Validate an ABN offline with the ATO’s own checksum, and check your invoice carries what it needs to.
Paste an 11-digit ABN. This checks the format using the ATO’s published checksum — it confirms the number is internally valid, which is a different thing from confirming who it belongs to.
The ATO publishes the algorithm, so anyone can verify a number offline:
10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19.That is the whole test. It catches typos and invented numbers. It cannot tell you whether the business is registered for GST, still trading, or the one you think it is — only the ABN Lookup register can do that, and you should check there before paying a new supplier.
For a customer to claim a GST credit, your invoice has to carry specific things. Work down the list against the invoice in front of you.
Checked against published ATO guidance on 16 September 2026 from secondary sources. Requirements change — confirm the current list on ato.gov.au before relying on it. If a supplier will not give you a valid tax invoice, you generally cannot claim the GST credit.
Two separate questions. The checksum on this page tells you the number is internally valid — it catches typos and made-up numbers, offline and instantly. Whether it belongs to the business you are dealing with, and whether they are registered for GST, is a lookup question: check the free ABN Lookup register at abr.business.gov.au.
Subtract 1 from the first digit, multiply the eleven digits by the weights 10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, add the results, and test whether the total divides evenly by 89. The ATO publishes it, which is why a page like this can check a number without contacting anything.
No. They are separate registrations. A business can hold an ABN and not be registered for GST, in which case it must not charge GST on its invoices. ABN Lookup shows GST registration status and the date it took effect.
Where a supplier does not quote an ABN on an invoice for a taxable supply, the payer may be required to withhold at the top rate and pay it to the ATO. There are exceptions, including for small amounts and for suppliers who are individuals not carrying on an enterprise. Check the current rules on ato.gov.au.
The words "tax invoice", your identity and ABN, the date of issue, a description of what was sold with quantity and price, the GST amount or a statement that the total includes GST, and the extent to which each sale is taxable. Invoices of $1,000 or more also need the buyer’s identity or ABN.
No. The checksum is arithmetic and runs entirely in your browser. There is no lookup call, no server and nothing stored.