Pattern

Regex for ISO 8601 week date

YYYY-Www-D format ISO week date.

The ISO 8601 week date regex is ^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$

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What it matches

2024-W01-1
2024-W23-4
2024-W53-7

What it doesn't match

2024-W54-1
2024-W01-0
2024W01-1

Notes & gotchas

ISO 8601 week date: year + W + week number (01-53) + day of week (1=Mon to 7=Sun). Less ambiguous for cross-year week reporting.

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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Token-by-token breakdown

Every part of the pattern, left to right:

Token	Meaning
`^`	start of string (or line in multiline mode)
`\d{4}`	exactly 4 times: digit (0–9)
`-W`	literal text “-W”
`(`	start of a capturing group
`0`	literal text “0”
`[1-9]`	any of: 1–9
`\|`	OR — try the alternative
`[1-4]`	any of: 1–4
`\d`	any digit (0–9)
`\|`	OR — try the alternative
`5`	literal text “5”
`[0-3]`	any of: 0–3
`)`	end of group
`-`	literal text “-”
`[1-7]`	any of: 1–7
`$`	end of string (or line in multiline mode)

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

This exact pattern — with the correct escaping and idioms for each language:

JavaScript: /^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$/.test(value)
Python: re.match(r"^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$", value)
Java: Pattern.compile("^\\d{4}-W(0[1-9]|[1-4]\\d|5[0-3])-[1-7]$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$")
Go: regexp.MustCompile(`^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$`).MatchString(value)
Ruby: /^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$/.match?(value)
PHP: preg_match('~^\d{4}-W(0[1-9]|[1-4]\d|5[0-3])-[1-7]$~', $value)

The explainer’s Code tab regenerates these for any pattern you paste, and the downloadable cheat sheet bundles the breakdown, all seven snippets, and the pitfalls below onto one printable page.

Common pitfalls

Anchored to the whole string. This pattern uses ^ and $, so it requires the entire input to match. To find it inside a longer text, drop the anchors and use the global (g) flag.
Escape it correctly per language. In Java and JavaScript strings each backslash must be doubled (\\d); in Python, Go, and C# use raw/verbatim strings so the backslashes survive.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the iso 8601 week date against a source of truth (database, API, or checksum) where it matters.

Standards & sources

This pattern is based on the following authoritative specification(s) and issuing authorities. Formats can change — always confirm against the primary source.

ISO 8601 — Date and time format

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