The numbers on your credit card actually follow a universal standard which is used to identify specific functions. Each credit card has a different amount of numbers. Visa and Mastercard have 16, American Express has 15 and Diner’s Club has 14.
The first number on a credit card always identifies what type of credit card it is. Visa cards start with a 4, whereas Mastercard starts with a 5 and American Express with a 3. The remainder of the digits represent the account number, including the last number which is used to verify that your credit card is actually valid.
Credit cards also have additional verification numbers, which are mainly used when the card isn’t present for phone and online purchases. These are the three-digit numbers on the back of Visa and MasterCard or the four-digit numbers on the front of an American Express card.