This document outlines procedures and algorithms for Verifying the accuracy and validity of credit card numbers. Most credit card numbers are encoded with a "Check Digit". A check digit is a digit added to a number (either at the end or the beginning) that validates the authenticity of the number. A simple algorithm is applied to the other digits of the number which yields the check digit. By running the algorithm, and comparing the check digit you get from the algorithm with the check digit encoded with the credit card number, you can verify that you have correctly read all of the digits and that they make a valid combination.
Possible uses for this information:
Here is a table outlining the major credit cards that you might want to validate.
CARD TYPE | Prefix | Length | Check digit algorithm |
MASTERCARD | 51-55 | 16 | mod 10 |
VISA | 4 | 13, 16 | mod 10 |
AMEX | 34
37 | 15 | mod 10 |
Diners Club/ Carte Blanche | 300-305 36 38 | 14 | mod 10 |
Discover | 6011 | 16 | mod 10 |
enRoute | 2014 2149 |
15 | any |
JCB | 3 | 16 | mod 10 |
JCB | 2131 1800 | 15 | mod 10 |
The following steps are required to validate the primary account
number:
Step 1: Double the value of alternate digits of the primary account number beginning with the second digit from the right (the first right--hand digit is the check digit.)
Step 2: Add the individual digits comprising the products obtained in Step 1 to each of the unaffected digits in the original number.
Step 3: The total obtained in Step 2 must be a number ending in zero (30, 40, 50, etc.) for the account number to be validated.
For example, to validate the primary account number 49927398716:
Step 1:
4 9 9 2 7 3 9 8 7 1 6 x2 x2 x2 x2 x2 ------------------------------ 18 4 6 16 2
Step 2: 4 +(1+8)+ 9 + (4) + 7 + (6) + 9 +(1+6) + 7 + (2) + 6
Step 3: Sum = 70 : Card number is validated
Note: Card is valid because the 70/10 yields no remainder.
Because I get at least a letter a week regarding this routine, here are some additional helpful notes:
Make sure that you: