You may have wondered what these numbers mean. Well, we can give you an idea. ANSI Standard X4.13-1983 answers this question for most credit cards—phone cards, gas cards and department store cards have their own system.
The first digit of the card identifies the type of card. A 3 is a T & E card. A 4 is a Visa. A 5 is a MasterCard. A 6 is Discover. American Express starts with a 37. Carte Blanche and Diners Club with a 38.
On your American Express cards the third and fourth digits are type and currency. The fifth through eleventh digits are the actual account number. Digits 12 though 12 are card number within account. And the fifteenth is a check digit.
On your Visa card, the second through the sixth digit are the bank number. The seventh through twelfth or fifteenth is the account number and the last digit is a check digit.
On you MasterCard, digits 2 and 3 are the bank number (this can also be digits 3, 4,5 and 6 depending on the bank). The digits following the bank number are the account number up through the fifteenth digit. And the last digit is a check digit.