What Does Your Credit Card Number Mean?

Most of us are curious beings by nature. So, if you’ve been staying awake at night wondering what your 16-digit credit card number means, it’s your lucky day.

I’m going to pull back the curtain and show you not only what the numbers represent, but also how they’re designed to catch an invalid credit card account number. I know the suspense is killing you, so let’s get to it.

Decoding Your Credit Card Number

There are standards for the account numbers, and this falls under the purview of the International Organization for Standardization. The ISO is an independent, nongovernmental international organization.

So, credit cards, which generally have between 13 and 16 account numbers, aren’t just random. Each digit conveys identifying information about the credit card, and the assigned numbers must follow the guidelines set by the ISO.

However, there is some variation in the way the standards are applied, and you’ll see what I mean when we get to the second set of numbers.

The first number.

Numbers 2 to 6.

Numbers 7 to 15 (or more).

The last digit.

[READ: Best Credit Cards for Young Adults.]

The First Number

This number is called the MII, or major industry identifier, and it specifies the card network and industry. If your card starts with 3, your card uses the American Express network. Visa starts with 4, a Mastercard is 5 and Discover is 6.

Other numbers are used to identify the industry. For instance, 1 and 2 are used for the airline industry. The numeral 3 represents travel and entertainment, so it makes sense that 3 also indicates it’s an American Express card. (AmEx cards largely focus on travel.)

Here’s a full list of MII digits:

1. Airlines.

2. Airline and other industry assignments.

3. Travel and entertainment.

4. Banking and financial.

5. Banking and financial.

6. Merchandising and banking.

7. Petroleum.

8. Telecommunications and other industry assignments.

9. Open for assignment.

Numbers 2 to 6

This group of numbers is called the issuer identification number. Generally, these numbers help identify the credit card company or institution that issued the credit card.

But note that different credit cards might have slightly different numbering systems. For instance, Visa uses the second through sixth numbers for the bank number. But American Express uses the third and fourth digits to identify the type of card and currency used.

[Read: Best Starter Credit Cards.]

Numbers 7 Through 15 (or More, Depending on the Length of the Account Number)

These numbers are related to the cardholder’s account. The numbers in this group are unique to an issuer, and they help with routing the information to the proper channels.

The Last Digit

The caboose of the account number has an important role. It’s called the check digit, and it’s designed to make sure all the account numbers represent a valid credit card number.

Payment processors use a checksum formula called the Luhn algorithm. It was invented by Hans Peter Luhn of IBM. It’s used to determine if the credit card numbers have a logical pattern. If the numbers don’t work with the algorithm, it isn’t a valid credit card number.

Where Is the Security Code on a Credit Card?

This is a three- or four-digit number, and it’s often called the CVV, or card verification value. The location of the CVV depends on the network payment processor that’s used.

Visa, Mastercard and Discover: These networks have a three-digit CVV, and it’s located on the back of the card.

American Express: This network has a four-digit CVV, and you can find it on the front of the card.

The CVV is designed to increase security, since you’d most likely need to have the card in your hand to know this code number. For instance, if someone stole your credit card number and tried to purchase something online, unless the thief knows your CVV, that person won’t be able to complete the purchase.

This code also comes into play when you order a pizza by phone. You give the credit card number, and the restaurant employee asks for the expiration date and the CVV. This is easy to answer, of course, if you’re looking at the actual credit card.

[Read: Best Cash Back Credit Cards.]

This isn’t foolproof by any means. It’s possible a thief could have your physical card and have access to the CVV. But the security code does provide another layer of security against some kinds of fraud. In particular, it combats what’s called ” card-not-present fraud,” or CNP fraud, which can occur online and on the phone.

So, be sure you guard your CVV number. And when you do share it, make sure you’re on a secure website or on a phone call that you initiated.