ABN checker
Check whether an Australian Business Number is correctly written before it goes into your books. This runs the ATO's check-digit test, which catches most typos and misread digits on supplier invoices.
What this check tells you, and what it doesn't
| Question | This check | ABN Lookup |
|---|---|---|
| Is the number correctly written? | Yes | Yes |
| Is the ABN registered and active? | No | Yes |
| Does it belong to this business? | No | Yes |
| Is the business registered for GST? | No | Yes |
So use this as the quick first filter: a number that fails is definitely wrong. For anything that matters, such as a new supplier or a large purchase you plan to claim GST on, confirm the details on ABN Lookup, the free search run by the Australian Business Register.
How the check works
Every ABN is 11 digits. The first two are check digits, worked out from the other nine, so a mistake almost anywhere in the number shows up. The ATO publishes the method:
- Subtract 1 from the first digit.
- Multiply each of the 11 digits by its weight: 10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19.
- Add the results together.
- If the total divides evenly by 89, the ABN is correctly written.
The ATO's own worked example is 51 824 753 556. Try changing one digit of it in the box above and the check will fail.
Why it matters at BAS time
A tax invoice from a supplier needs to show their ABN, and you generally need a valid tax invoice to claim the GST credit on the purchase. An ABN that has been mistyped when an invoice is keyed in, or misread from a scan, is easy to miss and annoying to chase months later. Checking it as the invoice comes in is the cheap moment to catch it.
Ledgr Invoice runs this check on every invoice it extracts, alongside GST and totals checks, and flags the ones worth a second look.
Try it on an invoiceGeneral information only, not tax, accounting or financial advice. Passing the check-digit test does not confirm that an ABN is registered or that a business is registered for GST.