What Is an ABN? And Do You Need One as a Sole Trader?

Short answer: An ABN, or Australian Business Number, is a unique 11-digit number that identifies your business to government and the community. The Australian Business Register (ABR) issues it free to anyone carrying on or starting an enterprise in Australia. It doesn’t replace your tax file number: a sole trader keeps their personal TFN and adds an ABN. No law makes a sole trader hold one, but without it, business clients generally have to withhold 47% from payments over $75 (excluding GST), and you can’t register for GST.

The ABN system is run by the Australian Business Register, and this guide reflects the rules for the 2026–27 income year. It explains what the number is and whether you need one. To get one, follow how to apply for an ABN. If you’ve had one for years and can’t remember it, see how to find your ABN.

What does an ABN actually do?

An ABN is a single number you use to deal with government departments and agencies, and that other businesses use to identify you. The ABR’s ABN basics describe it as identifying your business or organisation to the government and community, and note that it doesn’t replace your TFN.

business.gov.au lists what an ABN lets you do. With an ABN you can:

• confirm your business identity to others when ordering and invoicing
• avoid having PAYG tax withheld from payments you receive
• register for GST and claim GST credits
• get an Australian (.au) domain name

The number itself is 11 digits: a 9-digit identifier with two check digits in front, usually written as 12 345 678 901. Those check digits let software spot a mistyped ABN.

Your ABN is also public. ABN Lookup shows your ABN and whether it’s active, your entity name, any business names, the state and postcode of your main business location, and whether you’re registered for GST. It doesn’t show your street address, email or phone number. For a sole trader, the entity name is your own legal name.

What is the difference between an ABN, a TFN and an ACN?

An ABN identifies your business, a TFN is your tax file number with the ATO, and an ACN is the number ASIC gives a company. A sole trader has an ABN and a personal TFN, and no ACN.

Number	Issued by	Who has one	Public?	On your invoices?
ABN (Australian Business Number)	Australian Business Register	Anyone carrying on or starting an enterprise who applies	Yes, on ABN Lookup	Yes
TFN (tax file number)	ATO	Individuals, and separately each company, partnership and trust	No, keep it private	Never
ACN (Australian Company Number)	ASIC	Companies only	Yes	Only if you trade as a company

The ATO’s tax file number guidance is clear on the sole trader point: if you run your business as a sole trader, you use your individual TFN for both business and personal tax. Partnerships, companies and trusts need a TFN of their own. A company gets its ACN from ASIC when it’s registered, and it needs that ACN before it can get an ABN.

A business name is a fourth, separate thing. “Northside Tiling” is a name registered with ASIC, not a number, and it doesn’t replace your ABN. You can link several business names to one ABN.

Does a sole trader need an ABN?

In practice, yes, if you’re running a genuine business. No law forces you to have one, but trading without one costs you money and closes off GST registration.

The cost comes from the withholding rule. If you don’t quote an ABN and a payment for goods or services is more than $75 excluding GST, the payer generally has to withhold at the top rate of tax and send it to the ATO. That’s 47%: the 45% top marginal rate plus the 2% Medicare levy.

Say a freelance photographer invoices a business $2,000 for a shoot and leaves the ABN off:

	With an ABN	Without an ABN
Invoice	$2,000	$2,000
Withheld by the client and sent to the ATO	$0	$940
Paid to the photographer now	$2,000	$1,060

The photographer gets the $940 back only as a credit when they lodge their tax return, which may be many months later. Most business clients will simply ask for an ABN before they pay.

The rule is aimed at payments made by businesses, and it has exceptions, such as a supply that is private or domestic in nature or part of a hobby rather than a business. But GST registration needs an ABN whoever your clients are, so once your turnover heads towards $75,000 you’ll need one anyway. How to become a sole trader covers the other registrations.

Who can get an ABN, and who can’t?

You can get an ABN if you’re carrying on or starting an enterprise in Australia. You can’t get one for work you do as an employee.

The ABR’s entitlement rules look for activity that is commercial, done with the aim of making a profit, repeated and systematic, and carried on like other businesses in the same industry. An individual who meets that test is entitled to an ABN as a sole trader. A one-off sale or a hobby doesn’t qualify.

Employees aren’t entitled, even when the arrangement is called contracting. The ABR gives apprentices, trade assistants and labourers as examples, and says an employer shouldn’t make getting an ABN a condition of a job. If you’re not sure which you are, read contractor vs employee in Australia before you apply.

