How to test Credit Card numbers using Luhn’s algorithm

Almost all credit card numbers used are generated using Luhn’s algorithm. Luhn’s algorithm is a simple checksum formula to validate variety of numbers. We can use the same formula for checking whether a given credit card number may be valid or not.

This can be used as a good technique to validate the credit card number in your web application. I found a simple function which validates any given number according to Luhn’s formula and gives the result to be true or false. The function is implemented in PHP and the primary source of this function is here.

<?php
function is_valid_luhn($number) {
  settype($number, 'string');
  $sumTable = array(
    array(0,1,2,3,4,5,6,7,8,9),
    array(0,2,4,6,8,1,3,5,7,9));
  $sum = 0;
  $flip = 0;
  for ($i = strlen($number) - 1; $i >= 0; $i--) {
    $sum += $sumTable[$flip++ & 0x1][$number[$i]];
  }
  return $sum % 10 === 0;
}

This small function is very useful if you want to check the validity of the credit card number being provided before passing it to your payment mechanism.

Sample Credit Card Numbers for testing

When I implemented this in my code, I also wanted to have some sample credit card numbers to test this. Sample credit card numbers are also very useful in many cases so here are the credit card numbers that I found.

Credit Card Type Credit Card Number
American Express 378282246310005
American Express 371449635398431
American Express Corporate 378734493671000
Australian BankCard 5610591081018250
Diners Club 30569309025904
Diners Club 38520000023237
Discover 6011111111111117
Discover 6011000990139424
JCB 3530111333300000
JCB 3566002020360505
MasterCard 5555555555554444
MasterCard 5105105105105100
Visa 4111111111111111
Visa 4012888888881881
Visa 4222222222222Note : Even though this number has a different character count than the other test numbers, it is the correct and functional number.
Processor-specific Cards
Dankort (PBS) 76009244561
Dankort (PBS) 5019717010103742
Switch/Solo (Paymentech) 6331101999990016

Original Source for these numbers is this.

I have just tried to sum up all the info that helped me with credit card numbers in one post. I hope this saves some time for other people.

  • zeeshan Tahammul

    great!

  • Pingback: How to test Credit Card numbers using Luhn’s... | PHP | Syngu()

  • Anonymous

    Testing this algorithm gives me an error on the: 
    76009244561  number.  I have tried on another online credit card checkers and it seems this number has an error based on the algo-luhn check.

    • Hey,

      As i said it works for “almost all” credit card numbers. I am sure the credit card number you have given here is mot generated using Luhn’s Algo hence this technique here can’t verify it. But all major credit card providers use the same standard hence they can be verified using this technique.

      • Anonymous

        Ok, I have only say you because that is the third example starting at the end on your examples list.

        I am porting your algorithm to C# here: http://www.ebys.es/en/85-technological/c/74-validating-credit-card-numbers-from-net.html

        Kind regards.

        • I understand.

          The credit card numbers are not there to test this algo though. they are just a list of credit card numbers that can be used for testing purposes of any sort.