Tuesday, January 29, 2019

Credit card numbering

The numbers found on credit cards have a certain amount of internal structure, and share a common numbering scheme.

The card number's prefix is the sequence of digits at the beginning of the number that determine the credit card network to which the number belongs. The card number's length is its number of digits.

The prefixes and lengths for the most common card types are:

  • Card Type Prefix(es) Length(s)
  • MasterCard 51-55 16
  • BankCard 560-561 16
  • Visa 4 13 or 16
  • American Express 34 or 37 15
  • Discover Card 6011 16
  • Diners Club / Carte Blanche 300-305, 36, or 38 14
  • JCB 35 15 or 16

In addition, the first 6 digits of the credit card number are known as the Bank Identification Number (BIN). These identify the institution that issued the card to the card holder.

Some credit card issuers choose to restrict the card numbers they issue to those which pass a checksum test, where the final digit of the card number is used to confirm the initial digits. This has two benefits of preventing casual attempts to invent credit numbers (only one in ten will be valid), and also prevent mistakes when the card number is manually recorded.

Collectible Credit Cards

A growing field of numismatics, or more specifically Exonumia, credit card collectors seek to collect various embodiments of credit from the now familiar plastic cards to older paper merchant cards, and even metal tokens that were accepted as merchant credit cards. Early credit cards were made of celluloid, then metal and fibre, then paper and are now mostly plastic.