Percentage Value Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching percentage value, ported and verified for Python. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# Percentage Value
# ReDoS-safe | RegexVault — Finance > Currency & Money

import re

percentage_value_pattern = re.compile(r'^-?(?:100(?:\.0{1,4})?|(?:[0-9]{1,2}(?:\.[0-9]{1,4})?))%?$')

def validate_percentage_value(value: str) -> bool:
    return bool(percentage_value_pattern.fullmatch(value))

# Example
print(validate_percentage_value("0"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Currency & Money category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Constrained to -100 to 100. For percentages that can exceed 100% (e.g., year-over-year growth), remove the upper bound: ^-?[0-9]+(?:\.[0-9]{1,4})?%?$ . The percent sign is optional for API input.