ABN Lookup & Validator
Free ABN lookup and validation tool. Enter any 11-digit Australian Business Number and the ATO modulus 89 checksum is verified in your browser, which tells you the number is well formed. Status, entity name, entity type and GST registration are read from the Australian Business Register, which is a live lookup: it is rate limited and it can be unreachable, and when that happens the tool reports the checksum result only rather than implying the business is active. A cancelled ABN passes the checksum exactly as an active one does, so the two answers are not interchangeable.
Look up an ABN
ABREnter the 11-digit ABN to validate and look up
Enter an ABN to validate and look up
We'll check the format, then fetch the entity details from the Australian Business Register and tell you if the register does not answer
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About Australian Business Numbers
An ABN is a unique 11-digit identifier issued by the Australian Business Register (ABR). Every business operating in Australia needs one. It's used on invoices, tax returns, and when interacting with government agencies.
ABN format and structure
An ABN consists of 11 digits, typically displayed as XX XXX XXX XXX. The leading two digits are check digits, computed from the remaining nine digits using a modulus-89 weighted checksum so the format itself can be validated without contacting the registry. For companies, the last nine digits are the ACN (Australian Company Number).
Why validate ABNs?
Validating ABNs on invoices and supplier records helps you avoid paying incorrect entities, ensures you can claim GST credits correctly, and protects against fraudulent invoices. Under Australian tax law, if a supplier doesn't quote a valid ABN on an invoice of $75 or more (excluding GST), you must withhold 47% tax from the payment. Once you've confirmed a supplier's ABN, create a compliant document with the GST invoice generator.
How to apply for an ABN
Applying for an ABN is free, and the only official channel is the Australian Business Register (ABR), the government registry administered alongside the ATO. The online application at abr.gov.au takes around 10 to 15 minutes. You'll need your tax file number, your business structure (sole trader, partnership, company or trust), a short description of your main business activity, and your contact details. Companies must register with ASIC and receive their ACN first, because a company's ABN is built from its ACN.
Most successful applicants receive their ABN immediately. If the ABR needs to confirm your identity or review your entitlement, processing can take up to 20 business days. To be entitled to an ABN you must be carrying on (or starting) an enterprise in Australia: employees working under a TFN don't need one, and quoting an ABN for what is really employee work can cause problems at tax time.
Watch out for paid ABN lodgement websites
A number of private websites charge $50 to $100 or more to lodge the same application on your behalf. They often advertise above the official site in search results and look official, but they are not government services, and paying them gets you nothing you can't do yourself for free in a few minutes. Before entering any details, check the address bar: the official application lives on a .gov.au domain. Registered tax and BAS agents can legitimately apply for you as part of broader services, but the ABN itself never costs anything.
ABN vs ACN
An ABN identifies any business entity for tax purposes: sole traders, partnerships, companies and trusts all quote one on invoices and activity statements. An ACN is a 9-digit number ASIC issues only to registered companies, and a company's 11-digit ABN is its ACN with two check digits added in front. For plain-English explanations, read the ABN definition and the ACN definition, or browse the full Australian small business glossary.
Frequently asked questions
What is an ABN?
An Australian Business Number (ABN) is a unique 11-digit number that identifies your business to the government and community. It's used for tax and business purposes, including on invoices, when claiming GST credits, and when dealing with other businesses.
How does ABN validation work?
ABN validation uses a checksum algorithm (modulus 89). The first digit is subtracted by 1, then each digit is multiplied by a specific weight (10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19). If the sum of all weighted digits divides evenly by 89, the ABN is valid.
Do I need an ABN?
You need an ABN if you're carrying on a business in Australia. Sole traders, partnerships, companies, and trusts all need an ABN. It's free to apply via the Australian Business Register (ABR). If a supplier doesn't quote an ABN on an invoice of $75 or more (excluding GST), the payer must withhold 47% (the top marginal tax rate) from the payment and remit it to the ATO.
What's the difference between ABN and ACN?
An ABN (Australian Business Number) is an 11-digit number for all business entities: sole traders, partnerships, companies, and trusts. An ACN (Australian Company Number) is a 9-digit number issued by ASIC specifically to registered companies. Companies have both, and a company's ABN is simply its ACN with two check digits added in front.
How much does it cost to apply for an ABN?
Nothing. Applying through the Australian Business Register (abr.gov.au) is free and takes around 10 to 15 minutes online. Most applicants receive their ABN immediately. Private websites that charge a fee to lodge the same application are not government services; the official application is always free.
Can I look up a business by ABN?
Yes, you can use the Australian Business Register (ABR) at abr.business.gov.au to look up any ABN. It will show the entity name, type, GST registration status, and more. Our tool validates the format and also queries the ABR for entity details when available.
Sources & methodology
How we calculate this
This tool first validates the 11-digit ABN format in your browser using the Australian Business Register's modulus-89 weighted checksum (no rates or financial-year figures are applied), then queries the ABR's public registry for the entity name, type, ABN status and GST registration. If the register does not answer, we say so and show you the checksum result on its own, because a cancelled ABN passes the checksum exactly as an active one does. Only the digits you look up are sent to the ABR.
Authoritative sources
Reviewed by Bishal Shrestha, Founder of OneBookPlus, 10+ years building tools with Australian tax-agent and BAS-agent practices. Page last reviewed and updated: .
Disclaimer: This tool provides estimates only and is not professional advice. For decisions that affect your tax, finances, or compliance position, consult a registered professional.
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