A credit card has 15 or 16 digits, and each one does a specific job
The long number on the front of your credit card is not random. It breaks into four sections, and each section tells the card issuer, the merchant, and the payment network something different about the card and the transaction. Understanding what those numbers mean helps you spot fraud, know which card to use for which purchase, and understand what information you should never share online.
The total length is almost always 15 or 16 digits. American Express cards have 15. Visa, Mastercard, and Discover cards have 16. That difference matters because some older payment systems expect 16 digits and will reject a 15-digit card, though this is rare now.
Key Takeaways
- Credit cards have 15 or 16 digits total: the first digit identifies the card network, the first six digits form the bank identification number, digits 7 through 15 (or 16) are your unique account number, and the last digit is a check digit that catches typos.
- The card number itself is what you need to keep private; the expiration date, CVV, and cardholder name are additional security layers but should also be guarded.
- The first digit alone tells you the card type: 4 is Visa, 5 is Mastercard, 6 is Discover, and 3 is American Express.
- The last digit is calculated from the first 15 (or 14) using a mathematical formula called the Luhn algorithm, which helps payment systems catch accidental errors before they reach the bank.
The first digit: which payment network issued the card
The very first digit narrows down which company runs the payment network. A 4 means Visa. A 5 means Mastercard. A 6 means Discover. A 3 means American Express (though American Express cards start with 34 or 37, not just 3). This digit is set by the card network itself and never changes for that network.
This matters because different networks have different fraud protections, different merchant acceptance rates, and different rewards rules. When you are deciding which card to pull out at checkout, the first digit is already telling you which network you are using.
Digits 2 through 6: the bank identification number
The first six digits together form what is called the bank identification number, or BIN. This tells the merchant's payment system which bank issued the card and which specific product line it is. For example, one BIN might be a Chase Sapphire Preferred card, while another BIN from Chase is a Chase Freedom card.
When you swipe or insert your card, the merchant's terminal reads the BIN first. It uses that to route the transaction to the right bank, to check whether the card is active, and to confirm that the card type matches what the merchant expects. If you are using a business card at a retail store that only accepts consumer cards, the BIN can flag that mismatch before the transaction goes through.
You will see the BIN printed on your statement and in your card details online. You do not need to memorize it, but it is one reason why your card number is unique to you even though millions of people use the same bank.
Digits 7 through 15 (or 16): your account number
After the BIN comes your personal account number. This is the part that makes your card unique. Two people might both have Chase Sapphire cards (same BIN), but their account numbers are different. This section is usually 9 or 10 digits long, depending on whether your card is 15 or 16 digits total.
The account number is what the bank uses to find your specific account when a transaction comes in. It is also what ties the card to your credit report and your payment history. If you lose your card and the bank issues a replacement, the account number stays the same, but the full card number changes (because the last digit, the check digit, recalculates).
The last digit: the check digit that catches errors
The final digit is called the check digit. It is calculated from all the digits before it using a mathematical formula called the Luhn algorithm. The purpose is to catch typos before a transaction is processed.
Here is how it works in practice: when you type your card number into a website, the payment system runs the Luhn algorithm on the digits you entered. If the check digit does not match what the algorithm predicts, the system knows you made a mistake and rejects the entry before it ever reaches your bank. This saves time and reduces fraud attempts that rely on guessing card numbers.
You never need to calculate this yourself. The bank generates it when the card is made, and it stays the same for the life of that card. But it is why you cannot just change one digit of a valid card number and expect it to work — the check digit will not match.
The expiration date and CVV are separate from the card number
The 16-digit number is only part of the card's security. The expiration date (usually printed as MM/YY on the front) and the CVV (a three- or four-digit code on the back) are additional pieces of information that merchants use to verify you are the cardholder.
The expiration date tells the payment system when the card stops working. Most cards expire after three to five years. When your card expires, the bank issues a new one with a new card number and a new expiration date, even though your account stays the same.
The CVV (card verification value) is a security code that only you and the bank know. It is not encoded in the card number itself. Online merchants ask for it to confirm that you have the physical card in your hand. Never share your CVV with anyone, and never type it into a website unless you are completing a purchase.
What you should never share, and why
The card number, expiration date, and CVV together are enough for someone to make a purchase in your name. You should treat all three as sensitive information. Never type your full card number into an unsecured website (look for the padlock icon in the address bar). Never read your card number aloud in public. Never take a photo of the front of your card and store it in an unencrypted file or email it to yourself.
The cardholder name is printed on the card, but it is not secret — merchants see it every time you use the card. The card number, expiration date, and CVV are the three pieces that matter for security. If someone has all three, they can make online purchases without your permission.
Frequently Asked Questions
Why do American Express cards have 15 digits instead of 16?
American Express uses a different card numbering standard than Visa, Mastercard, and Discover. The 15-digit format has been their standard for decades. Some older payment systems were built to expect 16 digits and may reject a 15-digit card, but most modern systems handle both. If you run into a rejection, contact the merchant or your card issuer.
Can I figure out what bank issued a card just from the card number?
Yes, the first six digits (the BIN) tell you the bank and often the specific card product. You can look up a BIN using free online BIN lookup tools. This is useful if you find a lost card and want to contact the issuer, or if you are curious which bank issued a card you are considering.
What happens if I type my card number wrong?
If you mistype one digit, the check digit will not match, and the payment system will reject the entry before it reaches your bank. If you mistype the check digit itself but get everything else right, the system will also reject it. This is by design — it prevents accidental charges from typos.
Is the card number the same as my account number?
Not exactly. Your account number is part of the card number (digits 7 through 15 or 16), but the full card number also includes the BIN and the check digit. Your account stays the same when you get a new card, but the full card number changes because the check digit recalculates.
Do I need to memorize my card number?
No. Most people do not memorize their card numbers anymore. You can store it securely in your phone's wallet app, in a password manager, or straightforward pull the physical card out when you need it. The only time you might need it is for phone or mail orders, and you can look it up then.