Published: November 2025
When starting or operating a business in Australia, you will encounter various registration numbers and identifiers. The three main numbers are ABN (Australian Business Number), ACN (Australian Company Number), and ARBN (Australian Registered Body Number). Understanding which numbers you need, how they differ, and where you must display them is essential for compliance and avoiding penalties.
In Australia, there are over 2.5 million active ABNs registered, representing sole traders, partnerships, companies, and trusts. Companies account for approximately 800,000 of these registrations, each holding both an ACN and ABN. Foreign companies operating in Australia must also register for an ARBN and can then apply for an ABN.
This article explains each registration number in detail, clarifies who needs which numbers, outlines display requirements, and provides practical guidance for Australian business owners.
An ACN is a unique nine-digit number issued by the Australian Securities and Investments Commission (ASIC) when you register a company. Every company incorporated in Australia receives an ACN automatically upon registration. This number permanently identifies your company and remains the same even if you change the company name, restructure, or eventually deregister.
The ACN serves as the primary identifier for all ASIC records, company searches, and official documentation. Unlike ABNs which apply to various business structures, ACNs are exclusive to companies.
Only companies registered with ASIC receive an ACN. This includes proprietary limited companies (Pty Ltd), public companies, and company limited by guarantee structures. Sole traders, partnerships, and trusts do not receive ACNs because they are not incorporated as companies.
When you register a company through ASIC or a registered agent, the ACN is issued automatically as part of the registration process. You cannot choose or customise your ACN.
ASIC regulations require companies to display their ACN on specific documents to ensure transparency in business dealings.
Required display locations:
Not required on:
Real example: A Sydney consulting company must include their ACN on email quotes sent to clients (these are written advertisements making specific offers) and invoices, but not on business cards handed out at networking events.
When displaying your ACN, use the format "ACN XXX XXX XXX" with spaces separating each three-digit group. For example, ACN 123 456 789. Some businesses include the ACN in email signatures, on invoice footers, and company letterheads alongside their business name.
An ABN is an 11-digit unique identifier for businesses operating in Australia, issued by the Australian Business Register (ABR), which is operated by the Australian Taxation Office (ATO). The ABN identifies your business for tax and administrative purposes, making it easier to interact with the ATO, suppliers, and customers.
For companies, the ABN typically incorporates the nine-digit ACN with a two-digit prefix. For example, if your ACN is 123 456 789, your ABN might be 65 123 456 789. The two-digit prefix is algorithmically generated to create a unique 11-digit number.
You should register for an ABN if you are operating an enterprise in Australia, regardless of structure. This includes sole traders, partnerships, companies, and trusts. The key question is whether you are carrying on an enterprise, which generally means any business, trade, or commercial activity.
When you need an ABN:
When you might not need an ABN:
Confirm business identity: Your ABN appears on invoices, quotes, and correspondence, allowing customers and suppliers to verify your business is legitimate through the ABN Lookup tool.
Avoid PAYG withholding: When you provide services to other businesses without quoting an ABN, they must withhold 47% of the payment and remit it to the ATO. Providing your ABN prevents this withholding.
Claim GST credits: Only businesses registered for GST with an ABN can claim input tax credits on business purchases. For businesses purchasing $10,000 in equipment, that is $909 in GST credits you can claim.
Access energy grants: Certain fuel tax credits and energy grants require an active ABN.
Register domain names: The .com.au and .net.au domain name extensions require an Australian ABN.
Required display locations:
Critical compliance point: If you are registered for GST and issue a tax invoice without displaying your ABN, and the total payment exceeds $75, the payer must withhold tax at the top marginal rate. This is a costly mistake that affects cash flow immediately.
A Melbourne graphic designer invoiced a corporate client $5,000 without including their ABN. The client withheld $2,350 (47%) and remitted it to the ATO. The designer eventually recovered the amount through their next tax return, but suffered immediate cash flow impact.
Register online through the ABR website or the Business Registration Service. The application is free for most business structures.
Information you need:
For company directors who are Australian residents: Provide your TFN for identity verification during the application process.
For non-resident directors: Provide certified copies of identity documents including passport and proof of overseas address. This verification process can take several weeks, so start early if time is critical.
Real example: A Brisbane couple registering an ABN for their online retail business needed their individual TFNs, details of the business structure (they chose partnership), estimated annual turnover ($180,000), and industry code (clothing retailing). Their ABN was issued within minutes of online application.
