ABN validator: is this number even possible?
Type an ABN into our free ABN validator and it checks the eleven digits against the ATO check digit method as you go, so you know straight away whether the number could be real.
Nine digits? You may be holding an ACN.
An ABN and an ACN look alike on an invoice, but they're different lengths and do different jobs.
An ABN has eleven digits. An ACN has nine digits and belongs to a company registered with ASIC.
A company's ABN usually contains its ACN as its last nine digits. So if you've typed nine digits from a company invoice, the ABN is likely printed nearby with two more digits in front.
These rules come from the ATO and the Australian Business Register. Confirm the details on their websites before you rely on them.
Why a real ABN fails: five common slips
Most numbers that fail aren't made up. They were typed or copied with one small slip. Here's what to look for before you ask the business again.
One digit missing
Ten digits can never be an ABN. Count again from the invoice, because a dropped digit often hides where a number wraps onto a second line.
One digit too many
Twelve digits usually means a key was pressed twice. Retype the number slowly, reading it in small groups.
Two digits swapped
A swap moves each digit onto a different weighting, so the total shifts and the test usually fails. Check pairs that sit side by side.
Letters or stray characters pasted in
Copying from an email or PDF can bring in a dash, a full stop or a letter O where a zero belongs. Clear the box and type the eleven digits only.
An ACN in the ABN box
Nine digits is the length of an ACN, the company number, not an ABN. Look on the invoice for a separate eleven-digit ABN.
01 · 01
Start with eleven digits
An ABN always has eleven digits. Count them before anything else. Ten or twelve means a digit was missed or doubled, and the number cannot be an ABN.
02 · 02
Take one from the first digit
Subtract one from the first digit only. The other ten digits stay exactly as they are. It's a small step, but skip it and the whole result comes out wrong.
03 · 03
Multiply each digit by its weighting
Each of the eleven positions has its own weighting, set by the ATO. Multiply every digit by the weighting for its position. We don't reprint the weightings here, because the ATO website is the place to read them.
04 · 04
Add the eleven results together
Add all eleven answers to get one total. That single number is what decides whether the ABN format holds up.
05 · 05
The total must divide evenly by eighty-nine
If the total divides by eighty-nine with nothing left over, the number passes. Anything left over means the number cannot be an ABN, however neat it looks on paper.
06 · 06
Confirm the method with the ATO
This method comes from the ATO, and our box runs it for you as you type. If you're building your own check, read the method on the ATO website. This is general information only, so confirm with the ATO or your accountant before relying on it.
Questions about ABN check digits
Frequently Asked Questions
- Can a valid number still be unregistered?
- Yes. The check digit test only shows that the digits fit the ATO pattern. Plenty of digit strings pass without any business holding them, and an ABN that was issued can later be cancelled. Search the number to see whether it's on the register, its status and the date that status took effect.
- Why did my copied number fail?
- Copying often brings something extra along. Look for a dash, a full stop, a letter O in place of a zero, or a lower-case L in place of a one. A digit can also drop off where the number wrapped onto a new line. Clear the box and type the eleven digits by hand.
- Do spaces matter?
- ABNs are often printed in small groups so they're easier to read. The spaces are not part of the number, and the check digit test only uses the eleven digits. If a spaced number fails, retype it as eleven digits with nothing else in the box.
- Does the box check ACNs too?
- Yes. The same search box takes an ABN, an ACN or a business name. As you type a number, it checks the digits and tells you when the number cannot be a real ABN or ACN.
- Is this the ATO's own tool?
- No. ABN Checker is an independent website and is not part of or endorsed by the ATO or the Australian Business Register. The check digit method comes from the ATO, so confirm it on the ATO website if you need to rely on it.
Got a number? Find out if it could be real.
Type it into the box and the check digit test runs as you go. If it passes, search it to see status and GST.
Free, no account. The box checks the digits as you type.