Japanese Imperial Era Year (Reiwa/Heisei/Showa) Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching japanese imperial era year (reiwa/heisei/showa), ported and verified for PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. 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
// Japanese Imperial Era Year (Reiwa/Heisei/Showa)
// ReDoS-safe | RegexVault — Localization > Date Formats

define('JAPANESE_IMPERIAL_ERA_YEAR_REIWAHEISEISHOWA_PATTERN', '/^(?:(令和|R)((?:[1-9]|[1-9][0-9]))|(平成|H)((?:[1-9]|[12][0-9]|3[01]))|(昭和|S)((?:[1-9]|[12][0-9]|3[0-9]|6[0-4])))年(0?[1-9]|1[0-2])月(0?[1-9]|[12][0-9]|3[01])日$/');

function validate_japanese_imperial_era_year_reiwaheiseishowa(string $input): bool {
    return (bool) preg_match(JAPANESE_IMPERIAL_ERA_YEAR_REIWAHEISEISHOWA_PATTERN, $input);
}

// Example
var_dump(validate_japanese_imperial_era_year_reiwaheiseishowa("令和6年1月15日")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Date Formats 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

Era limits: 令和/Reiwa started May 1, 2019 (max year currently ~6). 平成/Heisei: 1-31 (1989-2019). 昭和/Showa: 1-64 (1926-1989). Meiji and Taisho are pre-1926 and excluded here. Convert to Gregorian for storage.