Pattern

Regex for ISO 8601 date (YYYY-MM-DD)

The international date format.

The pattern

^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$

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What it matches

2024-01-15
2026-12-31
1999-02-28

What it doesn't match

2024-13-01
2024-00-15
24-01-15
2024-1-15

Notes & gotchas

Validates structure but not semantic correctness (accepts Feb 31). After regex passes, parse with a date library to check the date actually exists.

Code in your language

Use the explainer's Code tab to generate ready-to-paste snippets in JavaScript, Python, Java, .NET, Go, Ruby, and PHP for this pattern.

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About this pattern

Date and time formats vary enormously across regions and systems. The regex here validates structure only — a date like 2024-02-30 would pass format validation but isn't a real date. After regex passes, parse with your language's date library to confirm semantic validity.

Quick usage in different languages

Once you've validated a candidate value matches this pattern, you'll typically use it inside your application code. Each language has its own regex syntax:

JavaScript: new RegExp(pattern).test(value)
Python: re.match(pattern, value) with raw strings: r"pattern"
Java: Pattern.compile(pattern).matcher(value).matches()
C# / .NET: Regex.IsMatch(value, pattern)
Go: regexp.MustCompile(pattern).MatchString(value) — Go uses RE2 so some advanced features aren't available
Ruby: value =~ /pattern/ or pattern.match?(value)
PHP: preg_match('/pattern/', $value)

The explainer's Code tab generates these for any pattern you paste — including the right escaping and idioms for each language.

Common pitfalls

Anchors matter. If the pattern uses ^ and $ it expects the entire input to match. To find this pattern inside a longer text, remove the anchors and use the /g flag.
Case sensitivity. Letter ranges like [A-Z] only match uppercase. Use the i flag or [A-Za-z] for case-insensitive matching.
Escape user input. If you're building a regex from a string variable, escape regex metacharacters first to avoid bugs or injection.
Performance. For this specific pattern the risk is low, but be cautious of nested quantifiers when adapting it — they can cause exponential backtracking on adversarial input.