SSN Regex Python Validator

What is SSN Regex?

A Social Security Number (SSN) in the U.S. follows the standard format:

XXX-XX-XXXX, where:

• XXX: Area number (3 digits)

• XX: Group number (2 digits)

• XXXX: Serial number (4 digits)

This format ensures structured identification for tax and legal purposes. Using regex helps validate whether an input string follows this format strictly.

SSN Regex Pattern

The typical regex pattern to validate a properly formatted SSN is:

^\d{3}-\d{2}-\d{4}$

Breakdown:

• ^\d{3} → Three digits at the start

• - → First hyphen separator

• \d{2} → Two digits

• - → Second hyphen

• \d{4}$ → Four digits at the end

This ensures strict format matching like 123-45-6789.

Python Example Code

import re

def is_valid_ssn(ssn):
    pattern = re.compile(r'^\d{3}-\d{2}-\d{4}$')
    return bool(pattern.fullmatch(ssn))

# Test Cases
print(is_valid_ssn("123-45-6789"))  # True
print(is_valid_ssn("123456789"))    # False
print(is_valid_ssn("12-345-6789"))  # False

Test regex variations with the Python Regex Tester.

Use Cases

• User Identity Verification: Ensure accurate SSN input during user registration or onboarding.

• Data Cleaning: Detect and correct improperly formatted SSNs in databases.

• Security & Compliance: Verify SSN format before transmitting sensitive data.

You can combine this with:

• Email Regex Python Validator for account verification

• IP Address Regex Python Validator for system security

• URL Regex Python Validator to secure form input fields

Regex Metacharacters Used

• ^ : Anchors the start of the string

• \d : Matches any digit (0–9)

• {n} : Matches exactly n digits

• - : Matches literal hyphens in SSNs

• $ : Anchors the end of the string

Pro Tips

• Always anchor patterns with ^ and $ to avoid partial matches.

• Preprocess user input to trim whitespaces before validation.

• You can extend validation to exclude invalid combinations (like 000 or 666) using advanced regex or logic.

• Avoid storing plain SSNs—encrypt them after validation.

• Use Python Regex Tester to experiment before deploying.

• Combine with Date Regex Python Validator if SSNs are part of a larger structured document.