US Social Security Number (SSN) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching us social security number (ssn), 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

# US Social Security Number (SSN)
# ReDoS-safe | RegexVault — Finance > Tax & Registration

import re

us_social_security_number_ssn_pattern = re.compile(r'^(?!(?:000|666|9[0-9]{2})-)[0-9]{3}-(?!00-)[0-9]{2}-(?!0{4})[0-9]{4}$')

def validate_us_social_security_number_ssn(value: str) -> bool:
    return bool(us_social_security_number_ssn_pattern.fullmatch(value))

# Example
print(validate_us_social_security_number_ssn("123-45-6789"))  # 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

Invalid SSN ranges: 000-XX-XXXX (area 000), 666-XX-XXXX, 900-999-XX-XXXX. Group 00 and serial 0000 are also invalid. The pre-2011 geographic assignment pattern is no longer used.