How Credit Card Numbers Work
What the digits mean
Most card numbers are 15 to 16 digits with structure. The first digit signals the network (4 for Visa, 5 for Mastercard, 3 for American Express, 6 for Discover). The first six to eight digits are the bank identification number (BIN), which identifies the issuer. The middle digits are your individual account number, and the final digit is a check digit (a Luhn formula) that catches typos.
The other security pieces
The long number alone is not enough to charge your card; payments also need the expiration date and the CVV security code, which is not stored in the number. That layered design is a basic fraud defense. In mobile wallets, your real number is replaced by a device-specific token, so the merchant never sees it.
Protect it
Treat the full number, expiry, and CVV together as you would a password: enter them only on trusted checkouts, never share them in response to an unsolicited message, and use virtual card numbers online where possible. If the number is compromised, your fraud protection covers unauthorized charges and the issuer reissues a new number.
Frequently asked questions
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