An Australian Company Number or ACN is the registration number issued to a new company registered in Australia. Only companies are issued with an ACN by the Australian Securities and Investments Commission (ASIC) and they provide a unique identity code for monitoring activities within the structure of the Corporations Law of Australia.
An Australian Business Number or ABN is a unique 11 digit number issued by the Australian Taxation Office (ATO) to all entities that are in business including sole traders, companies, trusts and partnerships. All businesses irrespective of size or turnover must apply to the ATO to obtain an ABN and you must display that ABN on all your invoices.
There is often confusion between the two numbers because the ATO uses the Australian Company Number as the basis for a company's ABN. A company's ABN will always be two digits followed by the 9 digits of their ACN. While every business needs an ABN, not every business entity has to register for GST. If your annual turnover (or projected revenue) will not exceed $75,000 per annum you don’t need to register.
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