Why We'll Never Miss 16-Digit Credit and Debit Card Numbers

According to Cris Poor, professor of mathematics at Fordham University, the possible combinations of 16-digit credit cards generate many more account numbers than ever before. Poor says that 16-digit card numbers have 10 quadrillion possibilities.

In comparison, the world's population is only 6 billion.

"So, every person in the world could have more than a million potential credit numbers, and I do not know anyone who owns so many credit cards," Poor said.

To understand why we do not miss numbers, you need to know how the distribution of credit card numbers works.

All card number guidelines are defined by the International Standards Organization and the American National Standards Institute, which also sets standards for items such as the size and shape of credit cards. The first number represents the network and the industry. For example, all visas start with a "4", while AmEx cards begin with a "3". This allows merchants to identify who is ultimately responsible for paying fees.

The first digit, as well as the five that follow it, are collectively known as the Bank Identification Number (BIN). They are assigned to different payment networks (Visa, MasterCard, etc.), which then distribute them to card issuers (Bank of America, Wells Fargo, etc.).

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Thus, the six digits of each Chase Sapphire card, for example, would be the same as the first six digits of each Capital One Venture Rewards card. The next nine digits of your card are assigned to individual users by the issuers and are unique to your account.

This means that each issuer has millions of individual consumer account numbers that it can distribute.

"In general, a financial institution would not want to exhaust all the numbers in its range," said Lou Grilli, AVP Product Development at Trellance, a credit union services organization. "They want to keep it for re-issue and for growth or if they decide to add another card number to the family.

"Realistically, they would give about 50% of their number would be acceptable, and most BINs are used only about 10%," he added.

Even then, networks do not want to see their BIN capability tested. MasterCard BINs have always started with the number 5, but in 2017, the network started issuing two sets of cards to increase the number of cards and numbers available.