ABN (Australian Business Number)
The 11-digit number that identifies your business.
An ABN is a unique 11-digit number that identifies your business to the government, other businesses and the ATO. You put it on invoices, use it to register for GST, and quote it so clients don’t have to withhold tax from your payments. It’s free to apply for and you can be a sole trader with just an ABN.
An ABN identifies your business; a TFN identifies you as a taxpayer. You keep both, and a sole trader lodges business income under their personal TFN using the ABN on invoices. Registering for an ABN doesn’t register you for GST — that’s a separate step you take once your turnover reaches the threshold, or earlier if you choose to.
Worked example
An ABN is formatted as 11 digits, usually written in a 2-3-3-3 pattern like 51 824 753 556 (that one is the ATO’s own). On an invoice it sits near your business name, and once you’re registered for GST the same invoice becomes a tax invoice showing the GST separately.
Common mistake
Leaving your ABN off an invoice. Without it a business client generally has to withhold 47% of the payment and send it to the ATO — you get it back at tax time, but you have waited a year for money that could have been in your account that week.
Grounded in ATO guidance. Figures last checked . General information, not tax advice.
Related terms
Sole trader
The simplest business structure — you and the business are one.
TFN (Tax File Number)
Your personal reference number in the tax system.
GST (Goods and Services Tax)
Australia’s flat 10% tax on most goods and services.
Cost of goods sold (COGS)
What the things you actually sold cost you to make or buy.
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Questions about this term
ABN (Australian Business Number): common questions
- What happens if I leave my ABN off an invoice?
- A business client generally has to withhold 47% of the payment and send it to the ATO. You get it back at tax time, but you have waited a year for money that could have been in your account that week. Quoting the ABN on every invoice is what stops the withholding.
- Does getting an ABN register me for GST?
- No — they are separate steps. An ABN identifies your business; GST registration is something you do once your turnover reaches the threshold, or earlier if you choose. Once you are registered, the same invoice that carries your ABN becomes a tax invoice showing the GST separately.
- Does an ABN cost anything to get?
- No — it is free to apply for, and you can be a sole trader with just an ABN. It is an 11-digit number, usually written in a 2-3-3-3 pattern, that goes on your invoices, is used to register for GST, and is quoted so clients don’t have to withhold tax from your payments.
- Do I still need a TFN if I have an ABN?
- Yes — you keep both. The ABN identifies your business; the TFN identifies you as a taxpayer. A sole trader lodges business income under their personal TFN, using the ABN on invoices. The TFN stays private; the ABN is the number meant to be seen.
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