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Credit Card Validation Regex (American Express)

• CronOS Team
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Credit Card Validation Regex (American Express)

Validate American Express credit card numbers starting with 34 or 37 and having 15 digits using regex pattern.

Pattern Breakdown

regex
^3[47][0-9]{13}$

Components

ComponentDescriptionMatches
^Start anchorEnsures match from string start
3Amex prefixMust start with 3
[47]Second digitMust be 4 or 7 (34 or 37)
[0-9]{13}Remaining digitsExactly 13 more digits (15 total)
$End anchorEnsures match to string end

Character Classes

  • 3 - Literal 3 (Amex starts with 3)
  • [47] - Second digit: 4 or 7 (34 or 37)
  • [0-9] - Any digit 0-9
  • {13} - Quantifier: exactly 13 occurrences

Examples

Valid:

  • 341111111111111 (starts with 34, 15 digits)
  • 371111111111111 (starts with 37, 15 digits)
  • 340000000000000 (starts with 34)
  • 379999999999999 (starts with 37)

Invalid:

  • 4111111111111111 (starts with 4, Visa)
  • 351111111111111 (starts with 35, not Amex)
  • 34111111111111 (only 14 digits)
  • 3411111111111111 (16 digits)
  • 3-4111-1111-1111-111 (contains formatting)

Implementation

JavaScript

javascript
const amexRegex = /^3[47][0-9]{13}$/;
amexRegex.test('341111111111111'); // true
amexRegex.test('371111111111111'); // true
amexRegex.test('4111111111111111'); // false (Visa)
amexRegex.test('351111111111111'); // false (not Amex range)

// To handle formatted numbers, remove formatting first
const formatted = '3411-111111-11111'.replace(/[-\s]/g, '');
amexRegex.test(formatted); // true

Python

python
import re
amex_regex = r'^3[47][0-9]{13}$'
bool(re.match(amex_regex, '341111111111111'))  # True
bool(re.match(amex_regex, '371111111111111'))  # True
bool(re.match(amex_regex, '4111111111111111'))  # False (Visa)

# To handle formatted numbers
formatted = '3411-111111-11111'.replace('-', '').replace(' ', '')
bool(re.match(amex_regex, formatted))  # True

Go

go
amexRegex := regexp.MustCompile(`^3[47][0-9]{13}$`)
amexRegex.MatchString("341111111111111") // true
amexRegex.MatchString("371111111111111") // true
amexRegex.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. Fixed length: Only validates 15-digit Amex cards

When to Use

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

For production, consider:

  • Implementing Luhn algorithm for checksum validation
  • 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

Need to generate a regex pattern?

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