Does it cost anything to get an ABN?

No. The ABR charges no fee to apply for an ABN, online or on paper.

You apply through the government’s Business Registration Service or the ABR. If your details can be verified, the ABN usually appears when you finish the form; otherwise it can take up to 28 days. Websites that charge a fee to “register your ABN” aren’t the government, so check that the address ends in .gov.au before you enter your TFN. How to apply for an ABN walks through the form step by step.

Can you have more than one ABN?

Not as a sole trader. You can run any number of businesses under one ABN as long as they share the same business structure.

So a sole trader who does carpentry during the week and sells furniture at weekend markets uses the same ABN for both, and can link a separate business name to each. You need a second ABN only when a business runs under a different structure. If you set up a company or a partnership, that entity gets its own ABN, and you keep your sole trader ABN for anything you still do in your own name.

Does having an ABN mean you’re registered for GST?

No. An ABN and GST registration are separate. Most sole traders hold an ABN for years before they register for GST, and many never do.

You must register for GST within 21 days once your GST turnover reaches $75,000, or before your first trip if you drive a taxi or ride-sourcing vehicle. Until then, your invoices show your ABN but no GST, and they mustn’t be called tax invoices. ABN Lookup shows anyone whether a business is registered for GST, which is worth checking before you pay a supplier’s GST. How to register for GST covers the threshold and the steps.

Once you have an ABN, you must keep your details up to date within 28 days of a change, and cancel it when the business stops.

Where does your ABN go, and where does Keel fit?

Your ABN belongs on every quote, invoice and receipt you issue, and the paperwork behind those documents is what you’ll need at tax time.

Keel: Invoice Maker & Receipts, by Ilura Technology OÜ, is an iPhone app for keeping that paperwork. You write estimates, and an accepted estimate becomes the invoice in one tap. Invoices are PDFs, and every quote, receipt, expense and invoice is kept under its job, alongside your customers and business mileage. A “who owes you” list drafts reminders that you review and send yourself; nothing is sent automatically. Records stay on your iPhone: no account, no bank connection, no cloud sync, and the App Store privacy label reads “Data Not Collected”.

Keel doesn’t apply for an ABN, register you for GST, lodge anything or connect to the ATO or the ABR. It’s a record keeper. It’s free with no invoice limit, and free invoices carry a small “Made with Keel” footer. Keel Lifetime is a one-time purchase ($249.99 USD; the App Store shows your local price) that adds custom branding, a signature, premium templates and accountant-ready exports. Keel on the App Store. The Australia guides cover GST, BAS and tax next.

Frequently asked questions

Is an ABN the same as a TFN? No. An ABN identifies your business and is public on ABN Lookup. A TFN is your private tax file number with the ATO and should never appear on an invoice. As a sole trader you use your personal TFN for your business and personal tax, and the ABN sits alongside it. Companies, partnerships and trusts each have their own TFN as well as an ABN.

Is an ABN free? Yes. The Australian Business Register charges nothing to apply for an ABN, online or on paper. Apply yourself through the Business Registration Service at register.business.gov.au or through abr.gov.au. Sites that charge for an ABN are private services, not the government, and you don’t need them.

Do I need an ABN as a sole trader? If you run a genuine business, you’ll almost certainly want one. Without an ABN, a business client generally has to withhold 47% from any payment over $75 excluding GST, and you can’t register for GST. Employees aren’t entitled to an ABN for their employment, and a hobby isn’t a business, so neither needs one.

How many digits is an ABN? An ABN has 11 digits: a 9-digit identifier with two check digits in front. It’s usually written in groups, such as 12 345 678 901. If a number someone gives you doesn’t have 11 digits, or doesn’t come up on ABN Lookup, it isn’t a valid ABN.

Can I use one ABN for more than one business? Yes, as a sole trader. You can run any number of businesses or activities under the same ABN as long as they all use the same structure, and you can link several business names to it. A company, partnership or trust is a different structure and needs its own ABN.

How do I check if an ABN is real? Search the number on ABN Lookup at abr.business.gov.au. It’s free and needs no login. It shows whether the ABN is active or cancelled, the entity’s name, any business names and whether the business is registered for GST. Check before you pay a new supplier, particularly one charging GST.

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This article is general information, not tax advice. Consult a qualified Australian tax professional.