Mastercard Number Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching mastercard number, 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

// Mastercard Number
// ReDoS-safe | RegexVault — Finance > Card Numbers

const mastercardNumberRegex = /^(?:5[1-5][0-9]{14}|2(?:2[2-9][1-9]|[3-6][0-9]{2}|7[01][0-9]|720)[0-9]{12})$/;

function validateMastercardNumber(input: string): boolean {
  return mastercardNumberRegex.test(input);
}

// Example
console.log(validateMastercardNumber("5500005555555559")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Card Numbers 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

Mastercard expanded their BIN range in 2017 to include 2221-2720. The 51-55 range is the original BIN prefix. Always strip separators before matching.