sole trader or partnership only needs an ABN. A company gets an ACN on registration and usually applies for an ABN too.
- To get an ACN, register the company with ASIC. If you don't choose a name, ASIC uses the ACN itself as the company name, for example ACN 123 456 789 Pty Ltd.
- To get an ABN, apply through the Australian Business Register. You need to be running a business or other enterprise to be entitled to one.
- If your application has everything needed, you'll find out your ABN as soon as you finish the online form. Applications that need review can take 20 business days.
- Update your ABN details within 28 days of becoming aware of a change.
My step-by-step guide on how to apply for an ABN covers the application itself, and if you're not sure you qualify, start with do I need an ABN.
If your ABN application isn't approved straight away
Not every application gets an instant answer. Business.gov.au says an unsuccessful application gets a refusal number and a letter within 14 days explaining why, and an application that needs more review gets a reference number instead. Those reviews can take 20 business days, and the ATO may contact you for more information, so apply before you need to send your first invoice.
What each number does for you
Business.gov.au lists the practical benefits of an ABN: it verifies your business to others when ordering and invoicing, and it helps you avoid pay as you go tax being withheld from payments you receive. It doesn't replace your tax file number. The ACN's job is narrower: it's the company's legal identifier on the register and on formal documents, and it comes with company obligations such as the annual company review fee. If you change your business structure, for example from sole trader to company, you may need a new ABN.
To check another business's numbers, my guide to ABN Lookup shows how, and ASIC's company register search covers ACNs.
My verdict
If you trade as a sole trader, ignore the ACN and get your ABN, which is free. If you run a company, you'll have both, and the simplest setup is an ABN built from your ACN, so a single number satisfies ASIC's display rules on your invoices, contracts and website terms. Check your documents once against the section 153 list and you're done.
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Frequently asked questions
What is the difference between an ABN and an ACN?
An ACN is a 9-digit number ASIC issues to every company on registration. An ABN is an 11-digit number that identifies any type of business, issued through the Australian Business Register managed by the ATO.
Do I need both an ABN and an ACN?
A company gets an ACN when it's registered and most companies also have an ABN. Sole traders and partnerships only need an ABN, because ACNs are for companies.
Can I use my ABN instead of my ACN on invoices?
Yes, if your ABN is the same as your ACN with 2 extra numbers at the beginning. If it isn't, the ACN must appear where the law requires it.
How much does an ABN cost?
Nothing. Business.gov.au says it's free to register for an ABN through the Australian Business Register.
How many digits is an ACN?
An ACN has 9 digits. An ABN has 11 digits.
Does a sole trader need an ACN?
No. ACNs are issued only to companies when they're registered with ASIC. A sole trader uses an ABN.
Who issues the ABN?
The ABN is issued through the Australian Business Register, which the ATO manages, not by ASIC.
What happens if I don't choose a company name?
ASIC uses the ACN as the company name together with its legal status, for example ACN 123 456 789 Pty Ltd.
