Check ABN
Instantly validate Australian Business Numbers (ABNs) using the official ATO checksum algorithm. Detect entity type and verify correct formatting.
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 ABN shows the formatted number, entity type, and checksum status. An invalid ABN displays a specific error message explaining what's wrong.
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 (also indicate entity type) |
| 3-9 | 7 | Unique identifier (derived from ACN for companies) |
| 10-11 | 2 | Additional identifier digits |
ABNs are always 11 digits and cannot begin with 0.
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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