When do you need to register for an ABN in Australia?

You need an Australian Business Number (ABN) when you are carrying on an enterprise. This includes operating a business as a sole trader, running a side hustle with regular clients, operating a company or trust, or providing goods and services for payment on a regular and repeated basis. A one-off sale (like selling personal items) does not require an ABN.

If you provide services without an ABN, the payer is required by law to withhold 47% of the payment and remit it to the ATO. This is the no-ABN withholding rule and can significantly affect your cash flow. Providing your ABN to clients prevents this from happening.

Registering for an ABN is free through the Australian Business Register (ABR). You apply with your tax file number. Once you have an ABN, you can also register for GST if your turnover is expected to reach $75,000 or more in 12 months (or $150,000 for non-profit organisations). Having an ABN does not automatically register you for GST; you must register separately. ABN registration also enables you to register a business name and enter certain government contracts.