You must cancel your ABN when you close your business permanently, change business structure requiring a new entity, or cease operating the business even temporarily for extended periods.
Structure changes requiring new ABNs:
When you change structures, the new entity requires its own ABN. For example, a sole trader incorporating must register a company (receiving an ACN), then apply for a new ABN in the company's name. The sole trader ABN should then be cancelled.
An ARBN is a unique nine-digit number issued by ASIC to foreign companies and other bodies that register in Australia but are not incorporated as Australian companies. While the ACN identifies Australian companies, the ARBN identifies foreign entities operating in Australia.
Foreign companies must register with ASIC before conducting business in Australia. Upon registration, they receive an ARBN rather than an ACN. This maintains their foreign corporate identity while providing an Australian registration number for compliance purposes.
Foreign companies: Companies incorporated overseas that want to carry on business in Australia must register with ASIC and receive an ARBN. For example, a US corporation opening an Australian branch must register with ASIC for an ARBN.
Other registered bodies: Certain entities that register with ASIC but are not companies, such as some types of incorporated associations or foreign trusts.
Entities with an ARBN can also apply for an ABN to operate in Australia's tax system. The ARBN serves as the ASIC identifier, while the ABN serves as the tax and business identifier. Most foreign companies operating in Australia need both.
Real example: A Singapore technology company establishing an Australian office registers with ASIC for an ARBN. They then use this ARBN to apply for an Australian ABN, allowing them to invoice Australian customers, register for GST, and comply with tax obligations.
Under the Corporations Act, entities must display their ARBN on all public documents and negotiable instruments published and signed in Australia. This includes invoices, contracts, letters, receipts, and other business documents similar to ACN requirements for Australian companies.
The display format is "ARBN XXX XXX XXX" with spaces separating each three-digit group, similar to ACN formatting.
Sarah starts a photography business in Perth. She operates as a sole trader, not a company.
Numbers needed:
Why: Sole traders are not companies, so they do not receive an ACN. Sarah needs an ABN to invoice clients, avoid PAYG withholding on payments, and potentially register for GST if her turnover exceeds $75,000.
Display requirements: Sarah includes her ABN on all invoices, quotes, and business correspondence.
Michael and Lisa register a company called Bright Future Consulting Pty Ltd in Sydney to provide business advisory services.
Numbers needed:
Why: All Australian companies receive an ACN from ASIC. They then apply for an ABN for tax and business purposes.
Display requirements: The company must display both ACN and ABN on invoices, company letterheads, contracts, and other official documents. Most businesses show both numbers together, for example: "Bright Future Consulting Pty Ltd | ACN 123 456 789 | ABN 65 123 456 789"
A New Zealand construction company wins contracts in Brisbane and needs to establish an Australian presence.
Numbers needed:
Why: Foreign companies must register with ASIC before carrying on business in Australia, receiving an ARBN. They then need an ABN for tax compliance and invoicing Australian clients.
Display requirements: Display both ARBN and ABN on all Australian business documents, invoices, and contracts.
James and Rebecca form a partnership to operate a marketing agency.
Numbers needed:
Why: Partnerships are not incorporated companies, so they do not receive an ACN. They need an ABN for the partnership entity.
Important note: Each partner also provides their individual TFN when registering the partnership ABN.
The Smith Family Trust holds property investments and receives rental income.
Numbers needed:
Why: Trusts conducting business or investment activities should obtain an ABN. If the trustee is a company, that company has its own ACN and ABN separate from the trust's ABN.
Display requirements: When the trust issues invoices for rental income or other business activities, display the trust's ABN, not the trustee's ABN.
These are three different numbers for different purposes. Your Tax File Number is personal and identifies you for individual tax purposes. Your ABN identifies your business entity for tax and administrative purposes. Your ACN identifies your company with ASIC if you operate through a company structure.
Never display your TFN publicly on invoices or websites. Only provide TFN to the ATO, your accountant, and in specific circumstances like superannuation reporting.
ABNs are not effective until their registered start date. If you backdate your ABN start date, ensure you do not use it before that date. Applying for an ABN in November with a December start date means you cannot issue ABN invoices until December.
