ABN vs ACN: What's the Difference and Which You Need
ABN vs ACN: the short answer
An ABN (Australian Business Number) is an 11-digit number that identifies any business, from a sole trader to a large company, and it is issued through the Australian Business Register. An ACN (Australian Company Number) is a 9-digit number that identifies a company specifically, and ASIC issues it when the company is registered. If you run your business as a sole trader, you need an ABN and you will not have an ACN. If you register a company, you get both.
That single distinction, entity type, is what the two numbers are really about. Everything else follows from it: who issues the number, how long it is, and where it has to appear. This guide walks through each number, shows how a company's ABN is built from its ACN, and helps you work out which you need.
What is an ABN?
An ABN is your business's identifier for dealings with the Australian Taxation Office and with other businesses. Every business structure can hold one: a sole trader, a partnership, a trust, and a company are all entitled to an ABN. You apply for it free of charge through the Australian Business Register, which the ATO runs, so be wary of any third-party service that charges a fee to "get your ABN" for you.
The ABN does a lot of practical work once you have it. You quote it on invoices so customers do not withhold tax from your payments, you use it to register for GST and pay-as-you-go, and it is the number that appears on the public ABN Lookup register that anyone can search. An ABN is not a company and does not create a company. A sole trader with an ABN is still an individual running a business, personally liable for its debts.
What is an ACN?
An ACN is narrower. It exists only for companies, and ASIC issues one to every company at the moment it is registered under the Corporations Act. In ASIC's own words, "an ACN is a unique 9-digit number that identifies a company." A sole trader, partnership, or trust that has not incorporated has no ACN, because there is no company to identify.
The ACN marks the company as a separate legal entity, distinct from the people who own or run it. That legal separation is the reason a company exists in the first place, and it is why the ACN is tied to ASIC (the corporate regulator) rather than the ATO. Registering a company is a bigger step than getting an ABN: it costs more, carries ongoing ASIC obligations, and gives the company its own tax file number separate from any director's individual TFN.
How the two numbers connect
The definition-first explainers tend to skip how the two numbers relate. For a company, the ABN and ACN are not two unrelated strings. A company must have its ACN first, then applies for an ABN, and the ABR builds that ABN directly from the ACN: it takes the nine ACN digits and adds two check digits at the front.
So a company with ACN 123 456 789 will have an ABN made of those exact nine digits with two extra digits in front, of the form NN 123 456 789. The last nine digits of a company's ABN are its ACN. That is why ASIC lets a company show its ABN in place of its ACN on documents, as long as the ABN is the ACN with two numbers added at the start. One number is embedded in the other.
Sole traders have no such link, because there is no ACN to embed. A sole trader's ABN is issued against their individual tax file number, not an ACN.
ABN vs ACN at a glance
| ABN | ACN | |
|---|---|---|
| Full name | Australian Business Number | Australian Company Number |
| Length | 11 digits | 9 digits |
| Issued by | Australian Business Register (ATO) | ASIC |
| Who has one | Any business: sole trader, partnership, trust, company | Companies only |
| Purpose | Identify a business for tax and invoicing | Identify a company as a legal entity |
| Cost to obtain | Free | Company registration fee applies |
| Public register | ABN Lookup | ASIC company register |
Which one does your business need?
Start from your structure, because the structure decides the numbers.
If you are a sole trader, a partnership, or a trust, you need an ABN and nothing more on the company front. You will not have an ACN, because you have not created a company. This covers most freelancers, contractors, and small operators. Your individual TFN handles your tax, and if you turn over enough to register for GST, you do that against your ABN.
If you run a company, you have both, and they arrive in a fixed order. ASIC issues the ACN when you register the company; then you apply for the company's ABN, which is built from that ACN. You will use the ABN for day-to-day tax and invoicing and the ACN for company-law matters, though in practice the ABN covers most documents because it contains the ACN.
The decision between operating as a sole trader and registering a company is a separate question about liability, tax, and cost, not about which number is "better." An ACN is a consequence of choosing to incorporate, not a goal in itself.
