The Language of Numbers on Your Credit Card

Ever wonder what the numbers on your credit card mean? Surprisingly, each number has a significant representation patterned in a systematic and standardized way to keep accounts organized and cardholders identifiable. It’s an intricate system with a sophisticated design to handle a masses of cardholders.

The major industry Identifier (MII) is the first number on your credit card. This number represents the entity’s category that issued your credit card. The numbers that symbolize the category of entity are from 0-9. For example under number “3” can be American Express or Diner’s club, or number “4 or 5” can be Discover Card or MasterCard.

The issuer identifier can be seen in the first 6 digits including the MII. The possible number of issuers is one million. After the first indicated number, the next three digits are defined by the three-digit country code as part of the issuer identifier. The remaining two digits are defined by the national standards body of the specific country.

The individual account identifier represents the possible account numbers the issuer has and it can be found from the seventh digit to the second to last one. The credit card's quota of numbers is 19. Since the individual account identifier starts from 7, simply subtract 7 from 19 and you get 12 digits, and 12 digits represent a trillion. This means that the issuer can have a maximum of a trillion account numbers or less.

The last number is called the check digit, which is properly obtained through the use of the Luhn algorithm, after Hans Peter Luhn. For the card that has an even number of digits, simply double every odd digit number and minus 9 if the product is greater than 9. Then, add all even digits along with the doubled-odd digits. The result must be a multiple of 10, otherwise it is not a valid card. If it turns out odd, try doubling the even numbers instead.

The system is quite complex; however, it took a practical mind to think of how to organize, identify, and verify accounts. Next time you pull out your credit card, take the time to appreciate the system and understand it.