Pattern

Regex for ISO 8601 duration

Duration like P1Y2M3DT4H5M6S.

The ISO 8601 duration regex is ^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$

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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)
`P`	literal text “P”
`(?!`	start of a negative lookahead — NOT followed by
`$`	end of string (or line in multiline mode)
`)`	end of group
`(`	start of a capturing group
`\d+`	one or more: digit (0–9)
`Y`	literal text “Y”
`)?`	end of group, optional (zero or one)
`(`	start of a capturing group
`\d+`	one or more: digit (0–9)
`M`	literal text “M”
`)?`	end of group, optional (zero or one)
`(`	start of a capturing group
`\d+`	one or more: digit (0–9)
`D`	literal text “D”
`)?`	end of group, optional (zero or one)
`(`	start of a capturing group
`T`	literal text “T”
`(`	start of a capturing group
`\d+`	one or more: digit (0–9)
`H`	literal text “H”
`)?`	end of group, optional (zero or one)
`(`	start of a capturing group
`\d+`	one or more: digit (0–9)
`M`	literal text “M”
`)?`	end of group, optional (zero or one)
`(`	start of a capturing group
`\d+`	one or more: digit (0–9)
`(`	start of a capturing group
`\.`	literal “.”
`\d+`	one or more: digit (0–9)
`)?`	end of group, optional (zero or one)
`S`	literal text “S”
`)?`	end of group, optional (zero or one)
`)?`	end of group, optional (zero or one)
`$`	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: /^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$/.test(value)
Python: re.match(r"^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$", value)
Java: Pattern.compile("^P(?!$)(\\d+Y)?(\\d+M)?(\\d+D)?(T(\\d+H)?(\\d+M)?(\\d+(\\.\\d+)?S)?)?$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$")
Go: regexp.MustCompile(`^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$`).MatchString(value)
Ruby: /^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$/.match?(value)
PHP: preg_match('~^P(?!$)(\d+Y)?(\d+M)?(\d+D)?(T(\d+H)?(\d+M)?(\d+(\.\d+)?S)?)?$~', $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 duration 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.

Related patterns

More patterns in the Date & time category: