Percentage Validation Regex (0-100)

Validate percentage values from 0 to 100 with optional decimal places using regex pattern.

Pattern Breakdown

^(100|[1-9]?\d(\.\d\d?)?)$

Components

Detailed Breakdown

• 100 - Exact 100 (no decimals)
• [1-9]?\d - 0-99:
  • [1-9]? - Optional digit 1-9 (for 10-99)
  • \d - Any digit 0-9 (allows 0-9 and 10-99)
• (\.\d\d?)? - Optional decimal part:
  • \. - Literal dot
  • \d\d? - One or two decimal digits

Examples

Valid:

• 0
• 50
• 100
• 0.5
• 50.25
• 99.99
• 12.5

Invalid:

• 101 (exceeds 100)
• -5 (negative)
• 100.5 (100 cannot have decimals)
• 50.123 (too many decimal places)
• abc (non-numeric)

Implementation

JavaScript

const percentageRegex = /^(100|[1-9]?\d(\.\d\d?)?)$/;
percentageRegex.test('50'); // true
percentageRegex.test('100'); // true
percentageRegex.test('50.25'); // true
percentageRegex.test('0.5'); // true
percentageRegex.test('101'); // false (exceeds 100)
percentageRegex.test('100.5'); // false (100 cannot have decimals)

Python

import re
percentage_regex = r'^(100|[1-9]?\d(\.\d\d?)?)$'
bool(re.match(percentage_regex, '50'))  # True
bool(re.match(percentage_regex, '100'))  # True
bool(re.match(percentage_regex, '50.25'))  # True
bool(re.match(percentage_regex, '101'))  # False (exceeds 100)

Go

percentageRegex := regexp.MustCompile(`^(100|[1-9]?\d(\.\d\d?)?)$`)
percentageRegex.MatchString("50") // true
percentageRegex.MatchString("100") // true
percentageRegex.MatchString("50.25") // true
percentageRegex.MatchString("101") // false (exceeds 100)

Limitations

1. No percent sign: Doesn't include % symbol (add %? if needed)
2. Fixed range: Hard-coded 0-100 range
3. Decimal limit: Allows up to 2 decimal places
4. Format only: Validates format, not actual percentage value
5. No leading zeros: Accepts 00 (may want to prevent this)

When to Use

• Percentage input validation
• Progress indicators
• Discount/commission calculations
• When you need 0-100 range validation
• Form input validation for percentages

For production, consider:

• Adding percent sign support: ^(100|[1-9]?\d(\.\d\d?)?)%?$
• Supporting different ranges if needed
• Allowing more decimal places if required
• Normalizing input (remove % sign, etc.)
• Converting to decimal (divide by 100) for calculations