Anatomy of a credit card account number

Those numbers on the front of your credit card? They aren’t just random. They give away specific information about your card and where it comes from.

The first digit of your credit card number is the industry identifier. This tells you the industry of the credit card issuer.

For example, airline industry cards begin with a one or a two. Travel or entertainment cards, such as American Express and Diners Club cards, begin with a three. All Visa credit cards start with a four, MasterCard with a five, and six is dedicated to Discover.

The first six digits of your card, including the industry identifier, represent the issuer identification number. This identifies the bank that issued the card.

And then, of course, there’s your personal account number. This is made up of the seventh digit on — everything except the last number on your card.

The final digit on your credit card is known as the check digit or checksum. This number is set by something called the Luhn formula, patented by an IBM scientist in 1960. It’s a formula that uses the numerals in your card’s account number to verify that it’s valid.

Various combinations of the card’s digits must ultimately add up to a number divisible by 10. The formula is mostly used to protect against input errors.

For example, let’s say you enter in the wrong numbers on an online shopping site. The formula will compute that the digits don’t add up right — telling you you’ve entered an invalid card number. That last digit of your credit card makes sure the formula works like it’s supposed to.

And now you know — there’s a lot of information on that little card in your wallet. Kristin Wong, CreditCards.com.