Australian Business Number (ABN) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching australian business number (abn), ported and verified for Python. 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 Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# Australian Business Number (ABN)
# ReDoS-safe | RegexVault — Finance > Tax & Registration

import re

australian_business_number_abn_pattern = re.compile(r'^[0-9]{2}\s?[0-9]{3}\s?[0-9]{3}\s?[0-9]{3}$')

def validate_australian_business_number_abn(value: str) -> bool:
    return bool(australian_business_number_abn_pattern.fullmatch(value))

# Example
print(validate_australian_business_number_abn("51824753556"))  # 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 Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. 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.