What each one actually is
Three different regulators, three different numbers, and the confusion between them is the whole reason this page exists. An ABN, the Australian Business Number, is an 11-digit identifier issued by the Australian Business Register, which the ATO runs. An ACN, the Australian Company Number, is a 9-digit identifier issued by ASIC, the Australian Securities and Investments Commission, and only a registered company can hold one. A TFN, the Tax File Number, comes from the ATO itself and sits underneath everything else: every individual has their own for life, and a company, partnership or trust holds a second, entirely separate TFN of its own on top of that.
Why a company ends up needing all three
This is the case most people get wrong. ASIC issues a company's ACN automatically the moment the company itself is registered, whether or not it has taken a single order yet. What surprises people is the TFN: a company applies for its own tax file number on a different form from the one an individual uses, and that number belongs to the company, not to any director. A director who has held a personal TFN for years still needs a second, separate one for the company itself. Add the ABN, which follows once the company is actually carrying on an enterprise, almost always true for a trading company, and the three sit together for the entire life of the business.
The sole trader question that is not about headcount
A sole trader never gets a second TFN. Their own personal one, the same number they have always had, covers the business too. What is genuinely conditional is the ABN, and the test has nothing to do with how many people work for them. The Australian Business Register's own guidance is direct about it: an employee, including somebody doing work that is called contracting, is not entitled to an ABN for that activity. Somebody truly carrying on their own enterprise passes a different test and is entitled to one. The two situations can look identical from the outside, doing the same job for the same client, and still land on opposite sides of the same rule.
Needing an ABN is also a separate question from the GST turnover threshold. The ABR states plainly that a person may still need an ABN even while earning below the $75,000 GST registration threshold.
The fourth thing people conflate: a registered business name
A registered business name gets talked about in the same breath as the other three, and it is not the same kind of thing at all. ASIC's own description is simply the name a business operates under: not a separate legal entity, no tax standing, and no protection against somebody using a similar name, only an identical or near-identical one. ASIC's exemption already covers trading under your own name exactly as it stands: a sole trader's first and last name, a partnership trading under all the partners' own names together, or a company trading under its own registered company name. Add anything to that and a registration is generally required, and ASIC normally wants an ABN already in place before it will grant one. An older trap sits behind this one too: an unregistered "trading name" from before the business names register started on 28 May 2012 does not stand in for a registration now.
What it costs, and who to watch out for
An ABN and a TFN are both free to apply for directly, and the ATO says so plainly on its own site. Registering a company, and registering a business name, are different: ASIC charges its own statutory fee for each, re-indexed most years, so no figure is stated here rather than risk printing a stale one. What matters more is the ATO's own warning: fake websites have offered to obtain a TFN or an ABN for a fee while failing to deliver anything, often advertised on social media. Apply directly, or through a registered tax agent, and never through a site that charges for something the government hands over free.
Which of them applies, and where each one is free
This is a reference tool, not a filing service. It tells you which of the four things apply to your structure and why, and points at the free, official process for each, but it does not submit anything on your behalf, and nothing you type here leaves your browser. Where a trust, a dormant company or an unusual structure genuinely sits in a grey area, that is worth a few minutes with an accountant rather than a guess, because the entitlement tests behind an ABN and an ACN are the regulator's own to apply, not this page's.
Common questions
Is it actually free to get an ABN, an ACN or a TFN?
An ABN and a TFN are both free to apply for directly, and the ATO says so in its own words: it is free, quick and easy to apply through the ABR or the ATO. Registering a company is different: ASIC charges its own statutory fee for that, and the ACN comes as part of it rather than as a separate charge. A registered business name carries its own separate ASIC fee too. None of the three genuine identifiers costs anything on its own to apply for.
Does every company really need all three?
Once it is trading, yes, and the part most people miss is the TFN. ASIC issues the ACN automatically the moment the company is registered, whether or not it has started trading. The company then needs its own TFN, applied for separately from any director's personal one, to lodge its own tax return. The ABN follows once the company is actually carrying on an enterprise, which almost every trading company is.
I am a sole trader with no staff. Do I definitely need an ABN?
It turns on what you are doing, not on your headcount. The ABR is direct that an employee is not entitled to an ABN for that work, whatever the arrangement is called, and a genuine hobby with no real commercial activity behind it fails the same test. Somebody carrying on their own enterprise passes it and is entitled to one. Headcount does not come into it either way.
What is the actual difference between an ABN and a TFN?
A TFN is the tax and superannuation system's own reference number, and every individual carries one for life. An ABN identifies a business or enterprise to the wider community, mainly so other businesses can pay it without withholding tax and so it can register for GST. A sole trader has only ever had the one TFN, their own personal one, sitting underneath their ABN. A company, partnership or trust holds a second, separate TFN of its own, on top of anyone's personal one.
Is a registered business name the same thing as an ABN or an ACN?
No, and this is the trap most people fall into. A business name is only a trading name: ASIC's own description is that it is "the name your business operates under." It is not a separate legal entity, it carries no tax standing of its own, and it does not stop somebody using a similar name, only an identical or near-identical one. ASIC generally wants an ABN in place before it will register one.
What actually happens if I do not have an ABN and send an invoice?
Whoever is paying you is generally required to withhold tax at the top rate, 47% since 1 July 2017, from anything over $75 excluding GST, and send that amount to the ATO instead of paying it to you in full. It is not a fine on you directly, but it is a real and immediate cost of leaving an ABN unsorted once you are genuinely trading.
Does a trust need an ACN?
Only indirectly. A trust itself can never hold an ACN, because only a company can. Where the trustee is a company rather than an individual, that trustee company has its own ACN, the same as any other company, but it belongs to the trustee, not to the trust. The trust still needs its own ABN and its own TFN regardless of who the trustee is.
Can I trade under my own name without registering anything extra?
Yes. ASIC's own exemption covers a sole trader using exactly their first and last name, a partnership trading under all the partners' own names together, and a company trading under its own registered company name. Add anything else to that, a slogan, a shortened version, a made-up name, and a business name registration is generally required.