The Secret of Credit Card Numbers - Page 3

The remaining numbers in the series are used for different purposes depending upon the card type and issuer.

In most cases, the next group after the opening series of numbers represents the routing number of the card-issuing bank, the group after that is the user's account number, and the final digit is a check digit. The check digit is a number that is calculated by applying a special formula to all of the other numbers. The check digit is the result of that formula and is used as an anti-fraud check.

To keep things from getting too confusing, look at your card as you follow along for the next steps.

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