Credit Card Validation Regex (MasterCard)

Validate MasterCard credit card numbers starting with 51-55 and having 16 digits using regex pattern.

Pattern Breakdown

^5[1-5][0-9]{14}$

Components

Character Classes

• 5 - Literal 5 (MasterCard starts with 5)
• [1-5] - Second digit: 1, 2, 3, 4, or 5 (range 51-55)
• [0-9] - Any digit 0-9
• {14} - Quantifier: exactly 14 occurrences

Examples

Valid:

• 5111111111111111 (starts with 51)
• 5211111111111111 (starts with 52)
• 5311111111111111 (starts with 53)
• 5411111111111111 (starts with 54)
• 5511111111111111 (starts with 55)

Invalid:

• 4111111111111111 (starts with 4, Visa)
• 5611111111111111 (starts with 56, outside range)
• 5011111111111111 (starts with 50, outside range)
• 511111111111111 (only 15 digits)
• 5-1111-1111-1111-1111 (contains formatting)

Implementation

JavaScript

const mastercardRegex = /^5[1-5][0-9]{14}$/;
mastercardRegex.test('5111111111111111'); // true
mastercardRegex.test('5511111111111111'); // true
mastercardRegex.test('4111111111111111'); // false (Visa)
mastercardRegex.test('5611111111111111'); // false (outside range)

// To handle formatted numbers, remove formatting first
const formatted = '5111-1111-1111-1111'.replace(/[-\s]/g, '');
mastercardRegex.test(formatted); // true

Python

import re
mastercard_regex = r'^5[1-5][0-9]{14}$'
bool(re.match(mastercard_regex, '5111111111111111'))  # True
bool(re.match(mastercard_regex, '5511111111111111'))  # True
bool(re.match(mastercard_regex, '4111111111111111'))  # False (Visa)

# To handle formatted numbers
formatted = '5111-1111-1111-1111'.replace('-', '').replace(' ', '')
bool(re.match(mastercard_regex, formatted))  # True

Go

mastercardRegex := regexp.MustCompile(`^5[1-5][0-9]{14}$`)
mastercardRegex.MatchString("5111111111111111") // true
mastercardRegex.MatchString("5511111111111111") // true
mastercardRegex.MatchString("4111111111111111") // false (Visa)

Limitations

1. No Luhn algorithm: Doesn't validate using Luhn checksum algorithm
2. No formatting: Doesn't accept formatted numbers (spaces, dashes)
3. Format only: Validates format, not actual card validity
4. No expiration/CVV: Doesn't validate expiration date or CVV
5. Security: Never store full card numbers, only last 4 digits
6. Note: MasterCard also issues cards starting with 2 (2-series), not covered by this pattern

When to Use

• Initial format validation
• Quick card type detection
• Client-side validation (first pass)
• When you need to identify MasterCard cards

For production, consider:

• Implementing Luhn algorithm for checksum validation
• Supporting 2-series MasterCard cards (starts with 2)
• Supporting formatted input (remove spaces/dashes)
• Using payment processing libraries (Stripe, PayPal, etc.)
• Never storing full card numbers
• Server-side validation (never trust client-side only)
• PCI DSS compliance requirements