How to check an ABN (a supplier's, before you pay)

By CostCode. Last reviewed 30 Sep 2026 against the official sources below, including the ATO's guidance.

To check an ABN, search it on ABN Lookup, the Australian Business Register's free public search. It shows whether the ABN is active, who it belongs to and whether it's registered for GST. Do it once for every new supplier, before the first payment, and again when an invoice's details change.

Check an ABN's digits

Type or paste the 11 digits from the invoice. This checks the ABR's check-digit calculation, in your browser. Whether the ABN is registered, active and the supplier's is on ABN Lookup.

ABN

Search ABN Lookup

In short

Search the ABN on ABN Lookup, the ABR's free public search: it shows whether the ABN is active, who it belongs to and whether it's registered for GST.(ABR: ABN Lookup)
Check the name on the invoice is on the ABN's record, and that on the invoice date the ABN was active, and registered for GST if the invoice charges GST.(ABR: ABN Lookup)
If a supplier gives you no ABN, the ATO says you generally withhold tax at the top rate from a payment over $75 excluding GST.(ATO: Withholding if ABN is not provided)

Check an ABN on ABN Lookup, step by step

ABN Lookup needs no login and costs nothing. With the supplier's invoice in front of you:(ABR: ABN Lookup)

Open ABN Lookup (abr.business.gov.au) and type the 11 digits from the invoice into the search box. Spaces don't matter.
Open the result. The current details come first; a tab beside them shows the historical details.
Read the ABN status: active, and since when, or cancelled.
Check the name: the entity name, or one of the business names listed, should be the business billing you.
If the invoice charges GST, check the GST line says the ABN is registered, from a date before the invoice.

What each field on ABN Lookup tells you

A record on ABN Lookup has a handful of fields. What each one means, and what to compare it with on the invoice:(ABR: ABN Lookup)

The fields on an ABN Lookup record, and what to compare with the supplier's invoice
Field	What it says	Compare it with
Entity name	What it says: The legal name of the business behind the ABN: a company, a person, a partnership or a trust.	Compare it with: The name on the invoice, or the business it trades as.
ABN status	What it says: Active from a date, or cancelled from a date.	Compare it with: The invoice date: the ABN should be active on it.
Entity type	What it says: Company, sole trader, trust, partnership and so on.	Compare it with: Whether it fits who you think you're dealing with.
Goods & Services Tax (GST)	What it says: Registered from a date, or not currently registered.	Compare it with: Whether the invoice charges GST at all.
Main business location	What it says: The state and postcode.	Compare it with: Where the supplier says it is.
Business name(s)	What it says: The names the business is registered to trade under.	Compare it with: The name on the invoice, when it isn't the entity name.

Entity name or business name?

An invoice usually carries the name a business trades under, which is often not its legal name. A company called something like a family trust can trade as a plumbing business, and both names sit on the same ABN record: the entity name at the top, the business names further down. A name on the invoice that appears nowhere on the record is worth a phone call to a number you already have for the supplier.(ABR: ABN Lookup)

Older records can also list trading names. The ABR stopped collecting and updating trading names in May 2012, and businesses now register their business names with ASIC, so a trading name on ABN Lookup may be out of date.(ABR: ABN Lookup)

The check digits

An ABN is 11 digits: a nine-digit identifier with two check digits in front, worked out with a modulus 89 calculation the ABR publishes. Subtract 1 from the first digit, multiply each of the 11 digits by its weighting (10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19), add the results, and divide by 89. A remainder of zero means the number is a well-formed ABN. The ABR's own example, worked through:(ABR: Format of the ABN)

ABN 51 824 753 556(5 − 1) × 10 + 1 × 1 + 8 × 3 + 2 × 5 + 4 × 7 + 7 × 9  + 5 × 11 + 3 × 13 + 5 × 15 + 5 × 17 + 6 × 19= 40 + 1 + 24 + 10 + 28 + 63 + 55 + 39 + 75 + 85 + 114 = 534534 ÷ 89 = 6, remainder 0

The checker at the top of this page runs that calculation in your browser. A number that passes is well formed, not necessarily registered, active or the supplier's: only ABN Lookup can say that. A number that fails isn't an ABN at all. On a scanned or photographed invoice that is most often a misread or mistyped digit, so compare it against the original before drawing any conclusion.(ABR: Format of the ABN)

