The Meaning Behind Credit Card Numbers

Credit card numbers can be anywhere from twelve to nineteen digits long. Most credit cards consist of sixteen numbers. What do they mean? Where do they come from?

The First Digit

All Visa credit cards start with a 4, all MasterCard a 5, all Discover a 6, and all American Express a 3. Why? It is called a Major Industry Identifier, or MII. Credit cards for gas stations such as Shell and Exxon typically start with a 7.

This is because the MII for banking and financial is a 4 or a 5, the MII 3 is categorized for travel and entertainment, a 6 is for merchandising and banking, and a 7 is for petroleum.

The Next Five

The next five digits in the credit card number are the bank number, or issue identifier. Some institutions will consider the first number as part of the identifier, but they remain set to their individual MII category.

Each institution that distributes credit cards will have its own unique identifier. This will vary by card type, however. Therefore, a bank issuing a MasterCard with a beginning number of 501234 will now issue a Visa with the number 401234.

Digit Seven through Second to Last

The next set of digits starts at the seventh one and continues to the second to last digit. This is your individual credit card account number.

The Last Digit

The last number in the credit card number sequence is called a check digit. This number is derived using the Luhn algorithm. This algorithm was patented in 1960 and named after the scientist Hans Peter Luhn who developed the technique.

Using the Luhn algorithm will only allow one possible correct digit to be used as the check digit.

Card Security Code

The Card Security Code, also called a Card Verification Code, is a three-digit number code that is on the back of the credit card. It is the number that ultimately validates use of the card. There is not set system, technique, or algorithm used to arrive at this number. Each issuing institution has its own way of coming up with a correct CVC number, and that system is known only by that institution.

The use for CVC numbers became apparent when individuals became familiar with the Luhn Algorithm. The knowledge of how the algorithm worked allowed individuals to come up with valid credit card numbers that were possibly real numbers already in use by cardholders.

With the Luhn Algorithm, there is a process to deciphering validity of a credit card. The end result is a number that is divisible by ten, although arriving at the end result is complex. Anyone could follow this process and come up with a valid credit card number to make purchases, especially on the Internet.

This is why the CVC was introduced. The three-digit code is derived somehow from the actual credit card number and the expiration date. Because there is not a set technique for arriving at the code, there is less fraudulent activity with credit card use.

Although it may be still be possible to come up with a valid credit card number using the Luhn Algorithm, it is impossible to decipher the number and come up with an expiration date and CVC. Attempting to do so could net you some federal fraud charges.

In addition to the expiration date and CVC, most retailers will require you to provide your billing zip code as well. These three pieces of information have all been set in place and are used to further prevent any type of credit card fraud.

If you like math and numbers, it is fun writing down 16 digits and using the Luhn algorithm to decipher if it could be a credit card number, but you should never try to use the number for any purchases.

(This article is meant for informational and entertainment purposes only. Mathematicians enjoy using the Luhn Algorithm for entertainment purposes, and that is the only reason individuals should use it. Credit card fraud is a crime.)