Pattern

Regex for Percentage (0-100%)

Percentage value with optional decimals and % sign.

The Percentage (0-100%) regex is ^(100(\.0+)?|\d{1,2}(\.\d+)?)\s*%?$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^(100(\.0+)?|\d{1,2}(\.\d+)?)\s*%?$

Try in explainer → Download cheat sheet ↓

What it matches

0%
50
99.99%
100.00
25 %

What it doesn't match

101%
-5%
abc%

Notes & gotchas

Accepts 0 to 100 with optional decimals and optional % sign. For percentages that can exceed 100 (like growth rates), use a different pattern.

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.

Open in explainer →

Token-by-token breakdown

Every part of the pattern, left to right:

Token	Meaning
`^`	start of string (or line in multiline mode)
`(`	start of a capturing group
`100`	literal text “100”
`(`	start of a capturing group
`\.`	literal “.”
`0+`	one or more: the literal “0”
`)?`	end of group, optional (zero or one)
`\|`	OR — try the alternative
`\d{1,2}`	between 1 and 2 times: digit (0–9)
`(`	start of a capturing group
`\.`	literal “.”
`\d+`	one or more: digit (0–9)
`)?`	end of group, optional (zero or one)
`)`	end of group
`\s*`	zero or more: whitespace
`%?`	optional (zero or one): the literal “%”
`$`	end of string (or line in multiline mode)

About this pattern

Number patterns appear constantly in form validation, log parsing, and data extraction. Regex is great for matching the shape but limited for semantic checks (range validation, mathematical constraints).

Quick usage in different languages

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

JavaScript: /^(100(\.0+)?|\d{1,2}(\.\d+)?)\s*%?$/.test(value)
Python: re.match(r"^(100(\.0+)?|\d{1,2}(\.\d+)?)\s*%?$", value)
Java: Pattern.compile("^(100(\\.0+)?|\\d{1,2}(\\.\\d+)?)\\s*%?$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^(100(\.0+)?|\d{1,2}(\.\d+)?)\s*%?$")
Go: regexp.MustCompile(`^(100(\.0+)?|\d{1,2}(\.\d+)?)\s*%?$`).MatchString(value)
Ruby: /^(100(\.0+)?|\d{1,2}(\.\d+)?)\s*%?$/.match?(value)
PHP: preg_match('~^(100(\.0+)?|\d{1,2}(\.\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 percentage (0-100%) against a source of truth (database, API, or checksum) where it matters.

Related patterns

More patterns in the Numbers & text category: