Australian Business Number (ABN) Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching australian business number (abn), ported and verified for PHP. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Australian Business Number (ABN)
// ReDoS-safe | RegexVault — Finance > Tax & Registration

define('AUSTRALIAN_BUSINESS_NUMBER_ABN_PATTERN', '/^[0-9]{2}\s?[0-9]{3}\s?[0-9]{3}\s?[0-9]{3}$/');

function validate_australian_business_number_abn(string $input): bool {
    return (bool) preg_match(AUSTRALIAN_BUSINESS_NUMBER_ABN_PATTERN, $input);
}

// Example
var_dump(validate_australian_business_number_abn("51824753556")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Tax & Registration category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Format validation only. ABN checksum: subtract 1 from first digit, multiply each by weight (10,1,3,5,7,9,11,13,15,17,19), sum, divide by 89, remainder must be 0. Validate via ABR (Australian Business Register) for active status.