An Australian Business Number (ABN) is an 11-digit identifier issued by the Australian Business Register (ABR). You need one if you're carrying on a business in Australia — whether as a sole trader, partnership, company, or trust.
Applying is free and takes about 10 minutes at abr.gov.au. You'll need your Tax File Number (TFN), identity documents, and details about your business activities. Most sole traders and companies receive their ABN immediately; trusts and partnerships may take up to 28 days.
Having an ABN allows you to: issue tax invoices, claim GST credits (if GST-registered), avoid having clients withhold 47% from payments to you (the no-ABN withholding rule), register a business name, and open a business bank account.
After registration, consider whether you also need to: register for GST (mandatory if turnover exceeds $75,000), register a business name with ASIC (your ABN alone doesn't give you a trading name), and register for PAYG withholding if you plan to hire employees. Your ABN must appear on all invoices and business documents.