Why the ABN matters for getting paid
The ABN is not just an identifier; leaving it off an invoice costs money. Under the ATO's no-ABN withholding rule, when a supplier does not quote an ABN for a supply and the payment is more than $75 (excluding GST), the paying business must withhold 47% of the invoice amount and send it to the ATO. The supplier gets 53% now and has to wait until tax time to recover the rest. A payer who fails to withhold when they should can face a penalty equal to the amount they should have held back.
There is a narrow exception. If the supply is a private or domestic one, or part of a hobby, the supplier can give the payer a completed "Statement by a supplier" form instead of an ABN, and no withholding applies. For anyone running a business, the practical answer is simpler: quote your ABN on every invoice.
The ABN is also the gateway to GST. You must be registered for GST once your business turnover reaches the $75,000 threshold, and you cannot register for GST without an ABN first. If GST applies to you, tracking the GST on every purchase becomes part of the job, which is where organised expense records start to matter for your BAS.
Where each number has to appear
A company's full name and its ACN must appear on the first page of the documents where they are required, such as letters and invoices. Because the ABN contains the ACN, ASIC allows the company to show its ABN instead of the ACN on those documents. A sole trader has no ACN to display, but should still quote their ABN on invoices for the withholding reason above.
When you receive an invoice from a supplier, the ABN on it is worth checking. You can look up any ABN on the public ABN Lookup register to confirm the business is real, registered, and entitled to charge GST. Keeping that supplier detail attached to each expense is part of good record keeping for the ATO.
Common misconceptions
"Having an ABN means I have a company." It does not. An ABN identifies a business of any kind. A sole trader with an ABN is still an individual, personally liable for the business, with no separate legal entity and no ACN.
"As a sole trader I should get an ACN too." There is nothing to get. An ACN only exists once you register a company with ASIC. If you have not incorporated, you cannot have an ACN, and you do not need one to invoice, register for GST, or claim sole trader deductions.
"The ABN and ACN are separate random numbers." For a company they are deliberately linked. The nine ACN digits sit inside the 11-digit ABN, with two check digits added at the front, which is exactly why ASIC lets one substitute for the other on documents.
How SparkReceipt helps with supplier ABNs
Whichever numbers your business holds, the day-to-day work is capturing the supplier details on every bill you pay, including the ABN, the GST, and the total. SparkReceipt reads that information off a photographed or emailed invoice automatically and files it as a categorised, GST-aware expense, so your records already carry the supplier's ABN and tax breakdown when you prepare a BAS or hand your books to an accountant. It reads receipts and invoices from any country and applies the right tax treatment, which is useful when some of your suppliers are overseas and quote no ABN at all. See pricing for the plan details, including the accountant seat.
Frequently asked questions
Can I have an ACN without an ABN? A company is issued its ACN by ASIC at registration and can technically exist before it applies for an ABN. In practice a trading company needs both, and applies for the ABN straight after registration.
Is a company's ABN just its ACN with extra numbers? Yes. The last nine digits of a company's ABN are its ACN, and the ABR adds two check digits at the front. That structure is why ASIC allows the ABN to be shown in place of the ACN on company documents.
Do I need an ACN to invoice clients as a freelancer? No. As a sole trader you invoice using your ABN. You do not have an ACN and do not need one. Quoting your ABN is what stops clients from withholding 47% of your payment.
How much does an ABN or ACN cost? Applying for an ABN through the Australian Business Register is free. An ACN comes with company registration, which carries an ASIC fee, so the ACN effectively costs whatever the current company registration fee is.
How do I check a supplier's ABN? Search the number on the public ABN Lookup register. It confirms whether the ABN is active, the entity type behind it, and whether the business is registered for GST.
Key takeaways
- An ABN identifies any business and is issued through the ATO's Australian Business Register; an ACN identifies a company specifically and is issued by ASIC.
- Sole traders, partnerships, and trusts have an ABN only. They do not have an ACN, because no company exists.
- A company has both, and the two are linked: its 11-digit ABN is its 9-digit ACN with two check digits added at the front.
- Leaving your ABN off an invoice can trigger 47% no-ABN withholding on payments over $75 excluding GST, so quote it every time.
- You need an ABN before you can register for GST, which becomes compulsory at $75,000 of turnover.