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Invoice ABN Validator
Check Australian ABNs and ACNs on invoices — the real checksum, in bulk.
Quick Tool Overview
The Invoice ABN Validator checks Australian ABNs with the official weighted checksum and ACNs with theirs, in bulk, and explains the 47% withholding that applies when a supplier quotes no ABN at all.
- What it does
- Validates ABNs and ACNs
- You give it
- Numbers, one per line
- You get back
- Checksum verdicts and formatting
- Best for
- Paying Australian suppliers
About the Invoice ABN Validator
An ABN on an invoice is not a formality. If a supplier does not quote one, the payer is required to withhold 47% of the payment and send it to the ATO — so a missing or mistyped ABN is a problem for the person paying, not just the person invoicing.
An ABN carries a real checksum: subtract one from the first digit, weight the eleven digits by a fixed series, and the total must divide by 89. An ACN uses a different weighted rule over nine digits. Both are implemented here, so a transposed pair is caught immediately, one number or a whole column at a time.
What the checksum cannot tell you is whether the ABN is active, who holds it, or whether they are registered for GST — which decides whether their invoice may charge it. ABN Lookup answers all three, free, and every result here says so. Nothing is uploaded.
Key features of the Invoice ABN Validator
Official checksum
The modulus 89 weighted rule for ABNs.
ACNs too
Nine digits with their own check digit.
Formatted output
Grouped the way the ATO writes them.
Withholding explained
Why a missing ABN costs 47%.
Offline
ABN Lookup confirms who holds it; this catches typos.
How to use the Invoice ABN Validator
-
1
Paste the ABNs
Eleven digits each, spaces and all. ACNs are recognised too.
-
2
Read the checksum result
A failure is a typo, every time.
-
3
Check GST registration
On ABN Lookup, before accepting an invoice that charges GST.
-
4
Withhold if there is none
No ABN on a business invoice means 47% withholding.
Frequently asked questions
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 them up, and the total must be divisible by 89.
An ACN is a nine-digit company number from ASIC. An ABN is an eleven-digit business number from the ATO, and for a company it is usually two digits plus its ACN.
No. GST registration is separate, and ABN Lookup shows it. A supplier not registered for GST must not charge it.
No. The checksum runs in your browser.
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