A TFN (Tax File Number) identifies you personally as a taxpayer; an ABN (Australian Business Number) identifies your business. You get a TFN once, generally as a teenager or when you start your first job, and keep it for life. You get an ABN separately, only once you're actually carrying on an enterprise, a sole trader business, a side hustle, contracting or ride-share work. Most working Australians who run any kind of business end up holding both, for different jobs.
What each number is actually for
Your TFN is your personal reference number with the ATO. It's attached to you as an individual, follows you for life regardless of what jobs or businesses you go through, and is used for lodging tax returns, having tax withheld correctly from wages, reporting bank interest, and dealing with Centrelink and super funds. Without one, an employer must withhold tax from your pay at the top marginal rate. There's no ABN equivalent to this; it's purely a "who are you as a taxpayer" number.
Your ABN is your business's identifier. It's the number you put on invoices, use to register for GST, and quote to other businesses so they don't have to withhold from what they pay you. It doesn't replace your TFN, a sole trader has one TFN (themselves) and one ABN (their business), and both numbers show up in different places on the same tax return.
Side by side
| TFN | ABN | |
|---|---|---|
| Stands for | Tax File Number | Australian Business Number |
| Digits | 9 | 11 |
| Issued by | Australian Taxation Office | Australian Business Register (ATO) |
| Who has one | Every individual taxpayer, plus companies, trusts and partnerships | Anyone carrying on an enterprise: sole traders, partnerships, trusts, companies |
| What it's for | Lodging tax returns, correct PAYG withholding on wages, bank interest, Centrelink, super | Invoicing, avoiding no-ABN withholding, GST registration, dealing with other businesses |
| When you get one | Generally as a teenager, or before your first job | Only once you start an enterprise. Not automatic, and not everyone needs one |
| Cost | Free from the ATO | Free from the ABR ($99 agent-lodged with review) |
Do sole traders get a separate business TFN?
No. This is the mix-up that catches people out. A company, trust or partnership gets its own TFN, separate from the TFNs of the people who run it. A sole trader doesn't. If you're operating as a sole trader, your business income and expenses are reported on your own individual tax return, under your own personal TFN. The ABN sits alongside it to identify the business side of what you do, but it isn't a second tax identity. One person, one TFN, however many ABNs or business names they operate under.
When you actually need which one
You need a TFN almost immediately once you're earning any income, a casual job, a first payslip, interest on a savings account. Skip it and your employer or bank withholds tax at the top rate until you provide one, which is a rough way to find out you needed it.
You need an ABN only once you cross from "earning wages" into "running a business or enterprise", driving for Uber or DiDi, freelancing, contracting, or selling anything with an expectation of profit. The trigger to actually apply is usually your first invoice to a business: without an ABN quoted on it, the payer is required to withhold 47% of what they owe you and send it to the ATO instead. That's not a technicality. It happens by default, and it's the single biggest reason people apply for an ABN before their business technically "needs" one on paper.
If your turnover is heading past $75,000 (or you're a taxi or rideshare driver, where the rule applies from the first dollar), you'll also need to register for GST, a separate step again, usually bundled with the ABN application.
Getting both sorted
If you're a first-time earner without a TFN yet, that has to come first. It's a free application direct with the ATO and isn't something we lodge on your behalf. Once you have a TFN, applying for an ABN takes about five minutes: the application asks for your TFN to verify your identity against ATO records, which is what lets a clean application clear same-day instead of sitting in manual review. If you're weighing up whether you're a sole trader or should be looking at a company structure instead, the practical differences are covered in our ABN vs ACN guide; if you're just trying to work out whether you need an ABN at all yet, here's what it actually costs and what you get for it.
Common questions
Can I use my TFN instead of an ABN when I invoice someone?
No. A TFN identifies you as an individual taxpayer; it doesn't tell a business you're operating an enterprise. If you invoice a business without quoting an ABN, they're generally required to withhold 47% of the payment and send it to the ATO, quoting your TFN instead doesn't stop that.
Do I need a TFN to apply for an ABN?
Not strictly, but it's the difference between a same-day approval and a manual review that can take weeks. Providing your TFN lets the ABR verify your identity electronically against ATO records; without it, your application is more likely to be flagged for paper-based checks.
Does a sole trader get a separate business TFN?
No. Sole traders use their individual TFN for everything, business included, business income and expenses go on the same personal tax return under the same TFN, alongside an ABN that identifies the business itself. Only companies, partnerships and trusts get their own separate TFN.
I already have a TFN: do I automatically get an ABN too?
No, they're separate registrations for separate purposes. A TFN is issued once you're old enough to need one for tax purposes, generally when you start earning income. An ABN is only issued once you're actually carrying on an enterprise (a side hustle, contracting work, a sole trader business) and you apply for it separately, even though your TFN helps verify who you are.
What happens if I lose or forget my TFN?
It's not reissued to you over the phone for security reasons. You can find it on a past notice of assessment, income statement, or superannuation statement, or log in to myGov (linked to the ATO) to view it. If none of those work, the ATO can verify your identity and help you retrieve it.
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