When your business changes address, structure, name, or activities, update your ABN registration within 28 days. Failure to maintain current details can result in ABN cancellation.
A Canberra business moved premises and changed their business name but did not update the ABR. When a major customer checked their ABN details, the information appeared outdated and the customer delayed payment pending verification. Always update the ABR immediately when details change.
Sole traders and partnerships sometimes incorrectly display "ACN" on business documents. Only companies have ACNs. If you operate as a sole trader, display your ABN only.
Missing your ABN or ACN on documents where required can result in penalties and practical problems. ASIC can fine companies up to $1,700 for failing to display their ACN correctly. Missing ABN on invoices results in PAYG withholding on payments.
The ABR provides a free ABN Lookup service where anyone can verify business details. Enter an ABN, business name, or ACN to see the entity name, entity type, ABN status (active or cancelled), GST registration status, and ABN registration date.
Use ABN Lookup to verify customers before extending credit, confirm supplier details before making payments, and check that your own ABN displays correctly.
ASIC provides company search services showing company details including ACN, registration date, current and former names, officeholders (directors and secretaries), and registered office address. Some information is free, while detailed company extracts cost approximately $9 to $39 depending on detail level.
Use ASIC Connect to verify companies before entering major contracts, conduct due diligence on potential business partners, and confirm director details.
What is the difference between an ABN and an ACN?
An ACN is issued by ASIC exclusively to companies and serves as the company identifier for ASIC records and official documents. An ABN is issued by the ABR to any business entity including sole traders, partnerships, companies, and trusts, serving as the business identifier for tax and administrative purposes. Companies have both an ACN and an ABN.
Do I need both an ACN and an ABN for my company?
Yes. When you register a company with ASIC, you automatically receive an ACN. You then apply separately for an ABN through the ABR. Most companies need both numbers to operate legally and comply with tax and corporate regulations.
Can I operate without an ABN?
You can legally operate some businesses without an ABN, particularly if your turnover is below $75,000 and you do not need to register for GST. However, operating without an ABN means businesses paying you must withhold 47% tax from payments, you cannot claim GST credits, and you cannot register a .com.au domain. Most businesses should register for an ABN regardless of turnover.
How long does it take to get an ABN?
For Australian residents with a TFN, ABN registration is instant when applying online. You typically receive your ABN immediately upon submitting the application. For non-residents or applications requiring additional verification, processing can take 2 to 4 weeks. Company ABN applications after ASIC registration are also instant for directors with TFNs.
What happens if I trade using an incorrect or cancelled ABN?
Using a cancelled or incorrect ABN on invoices means businesses paying you must withhold tax, you cannot claim GST credits even if registered for GST, and you may face compliance issues with the ATO. Check your ABN status regularly through ABN Lookup and ensure it remains active.
Can I change my ABN or ACN?
No. ABNs and ACNs are permanent numbers assigned to specific entities. If you change business structure (for example, from sole trader to company), the new entity receives a new ABN and possibly ACN. You cannot transfer your existing ABN to a different entity or request a different number for the same entity.
Do I need an ABN for a side business or hobby?
If your activity is genuinely a business or enterprise (profit-motivated, regular, organised), you should register for an ABN even if it is part-time or secondary income. Hobbies or personal activities not conducted as a business generally do not require an ABN. The ATO provides guidance on distinguishing business from hobby based on factors like profit intention, regularity, and commercial nature.
What is the format for displaying an ABN or ACN on documents?
ABNs display as 11 digits grouped as XX XXX XXX XXX. For example, ABN 53 123 456 789. ACNs display as 9 digits grouped as XXX XXX XXX. For example, ACN 123 456 789. Companies typically display both together: "Company Name Pty Ltd | ACN 123 456 789 | ABN 53 123 456 789"
Can foreign businesses operate in Australia without an ARBN?
Foreign companies carrying on business in Australia must register with ASIC and obtain an ARBN unless they fall under specific exemptions (for example, limited activities through Australian agents). Operating without required ASIC registration can result in significant penalties and limits your ability to enforce contracts in Australian courts.
How do I cancel my ABN when closing my business?
Cancel your ABN online through the ABR website or by contacting the ATO. You need to finalise all tax obligations including final BAS if registered for GST, final income tax return, and cancellation of GST registration before ABN cancellation. Companies must also arrange ASIC deregistration separately, which cancels the ACN.
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