Check ABN
Instantly validate Australian Business Numbers (ABNs) using the official modulus 89 checksum published by ABN Lookup. The result checks number structure, not registration status or business identity.
Supports all 11-digit ABN formats. Processing happens entirely in your browser.
Enter ABN
Enter an 11-digit ABN with or without spaces
Example ABNs for testing:
How to Use the ABN Checker
Enter the ABN
Type or paste the 11-digit Australian Business Number into the input field. Spaces and dashes are automatically removed. You can also click an example ABN to test.
Check the ABN
Click 'Check ABN' or press Enter. The tool validates the checksum using the ATO's official modulus 89 algorithm in milliseconds.
View the result
A valid result shows the formatted number, weighted sum, and checksum status. It does not prove that the ABN is registered, active, or belongs to a named entity.
How ABN Validation Works
weighted_sum mod 89 = 0 → validABN validation uses the ATO's official modulus 89 algorithm with weighted checksum verification.
Step 1: Subtract 1 from the first digit of the ABNStep 2: Multiply each digit by its weight [10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19]Step 3: Sum all 11 weighted productsStep 4: If the sum divides evenly by 89, the ABN is validExample: validating ABN 53 004 085 616
This tool performs all validation client-side in your browser. No data is sent to any server.
ABN Structure
| Position | Digits | Description |
|---|---|---|
| 1-2 | 2 | Check digits tested by the modulus 89 calculation |
| 3-11 | 9 | Entity identifier; for an Australian company, this is its nine-digit ACN |
ABNs are always 11 digits and cannot begin with 0.
What an ABN Checksum Can — and Cannot — Verify
A checksum is a fast typing-error screen. It is useful before copying an ABN onto an invoice, supplier record, reimbursement form or accounting import because a missing, duplicated or changed digit will usually fail the modulus 89 test. The calculation is deterministic, so the same eleven digits always produce the same answer and can be checked without sending business data to a third party.
A successful checksum is not evidence that a business exists or that the person who supplied the number controls it. Some mathematically valid combinations may never have been issued, an issued ABN may later be cancelled, and a typing error can occasionally turn one valid number into another valid number. The checksum also cannot reveal a legal name, business name, entity type, address, GST registration or entitlement to quote the ABN.
For a reliable supplier or customer check, use this page first to catch formatting and checksum errors, then open the official ABN Lookup record. Compare the displayed legal or trading name with the documents you received, confirm that the ABN status is active, and check the GST registration dates when GST treatment matters. Keep the registry result with your onboarding evidence when your organisation's process requires it. An ACN and an ABN are related for Australian companies, but they are not interchangeable: an ACN has nine digits, while an ABN has eleven.
Official ABN Sources and Verification Scope
This validator implements the exact 11-digit weighting method documented by the Australian Business Register. Passing the checksum means the number is structurally possible. It does not confirm that the ABN was issued, remains active, has GST registration, or belongs to the organisation that supplied it.
For registration status, legal name, entity type, trading names and GST details, continue to the official government registry after checking the number for typing errors here.
Frequently Asked Questions
What is an ABN?
An ABN (Australian Business Number) is a unique 11-digit identifier issued to all entities registered in the Australian Business Register (ABR). It was introduced on 1 July 2000 as part of the New Tax System. Every business operating in Australia needs an ABN for tax purposes, invoicing, and dealings with other businesses and government agencies.
How does ABN validation work?
ABN validation uses the ATO's official modulus 89 algorithm. First, subtract 1 from the first digit. Then multiply each of the 11 digits by their respective weighting factors (10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19). Sum all 11 products and divide by 89. If the remainder is zero, the ABN is mathematically valid. This checks the structural integrity of the number but does not verify the business is currently active.
Does this tool check if a business is active?
No, this tool performs structural validation only, checking that the ABN format and checksum are mathematically correct. To verify whether a business is currently registered and active, use the official ABN Lookup at abr.business.gov.au. Our tool is useful for quickly catching typos and formatting errors before looking up details.
What is the difference between an ABN and an ACN?
An ABN (Australian Business Number) is an 11-digit identifier for all business entities, while an ACN (Australian Company Number) is a 9-digit number specifically for companies registered under the Corporations Act 2001. A company's ABN is typically derived from its ACN by prefixing two check digits. Sole traders, partnerships, and trusts have ABNs but not ACNs.
Is my data safe when using this tool?
Yes, completely. All ABN validation is performed entirely in your browser using JavaScript. No data is sent to any server, stored, or transmitted. You can verify this by using the tool in your browser's offline mode after the page has loaded. No data is logged whatsoever.
Privacy Notice
This ABN checker runs entirely in your web browser. Your data is never uploaded, stored, or processed on any server. All validation uses standard browser JavaScript and the ATO's published modulus 89 algorithm. You can safely use this tool with real ABNs -- your data never leaves your device.
Published by Kalcify · Last updated
Calculators are built against primary sources — government tax authorities (IRS, HMRC, CRA, ATO) for finance and the World Health Organization for health metrics. Updated when rates or rules change. View methodology and data sources.
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