What is the relationship between an ACN/ARBN and an ABN?

When you register for an Australian business number (ABN), we will use your Australian Company Number (ACN) or Australian Registered Body Number (ARBN) to create your ABN. Your ABN is actually two check digits followed by the nine existing digits of your ACN or ARBN.

You can use your ABN in place of your ACN or ARBN provided:

your ABN includes your ACN or ARBN in the last nine digits
you quote your ABN in the same way as you quote your ACN or ARBN. For example, if you use your ACN and your legal name on your letterhead, you can use your ABN in place of your ACN.