What is a Credit Card Number?

The first six to eight numbers

The first four to eight digits of a credit card number make up the issuer identification number (IIN). Some financial institutions may also call it a bank identification number (BIN). This number identifies the financial institution that issued the card.

The IIN contains two pieces of information:

The first number

The first digit of a credit card number is the major industry identifier (MII). This digit identifies a credit card issuer’s industry. It may also identify the credit card network that your card is on. Here’s each MII and the industry it represents:

The next five to seven numbers

Taken with the MII, the next five to seven numbers indicate the card issuer. Different card networks may use IINs of different lengths, though new issuers are generally standardized at IINs of eight digits (including the MII). Older cards that use shorter IINs still work, though.

The rest of the numbers (minus the last one)

All remaining digits in a card number, except the final digit, represent the individual credit card account number. If you get a new credit card, these numbers may be different than the ones on your last card. If you get a virtual credit card number, it may be different from the number on your actual credit card, too.

The last number

The last digit of a credit card number is called the checksum. When you use your card, an algorithm uses this number to confirm that the credit card number has been entered correctly. The checksum, also known as the “check number” or “check digit”, is based on a formula known as the Luhn algorithm.

The Luhn algorithm can help detect errors when people enter a card number incorrectly.

Credit card numbers vs. account numbers

While credit card numbers and account numbers are related, they’re not always the same. Your credit card number refers to a specific card. Your account number is tied to your account with the card issuer. This might be your financial institution.

At some credit card companies, cardmembers with multiple credit cards might have several credit card numbers. However, the company might give you a single account number. You can find your account number on your credit card statement.

At Discover^®, your credit card number and account number are the same. To safeguard your account information from fraud and theft, your credit card number will only appear on the physical card. Any communication from Discover will only list the last four digits of the account number (this includes your monthly credit card statement).

Where is the security code on a credit card?

Your credit card number isn’t the only important number on your physical credit card. The card verification value (CVV) is a three- or four-digit number that acts as a security code. To make an online purchase with the card, or a purchase over the phone, you’ll need to enter the CVV.

This makes fraudulent transactions more difficult. While credit card issuers may differ, you can often find your credit card’s security code on the back of the card near the signature box.

The bottom line

Credit card companies don’t assign credit card numbers randomly. Every credit card comes with a unique set of numbers that serves a purpose.

There are four parts to a credit card number:

1. Major industry identifier (MII)
2. Issuer identification number (IIN) or bank identification number (BIN)
3. Account number
4. Checksum

Cards also include a card verification code used to prevent identity theft and credit card fraud.