ABN check
Is that ABN actually valid?
Every ABN carries its own check digits. Paste one in and the arithmetic is verified on your device — useful before you put a number on an invoice, or pay one.
Checks the mathematics of the number only. It confirms the digits are self-consistent — it does not tell you who the number belongs to or whether the business is registered for GST. For that, use the government register at abr.business.gov.au.
What the number tells you
Valid is not the same as real
A number that passes is internally consistent — the digits agree with their own checksum. That catches typos, transposed digits and invented numbers, which is most of what goes wrong.
It does not prove the ABN is active, belongs to the business quoting it, or is registered for GST. Only the government register can tell you that, and it is free: abr.business.gov.au.
Why it matters on an invoice
If a supplier invoices a business without a valid ABN, the payer may be required to withhold tax from the payment. Checking the number before you pay, or before you send, avoids a problem later.
ABN and ACN
| Attribute | ACN | ABN |
|---|---|---|
| Digits | 9 | 11 |
| Issued by | ASIC | ATO / ABR |
| Applies to | Companies | Any business entity |
A company's ABN is usually its ACN with two extra digits in front. The box above picks the right algorithm from the length.
Related
- Putting the number on a document: tax invoice maker.
- Why a missing ABN costs you money: invoice mistakes.
- Work out the GST on the amount you are invoicing.
ABN questions
How do I check if an ABN is valid?
An ABN carries its own check digits. Paste the 11 digits above and the arithmetic is verified instantly on your device. A number that fails has been mistyped or invented.
Does this tell me who owns the ABN?
No. This checks the mathematics only. To see the business name, status and GST registration, use the government's own register at abr.business.gov.au — that is the authoritative source and it is free.
How does the ABN check digit work?
Subtract 1 from the first digit, multiply each of the 11 digits by a fixed weighting, add the results, and a valid ABN divides exactly by 89. It is published by the ATO, which is why this can run without any lookup.
What is the difference between an ABN and an ACN?
An ACN is a 9-digit company number issued by ASIC when a company is registered. An ABN is an 11-digit business number used for tax. A company's ABN is usually its ACN with two digits in front. Paste either above — the length tells us which to check.
Is my ABN sent anywhere?
No. The check is arithmetic performed in your browser. Nothing is transmitted, logged or stored.