The First Digit

Gasoline cards, department store cards and phone cards have their own programs.

The major credit card companies operate on a standardized system for assigning credit card numbers. The first digit in the series will always be a 3, 4, 5 or 6. This number designates the type of card you have. For instance, a 3 means it`s a travel and entertainment card, such as American Express or Diners Club. A 4 is Visa and Visa-branded debit cards, cash cards; a 5 is MasterCard and MasterCard-branded debit cards, cash cards; and 6 is Discover.

The Other Numbers

American Express and Diners Club use the second digit to identify the company. That means that Diners Club cards will start with either 36 or 38, and American Express cards will lead off with 34 or 37.

The remaining numbers in the series are used for other purposes, depending upon the card type and issuer. Generally, the numbers grouped after the opening series is the routing number of the bank and the next group is the user`s account number. The final digit is special -- a check digit. This is a number calculated by applying a specific formula, and it is used as a fraud check.

Look At Your Card

American Express uses digits 3 and 4 for business or personal card type and the currency of the cardholder`s country of origin. Digits 5 through 11 are the account number. Digits 12 through 14 show the card number attached to that account. The last digit is, of course, the check digit.

Visa uses digits 2 through 6 for the bank number. Beginning with digit 7 and running through 12 or 15, they`re the account number, and the last number is the check digit. The number of digits in a group may vary because Visa cards don`t all have the same number of digits.

With MasterCard, the second digit through digit 3 (to as high as 6) is the bank number. All remaining digits, except the end check digit, identifies the cardholder`s account.

And that`s it. A slightly complex system necessary to track billions of credit cards across the globe.