Signs worth a question before you pay

None of these proves anything on its own, and most have an innocent explanation. Each is worth asking the supplier about, on a number you already have for them, before the money goes:

The ABN is cancelled, or became active only after the invoice date.
The invoice charges GST but the ABN isn't registered for GST, or wasn't on the invoice date. The ATO suggests checking a supplier's GST registration on ABN Lookup when you claim GST credits.(ATO: When you can claim a GST credit; ABR: ABN Lookup)
The name on the invoice appears nowhere on the ABN's record.
A supplier you've paid before sends an invoice with a different ABN from the last one.
The number fails the check digits, or has ten or twelve digits.
There's no ABN on the invoice at all.

When a supplier gives you no ABN

If a supplier doesn't give you their ABN and the total payment for the goods and services is more than $75 excluding GST, the ATO says you generally withhold tax at the top rate from the payment and pay it to the ATO. There are payments you don't have to withhold from, and a supplier who doesn't need to quote an ABN can give you a written statement saying why. You still need records showing why you didn't withhold.(ATO: Withholding if ABN is not provided)

If the supplier has applied for an ABN, you can agree to hold the payment until they've quoted it, but the ATO says you must not pay in full on the understanding that an ABN will come later. When you do withhold, you give the supplier a payment summary and keep those payments' records separately, because you can't claim a GST credit for them.(ATO: Withholding if ABN is not provided)

What to do when a check fails

Work from the likeliest explanation to the least likely:

Re-read the ABN on the original invoice. A misread digit on a scan, or a typo when it was keyed in, is the commonest cause.
Ask the supplier to confirm their ABN in writing, using contact details you already hold rather than ones printed on the invoice in question.
If GST is charged and the ABN isn't registered for GST, ask for a corrected invoice before you pay. An invoice with incorrect information isn't a valid tax invoice, and the ATO says to ask the supplier to replace it.(ATO: When you can claim a GST credit)
If no ABN comes, read the ATO's page on withholding before you pay anything over $75 excluding GST.(ATO: Withholding if ABN is not provided)

Payments to contractors: TPAR

If your business is mainly in building and construction and you pay contractors or subcontractors for building and construction services, you generally have to report those payments to the ATO each year in a taxable payments annual report, due by 28 August. Having each contractor's ABN right on your records as you go saves a scramble when the report is due.(ATO: Taxable payments annual report (TPAR); ATO: Building and construction services (TPAR))

What CostCode checks

CostCode's free invoice check reads one invoice and, where GST is charged, checks that an ABN is printed on it. When the ABN it reads fails the check digits, it asks you to check the original rather than calling the supplier out, because a misread digit looks exactly the same. With a free account, the same check runs on every invoice you upload: a tax invoice with no ABN printed is held with the evidence.

CostCode doesn't look the ABN up on ABN Lookup, and doesn't check that the ABN belongs to the business named on the invoice. Do that yourself for any supplier you haven't paid before.

Questions

Is ABN Lookup free?

Yes. It is the Australian Business Register's public search and needs no login.(ABR: ABN Lookup)

How do I check if an ABN is active?

Search it on ABN Lookup and read the ABN status: active from a date, or cancelled from a date. Compare that date with the invoice date.(ABR: ABN Lookup)

How do I know if a supplier is registered for GST?

Search their ABN on ABN Lookup. It shows whether the ABN is registered for GST and from what date.(ABR: ABN Lookup)

Does a number that passes the check digits mean the ABN is real?

No. It means the number is well formed. Only ABN Lookup shows whether it's registered, active and whose it is.(ABR: Format of the ABN; ABR: ABN Lookup)

What if a supplier won't give me an ABN?

For a payment over $75 excluding GST you generally have to withhold tax at the top rate from the payment unless an exception applies. Read the ATO's page on withholding when an ABN is not provided.(ATO: Withholding if ABN is not provided)

Sources

General information, not tax, legal or financial advice. The rules have exceptions and change over time: the official pages above are the authority, and your accountant or the ATO can tell you how they apply to your business.