12-Hour Time (H:MM AM/PM) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching 12-hour time (h:mm am/pm), ported and verified for JavaScript. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// 12-Hour Time (H:MM AM/PM)
// ReDoS-safe | RegexVault — Localization > Time Formats

const 12hourTimeHmmAmpmRegex = /^(1[0-2]|0?[1-9]):([0-5][0-9])(?::([0-5][0-9]))?\s?(AM|PM|am|pm|Am|Pm)$/i;

function validate12hourTimeHmmAmpm(input: string): boolean {
  return 12hourTimeHmmAmpmRegex.test(input);
}

// Example
console.log(validate12hourTimeHmmAmpm("12:30 PM")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Time Formats category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. 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

12:00 AM = midnight, 12:00 PM = noon — the most commonly confused values. 12-hour format is standard in US, UK, Australia, and parts of Asia. Many others use 24-hour exclusively.