ABN and ACN are two of the most commonly confused identifiers in Australian business registration. They look similar, they’re often mentioned together, and many new business owners aren’t sure which one they have, which they need, or what to put on an invoice.
This guide explains both numbers clearly — what they are, who issues them, who needs them, and how they relate to each other.
The Short Answer
An ABN (Australian Business Number) is an 11-digit identifier issued by the ATO to all businesses — sole traders, partnerships, companies, and trusts. It is used for tax, GST, invoicing, and dealings with the ATO and other businesses.
An ACN (Australian Company Number) is a 9-digit identifier issued by ASIC only to registered companies. It confirms that the entity is a separate legal entity under the Corporations Act 2001 and is used for company law and ASIC compliance purposes.
Every company has both an ABN and an ACN. Sole traders, partnerships, and trusts only have an ABN — they cannot have an ACN because they are not registered companies.
ABN vs ACN: Side-by-Side Comparison
| Feature | ABN | ACN |
| Digits | 11 | 9 |
| Issued by | ATO (via Australian Business Register) | ASIC (upon company registration) |
| Who needs it | All businesses — sole traders, partnerships, companies, trusts | Companies only (Pty Ltd, Ltd, etc.) |
| Cost | Free | Free (included in ASIC company registration fee) |
| Purpose | Tax identification, GST, invoicing, dealings with ATO and suppliers | Legal company identification, ASIC compliance, public register |
| Creates legal entity? | No | Yes — confirms company is a separate legal entity |
| Displayed on | Tax invoices, quotes, BAS, ATO correspondence | Company documents, contracts, ASIC filings, letterhead |
| Can it change? | Can be cancelled or reissued; can be updated | Permanent — stays the same for the life of the company |
| Relationship | Independent (for sole traders, partnerships, trusts) | Company ABN usually incorporates the ACN with a 2-digit prefix |
What Is an ABN?
An Australian Business Number is a unique 11-digit identifier issued by the Australian Taxation Office through the Australian Business Register (ABR). It identifies your business to the government, to other businesses, and to the public — regardless of your business structure.
Every type of business entity in Australia uses an ABN:
- Sole traders — your ABN identifies you as a business operator for tax purposes
- Partnerships — the partnership has its own ABN, separate from each partner’s individual ABN
- Companies — the company has an ABN, which in most cases incorporates the company’s ACN with a 2-digit prefix added at the front
- Trusts — the trust has its own ABN, used for tax and business dealings, even though it has no ACN
Your ABN must appear on every tax invoice you issue. If you do not include your ABN on an invoice, the payer is legally required to withhold 47% of the payment and remit it to the ATO — a significant cash flow consequence for missing a number on a document.
An ABN is also required to register for GST (mandatory once turnover reaches $75,000), to register for PAYG withholding if you have employees, and to register a business name with ASIC.
Applying for an ABN is free and takes around 15 minutes online through the Australian Business Register at abr.gov.au. Most applications are processed instantly.
What Is an ACN?
An Australian Company Number is a unique 9-digit identifier issued by ASIC to every company registered under the Corporations Act 2001. As ASIC confirms, ASIC issues every company with an ACN when it is registered. The ACN confirms the company’s existence as a separate legal entity and is used by ASIC to monitor the company’s activities and compliance.
Only registered companies have ACNs. Sole traders, partnerships, and trusts do not receive an ACN because they are not registered as companies under the Corporations Act.
The ACN must appear on specific company documents including:
- All public documents the company issues — invoices, letterhead, contracts, purchase orders
- ASIC lodgements and annual review statements
- Any document signed or issued by or on behalf of the company for a particular transaction
The ACN is permanent — it does not change for the entire life of the company, regardless of changes to directors, shareholders, name, or address. It is the company’s unique legal fingerprint.
How a Company’s ABN Relates to Its ACN
When a company applies for an ABN after receiving its ACN from ASIC, the ATO typically creates the ABN by adding a two-digit prefix to the 9-digit ACN. This means a company’s ABN incorporates its ACN.
For example, if a company’s ACN is 123 456 789, its ABN would typically be 36 123 456 789 — the same nine digits with ’36’ added at the front. This is not always the case (the prefix can vary), but it is the most common pattern.
Because the ABN incorporates the ACN in this way, a company can display its ABN on documents where it would otherwise need to show its ACN — provided the ABN follows this format. This saves the company from having to display two separate numbers on every document.
Who Needs What: A Simple Guide by Structure
- Sole trader: ABN only. Apply through abr.gov.au. Free. No ACN.
- Partnership: ABN only (for the partnership entity). Apply through abr.gov.au. Free. No ACN.
- Trust: ABN only (in the name of the trust or trustee). Apply through abr.gov.au. Free. No ACN.
- Company (Pty Ltd, Ltd, etc.): ACN (automatically issued by ASIC on registration) + ABN (applied for separately through ABR or simultaneously via the Business Registration Service). Both are required.
How to Apply: ABN and ACN
Applying for an ABN: Visit abr.gov.au or use the Business Registration Service at business.gov.au. You will need your personal details (TFN, address), details of your business activity, and information about your business structure. The application is free and most ABNs are issued immediately online.
Getting an ACN: You don’t apply for an ACN separately — it is automatically issued by ASIC when you register a company. The ACN appears on your Certificate of Registration. After receiving your ACN, you then apply for your company’s ABN through the ABR or Business Registration Service.
For a step-by-step guide to the full company registration process, including ASIC fees and Director ID requirements, see our guide on how to register a company in Australia.
Common Mistakes With ABN and ACN
- Putting an ACN on a sole trader invoice — sole traders don’t have an ACN; use your ABN only
- Forgetting to display your ABN on invoices — this triggers mandatory 47% withholding by the payer
- Using your old sole trader ABN after incorporating a company — the company needs its own ABN; the individual’s sole trader ABN should be cancelled if the business has fully transitioned
- Treating the ACN and ABN as interchangeable on all documents — while a company’s ABN can substitute for its ACN on many documents, they are issued by different bodies for different purposes and are not universally interchangeable
- Not updating ABN details after a change — you must update your ABN registration within 28 days of any change to your business details; failure to do so can trigger compliance issues
Frequently Asked Questions
Does every business in Australia need an ABN?
Not every business is legally required to have an ABN, but most need one to operate practically. You must have an ABN to register for GST, issue tax invoices, register a business name, and engage with the ATO. Without an ABN, businesses paying you are required to withhold 47% of your invoice amount. The vast majority of businesses — sole traders, partnerships, companies, and trusts — should register for an ABN as a first step.
Can a sole trader have an ACN?
No. ACNs are issued exclusively to registered companies under the Corporations Act 2001. A sole trader operates as an individual, not as a separate legal entity, so no ACN applies. Sole traders use only their ABN for tax invoices, GST registration, and business dealings. If a sole trader decides to incorporate their business as a company, the company receives its own ACN and ABN — separate from the individual’s sole trader ABN.
What happens if I don’t include my ABN on an invoice?
If you fail to quote your ABN on an invoice, the business paying you is legally required under Australian tax law to withhold 47% of the payment and remit it to the ATO. You can recover this withheld amount by lodging your tax return, but it significantly disrupts your cash flow in the meantime. Always include your ABN on every tax invoice.
How do I find a business’s ABN or ACN?
Both are publicly searchable. You can search any ABN using the ABN Lookup tool at abr.gov.au — this shows the business name, ABN status, GST registration, and entity type. You can search any company’s ACN using ASIC’s company search tool at asic.gov.au, which shows the company’s registration details, directors, and current status. Both tools are free and publicly accessible.
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