Interest Rate (APR / APY) Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching interest rate (apr / apy), ported and verified for PHP. 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 PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Interest Rate (APR / APY)
// ReDoS-safe | RegexVault — Finance > Currency & Money

define('INTEREST_RATE_APR_APY_PATTERN', '/^(?:0(?:\.[0-9]{1,4})?|[1-9][0-9]{0,4}(?:\.[0-9]{1,4})?)%?$/');

function validate_interest_rate_apr_apy(string $input): bool {
    return (bool) preg_match(INTEREST_RATE_APR_APY_PATTERN, $input);
}

// Example
var_dump(validate_interest_rate_apr_apy("0")); // bool(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 PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. 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

Does not impose an upper bound to accommodate DeFi yields, payday loan rates, or penalty rates that can exceed 100%. Add a domain-specific cap at the application level. APR and APY differ when compounding is applied.