What Is a Credit Card Number?

Your credit card number is a set of digits that can be seen on the front or back of your credit card. Often, the digits can appear in sets of four. Your credit card number may appear random, but it is anything but! Your credit card’s digits are coded to identify your credit card’s network, the card issuer, and the unique card itself. When you use your card, the card’s information is processed by a payment processor that verifies the account with the card issuer, facilitating a transaction.

Your credit card’s digits each have a specific purpose. Here's a look at how each of these digits break down:

The First Credit Card Digit

If you look at the credit card in your wallet, it may start with a 3, 4, 5, or 6. This first number is called the major industry identifier (MII) number, and it shows the primary industry associated with the card or card issuer. The 3 through 6 range represents MIIs most used by the majority of personal credit card issuers. Some other MII examples include 1, designating an air travel and financial services issuer, and 7, which is primarily used for cards issued in the petroleum industry.¹

The Second Through Sixth Digits

The next five-digit set of numbers is called the issuer identification number (IIN) or the bank identification number (BIN). These numbers refer to the credit card company that issued the card, and also identified which payment network the card belongs to.²

The Seventh Through 14th or 15th Digits

This section immediately follows the IIN. The individual account number is assigned by the card issuer and is unique to each credit card account. However, keep in mind that your account number and card number aren’t the same.³

While the MII and IIN let merchants know what institution the money is coming from, this section can tell them which accounts may be charged.

The Last Digit

The individual account number is immediately followed by the “check digit.” If you’ve ever wondered why a minor typo doesn’t accidentally charge someone else’s card when making an online purchase, it’s because of this check digit. This last number serves as a quick check to determine whether a credit card number is legitimate.⁴

Most credit cards may use a public domain formula, called the Luhn algorithm, to verify accounts. It’s a fairly simple calculation that, put simply, involves adding up each digit of the card number in a particular manner. If the sum ends in a zero, the card passes the algorithm and is a potential credit card number.

It’s important to note that the Luhn algorithm isn’t designed to protect anyone from fraud or theft. Instead, it gives most merchants, especially automated ones like online retailers, a quick way to protect against accidental errors, such as accidentally typing a 5 instead of a 6 or entering an extra number.