ABN Checker (Australia)
Check that a ABN is correctly formed and that its check digit computes, before you put it on an invoice. Nothing is sent anywhere.
- Free
- No sign-up
- Nothing uploaded
- Updated for 2026
- Last reviewed October 2026
- Reviewed by the Owoode team
- A$ AUD
- GST 10%
- ABN
- A4
- English
Enter a number above.
Example: 51 824 753 556
How the number is built and checked
An Australian Business Number (ABN) has 11 digits: a 9-digit identifier preceded by two check digits. The official check uses modulus 89: subtract 1 from the first (leftmost) digit, multiply each digit by its weighting factor (weights run from 10 to 19), add the products and divide by 89. If the remainder is zero, the number is valid in structure. The Australian Business Register example 51 824 753 556 passes this test.
Passing the arithmetic only shows the number could exist. ABN Lookup (abr.business.gov.au), the free official service, shows whether the ABN is active or cancelled, the business type, GST status, the public details held on the Australian Business Register and historical trading names. It can be searched by ABN, ACN or business name, and no login is needed.
What this does and does not tell you
This page checks arithmetic, not registration. Every ABN carries a check digit calculated from the digits before it, which is what catches a typo. Confirming that a business is genuinely registered means asking Australian Taxation Office (ATO), because only they hold the register.