Credit Card Number Verifier (MOD10)

Free software to verify credit card numbers

Credit Card Validation - Check Digits (MOD-10 Algorithm)

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.

Credit card validation can be used, for example, to validate credit card number keyed or said on the phone by a user before sending it our for debit authorization. If you are issuing your own cards, you may want to use MOD10 to encode their numbers validity.

1. Prefix, Length, and Check Digit Criteria

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
American Express 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

2. LUHN Formula (Mod 10) for Validation of Primary Account Number

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.

Make sure that you:

  1. have started with the rightmost digit (including the check digit) (figure odd and even based upon the rightmost digit being odd, regardless of the length of the Credit Card.) ALWAYS work right to left.
  2. the check digit counts as digit #1 (assuming that the rightmost digit is the check digit) and is not doubled
  3. double every second digit (starting with digit # 2 from the right)
  4. remember that when you double a number over 4, (6 for example) you don't add the result to your total, but rather the sum of the digits of the result (in the above example 6*2=12 so you would add 1+2 to your total (not 12).
 
 

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