IBAN (UK — GB) Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching iban (uk — gb), 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

// IBAN (UK — GB)
// ReDoS-safe | RegexVault — Finance > Bank Identifiers

const ibanUkGbRegex = /^GB[0-9]{2}[A-Z]{4}[0-9]{14}$/;

function validateIbanUkGb(input: string): boolean {
  return ibanUkGbRegex.test(input);
}

// Example
console.log(validateIbanUkGb("GB29NWBK60161331926819")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Bank Identifiers 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

UK IBANs are always 22 characters. The 4-char bank code is a subset of the BIC. UK personal accounts typically have 8-digit account numbers. Building society accounts may differ.