Regex for 24-Hour Time (HH:MM)

Read it left to right. Each piece below matches one part of the input:

• ^ Start of the string.
• (?:[01]\d|2[0-3]) The hour: 00–19, or 20–23. Two digits are required.
• : A colon.
• [0-5]\d Minutes from 00 to 59.
• (?::[0-5]\d)? Optionally a colon and seconds from 00 to 59.
• $ End of the string: no AM/PM suffix.

The whole input must match, from the first character to the last. Every row below is checked against the pattern by our automated test suite before each release.

Three common variations:

• 24-hour, hour may be one digit (9:30): ^(?:[01]?\d|2[0-3]):[0-5]\d$
• 12-hour with AM/PM (9:30 pm): ^(?:0?[1-9]|1[0-2]):[0-5]\d\s?[AaPp][Mm]$
• With milliseconds (13:45:30.250): ^(?:[01]\d|2[0-3]):[0-5]\d:[0-5]\d\.\d{3}$

Note the 12-hour clock runs from 1 to 12, so 0?[1-9]|1[0-2] replaces the 24-hour alternatives. Normalize to 24-hour time before storing; it avoids the "is 12:00 AM midnight or noon?" question entirely.

Not on its own. A time without a date and a time zone is a wall-clock reading, and some readings do not exist or happen twice: when clocks spring forward for daylight saving time, 02:30 does not occur in many zones, and in autumn 01:30 happens twice. If you combine a date, a time and a zone, use a time-zone-aware library (Temporal in modern JavaScript, zoneinfo in Python, time.LoadLocation in Go) to resolve it.

For schedules that repeat, such as "every weekday at 09:30", a cron expression is the better format: build one with the cron expression generator.

The pattern is translated for each engine rather than pasted as is: named groups, anchors, escapes, shorthand classes and flags are adjusted so each snippet behaves as closely to the JavaScript version as its engine allows. Differences that remain (Go's RE2 has no lookarounds or backreferences, for example) are called out under each one. The Code tab in the tester above also exports Dart, and updates as you edit the pattern.

JavaScript and TypeScript

const regex = /^(?:[01]\d|2[0-3]):[0-5]\d(?::[0-5]\d)?$/;

function isValid(value) {
  return regex.test(value);
}

console.log(isValid("00:00"));

Python

import re

pattern = re.compile(r"^(?:[01][0-9]|2[0-3]):[0-5][0-9](?::[0-5][0-9])?\Z")

def is_valid(value: str) -> bool:
    return pattern.search(value) is not None

print(is_valid("00:00"))

• \d and \w are written as [0-9] and [A-Za-z0-9_] because in Python they also match digits and letters from other scripts.
• JavaScript's $ only matches at the very end of the string. Python's $ also matches before a trailing newline, so the pattern uses \Z instead.

Go

package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`^(?:[01]\d|2[0-3]):[0-5]\d(?::[0-5]\d)?$`)
	fmt.Println(re.MatchString("00:00"))
}

C#

using System;
using System.Text.RegularExpressions;

// The timeout stops a pathological input from hanging the thread (ReDoS).
var regex = new Regex(@"^(?:[01][0-9]|2[0-3]):[0-5][0-9](?::[0-5][0-9])?\z", RegexOptions.None, TimeSpan.FromSeconds(1));
Console.WriteLine(regex.IsMatch("00:00"));

• \d and \w are written as [0-9] and [A-Za-z0-9_] because in .NET they also match digits and letters from other scripts.
• JavaScript's $ only matches at the very end of the string. .NET's $ also matches before a trailing newline, so the pattern uses \z instead.

PHP

<?php

$pattern = '/^(?:[01]\d|2[0-3]):[0-5]\d(?::[0-5]\d)?$/D';

function isValid(string $value, string $pattern): bool
{
    return preg_match($pattern, $value) === 1;
}

var_dump(isValid('00:00', $pattern));

• The D modifier makes $ match only at the very end, like JavaScript (PCRE's $ also matches before a trailing newline).

• Regex for Dates in yyyy-mm-dd Format: ISO 8601 calendar dates: four-digit year, month 01–12, day 01–31.
• Regex for Numbers Only: Digits only, plus variants for signs, decimals and thousands separators.
• Regex for Semantic Versioning (SemVer): major.minor.patch with optional prerelease and build metadata, per semver.org.
• Regex for Hex Color Codes: CSS hex colors in 3, 4, 6 or 8 digits with a leading hash.

Browse all 25 patterns in the regex pattern library, or build your own in the regex tester.