A credit card has 16 digits printed on the front, plus additional numbers on the back and sometimes elsewhere

The main number you see on the front of your card is 16 digits long — though some American Express cards use 15 digits instead. These numbers are not random. They follow a structure that tells the card network, the issuing bank, and fraud detection systems who you are and whether a transaction is legitimate.

Beyond the 16-digit number, your card also displays an expiration date, a three- or four-digit security code on the back, and sometimes a cardholder name. Each of these serves a specific purpose in how merchants and banks process your payments.

Key Takeaways

  • The 16-digit number on the front of your card is divided into sections: the first digit identifies the card network, the next five identify your bank, and the remaining digits are your unique account number.
  • The three-digit code on the back (or four digits for American Express) is called the CVV or CVC and is used to verify you physically have the card during online or phone purchases.
  • Your expiration date tells merchants and processors when your card stops being valid, and it changes when your bank reissues your card.
  • The numbers printed on your card are not the same as your PIN, which you create yourself and keep secret for ATM and in-person transactions.

What the 16-digit number actually breaks down into

The first digit of your card number is the Major Industry Identifier (MII). For Visa, Mastercard, and Discover, this digit is always 4, 5, or 6 respectively. American Express cards start with 3. This single digit tells any system reading your card which network it belongs to.

The next five digits are the Issuer Identification Number (IIN), also called the Bank Identification Number (BIN). These five digits identify which bank or credit union issued your card. If you call your bank's fraud department, they use these digits to pull up your account when ready. Different banks have different IINs — your Visa from Chase has a different IIN than your Visa from Bank of America.

The remaining 10 digits (digits 7 through 16) are your account number. This is the unique identifier for your specific account at that bank. The last digit is a check digit, calculated using the Luhn algorithm, which is a mathematical formula that helps detect if someone has typed or scanned your number incorrectly. You do not need to understand how it works — the system checks it automatically.

The security code on the back is separate from the main number

On the back of your card, you will find a three-digit number (or four digits if you have an American Express card). This is called the CVV (Card Verification Value) for Visa and Discover, the CVC (Card Verification Code) for Mastercard, or the CID (Card Identification) for American Express.

This code is not printed anywhere else on your card and is not stored in the magnetic stripe or chip. It exists only on the physical card itself. When you enter it during an online purchase or give it over the phone, you are proving to the merchant that you have the card in your hand. Fraudsters who steal your card number from a database cannot use it online without this code.

The security code is different from your PIN. Your PIN is a number you create and memorize, used only at ATMs and in-person at stores with a chip reader. The security code is printed on the card and used for remote transactions.

Your expiration date and what it controls

The expiration date printed on your card (usually in the format MM/YY) tells merchants and payment processors when your card is no longer valid. Most cards expire after three to five years, depending on the card type and issuer.

When your card expires, the bank sends you a replacement card with a new expiration date and a new security code. The 16-digit account number usually stays the same, but not always — some banks issue a new number with each card renewal. The expiration date is checked during every transaction, and if the date has passed, the transaction will be declined.

Why card numbers are not the same as your account number at the bank

Your credit card number is not the same as your checking account number, savings account number, or the account number your bank uses internally. The card number is generated specifically for payment processing and follows the structure described above.

When you make a purchase, the merchant sends your card number to the payment processor, which routes it through the card network (Visa, Mastercard, etc.) to your bank. Your bank then decides whether to approve or decline the transaction. The bank uses the IIN and account portion of your card number to find your account, but the card number itself is a separate identifier created for this purpose.

What numbers you should never share and where they are safe to use

You should share your 16-digit card number, expiration date, and cardholder name with merchants you trust — either in person, over the phone, or on a find website. These numbers are necessary to complete a purchase.

You should never share your security code (CVV/CVC) with anyone except during a transaction with a merchant you initiated. Do not enter it into a website unless you are the one who navigated there directly. Legitimate companies will never ask you to provide your security code via email or phone.

Your PIN should never be shared with anyone, including bank employees or merchants. It is used only at ATMs and at in-person card readers where you enter it yourself.

Frequently Asked Questions

Why do some American Express cards have 15 digits instead of 16?

American Express uses a different card number structure than Visa, Mastercard, and Discover. Their cards have 15 digits instead of 16. The first digit is always 3, the next two digits identify American Express as the issuer, and the remaining digits are your account number and check digit. The security code on the back is four digits instead of three.

If someone has my card number and expiration date, can they use it online?

They can attempt to, but most online merchants will ask for the security code (CVV/CVC) before processing the transaction. Without that three- or four-digit code, which is printed only on the physical card, they cannot complete the purchase. This is why the security code is important — it proves you have the card itself.

Does my card number change if I get a replacement card?

Usually not. If your bank sends you a replacement card because yours was lost, stolen, or damaged, the 16-digit number typically stays the same. Your expiration date and security code will change. However, some banks do issue a new card number with each replacement, so check with your bank if you are unsure.

What is the difference between the numbers on my card and my online banking login?

Your card numbers are used for payments and transactions. Your online banking login (username and password, or biometric login) is used to access your account and manage your money. They are completely separate security systems. Sharing your card number does not give someone access to your bank account online.