How to check an ABN (Australian Business Number)

The official, free place to check an ABN is ABN Lookup (abr.business.gov.au), run by the Australian Business Register. No login is needed. This page explains what to look at, and gives you a quick format checker that catches typos before you search.

Step 1: check the number is even possible

An ABN is 11 digits, and the first two are check digits, so most typos produce an impossible number. Paste one here (spaces are fine):

This only checks the format, using the ABR's published method. A number can pass and still not belong to anyone, or be cancelled. Step 2 is what counts.

Step 2: look it up on ABN Lookup

1. Go to abr.business.gov.au.
2. Type the ABN (or a business name) in the search box and search.
3. Open the result and check these fields:
   • ABN status: “Active from …” is what you want. “Cancelled from …” means the ABN is no longer in use.
   • Entity name and type: does the legal name match the person or company you're dealing with? A sole trader shows the person's name; the trading name may differ.
   • Goods & Services Tax (GST): “Registered from …” or “Not currently registered for GST”. This tells you whether GST should appear on their invoices.
   • Business name(s): registered trading names linked to the ABN.
   • Main business location: state and postcode only.
4. Keep a screenshot or note of the date you checked, especially for new suppliers.

Why it matters for a sole trader

• GST credits: if a supplier charges you GST but ABN Lookup says they're not registered for GST, query the invoice before you claim a GST credit for it.
• No ABN, no payment in full: if a supplier doesn't quote an ABN and the payment is over $75 (excluding GST), you generally have to withhold 47% and send it to the ATO, unless an exception applies (for example a signed “Statement by a supplier” for a private hobby).
• Your own details: look yourself up. Your ABN details must be updated within 28 days if they change, and customers will see what's there.
• Your invoices: a tax invoice must show your ABN. Put it on every invoice.

The format check, explained

The ABR's method: subtract 1 from the first digit, multiply each of the 11 digits by the weights 10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, add the results and divide by 89. If there's no remainder, the format is valid. The ABR's example, 51 824 753 556, gives 534, which is 89 × 6.

Sources (checked 17 Oct 2026): ABN Lookup (what it shows; no login; 28-day update rule); ABR Format of the ABN (the checksum method and example); ATO Withholding if ABN is not provided; ATO Tax invoices.

General information, not tax advice. We're not affiliated with the ABR or the ATO; this page just points you to their free tool.

Related

• GST calculator · Invoice number generator · Invoice templates by trade
• Article: Tax invoice vs invoice in Australia: what must be on it