Interest Rate (APR / APY) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching interest rate (apr / apy), ported and verified for JavaScript. 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 JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

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

const interestRateAprApyRegex = /^(?:0(?:\.[0-9]{1,4})?|[1-9][0-9]{0,4}(?:\.[0-9]{1,4})?)%?$/;

function validateInterestRateAprApy(input: string): boolean {
  return interestRateAprApyRegex.test(input);
}

// Example
console.log(validateInterestRateAprApy("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 JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. 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.