UK National Insurance Number Regex for Java

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching uk national insurance number, ported and verified for Java. 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 Java project — whether you're validating in a Spring Boot controller, a Jakarta EE service, or a standalone utility class.

Java Implementation

// UK National Insurance Number
// ReDoS-safe | RegexVault — Finance > Tax & Registration

import java.util.regex.Pattern;

public class UkNationalInsuranceNumberValidator {
    private static final Pattern PATTERN =
        Pattern.compile("^(?:QQ|(?!BG|GB|NK|KN|TN|NT|ZZ)[A-CEGHJ-NOPR-TW-Z]{1}[A-CEGHJ-NPR-TW-Z]{1})[0-9]{6}[A-D]$");

    public static boolean validate(String input) {
        return PATTERN.matcher(input).matches();
    }

    // Example
    public static void main(String[] args) {
        System.out.println(validate("AB123456C")); // true
    }
}

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Tax & Registration category and carries a ReDoS-safe certification. That matters for Java developers because critical in Java applications since the JVM regex engine uses backtracking and is susceptible to ReDoS without careful pattern design. 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

Invalid prefixes: BG, GB, NK, KN, TN, NT, ZZ. Second letter excludes D, F, I, Q, U, V. First letter also excludes D, F, I, Q, U, V plus O. Suffix must be A-D (not E onward).