US Employer Identification Number (EIN) Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching us employer identification number (ein), 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
// US Employer Identification Number (EIN)
// ReDoS-safe | RegexVault — Finance > Tax & Registration

define('US_EMPLOYER_IDENTIFICATION_NUMBER_EIN_PATTERN', '/^(?:0[1-9]|[1-9][0-9])-[0-9]{7}$/');

function validate_us_employer_identification_number_ein(string $input): bool {
    return (bool) preg_match(US_EMPLOYER_IDENTIFICATION_NUMBER_EIN_PATTERN, $input);
}

// Example
var_dump(validate_us_employer_identification_number_ein("12-3456789")); // 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

The first two digits identify the IRS campus that issued the EIN. 00 is not a valid prefix. EINs are the business equivalent of SSNs. Used on W-2, 1099, and other tax forms.