Credit Card Number

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The numbers on every credit card are much more than a string of randomised numbers issued for each individual customer. They in fact adhere to international standards describing both the location and history of the credit card. In this article, learn about what the credit card number sequences on each credit card means, how they assist in credit card fraud, and what the other features signify.

Credit card number in a nutshell

  • Most credit cards have 15 or 16 digits displayed across the front, depending on the issuer
  • The first 6 digits indicate the issuer number, the next five refer to the specific issuing bank, and the final six equal the user’s account number
  • Credit cards are secured from transcription errors via the Luhn algorithm, an equation which makes sure the remaining numbers equal the check digits
  • Credit cards also include an expiration date and CVV, which provides further assurance that the card belongs to its holder

What do the credit card numbers on each card mean?

The majority of credit card issuers (Visa and Mastercard) have 16 digits displayed across their cards. American Express has 15. 

The first six digits of the number indicate the Issuer Identification number or IIN. The first digit is the Major Industry Identifier or MII.

  • 5 = Mastercard
  • 4 = Visa
  • 3 = American Express

The following five digits refer to the specific issuing bank. It is with these numbers that the necessary exchange of information for every transaction can take place. 

Mastercard: 2 and 3; 2 to 4; 5; or 6

Visa: 2 to 6

American Express: 3 and 4 (indicating whether the card is Platinum, Delta, etc.)

The next six numbers indicate the account number. Usually six in total, the number of digits can also reach up to twelve. This sequence of numbers is assigned to individual customers.

Below see a shorthand visual representation of the above information:

Card issuerFirst 6 digitsNext 5 digitsLast 6 digits
Mastercard5-2, 3, 2 – 4, 5, 6Customer account number
Visa4-2 – 6Customer account number
American Express3-3, 4Customer account number

Card security and the Luhn algorithm

The other important feature of the credit card is embedded within the numbers itself. Invented by scientist Hans Peter Luhn, it is a simple algorithm which is used to validate identification numbers. IMEI numbers, South African Identification numbers, and credit card numbers can all be deemed valid via the algorithm. 

Instead of malicious attacks—against which card companies employ more complex security methods—the Luhn algorithm is a check for accidental errors. Institutions use it to distinguish legitimate credit card numbers from mistyped ones. For instance, when users type their credit card digits into any online shopping website, the website will automatically determine if the number is invalid when a mistake is made. 

Other credit card components

In addition to the number on the front of credit cards, the back of the card includes an expiry date (MM.YYYY format) and the CVV number. 

The Card Verification Value is a three or four-digit number which functions as another mode of verification and protection. When a card machine registers the CVV, further assurance is provided that the current user is the owner of the card and that it hasn’t been stolen.

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