A credit card has 15 or 16 digits printed on the front, plus additional numbers on the back and sometimes the side — each one serves a specific purpose in processing payments and protecting your account.

The longest number on your card is the Primary Account Number (PAN), which is the 15 or 16 digits printed across the front. This is your unique card identifier — the number that appears on your statement and the one you enter when you shop online or over the phone. Visa and Discover cards typically have 16 digits. American Express cards have 15. Mastercard cards have 16.

The other numbers on your card are the expiration date (month and year), the CVV or CVC security code on the back, and sometimes a card verification value on the front. Together, these numbers let merchants and banks confirm that you own the card and that the card is valid.

Key Takeaways

  • The 15 or 16 digits on the front of your card is your Primary Account Number, which identifies your specific account to the card network and your bank.
  • The expiration date (printed as two digits for month and two for year) tells merchants and processors when your card stops being valid.
  • The CVV or CVC code on the back (three or four digits) is a security feature that proves you physically have the card when you shop online or by phone.
  • American Express prints a four-digit code on the front instead of the back, and some cards print a code on the front as well as the back.
  • The card number itself encodes information about your bank and card type in its first few digits, which is why different issuers' cards look different.

The Primary Account Number and What It Contains

The 15 or 16 digits on the front of your card are not random. The first digit or two identify the card network — Visa cards start with 4, Mastercard with 5, American Express with 3, and Discover with 6. The next several digits identify your specific bank or card issuer. The remaining digits are your unique account number within that bank's system.

This structure is called the Luhn algorithm, and it includes a check digit (usually the last digit) that lets computers verify the number is real before they even contact your bank. This is why a typo in your card number will often be rejected immediately — the check digit won't match.

When you use your card in a store, online, or over the phone, this full number is what gets sent to the payment processor. The processor uses the first digits to route the transaction to your bank, and your bank uses the full number to pull up your account and check your balance.

Expiration Date: Why It Matters and When It Changes

Your expiration date appears as four digits — two for the month and two for the year. A card that expires in March 2027 will show 03/27. This date is printed on the front of the card, usually below or to the right of the card number.

The expiration date tells merchants and payment processors that your card is still valid. After the last day of the month shown, the card stops working for new purchases. Your bank will typically mail you a replacement card 30 to 60 days before expiration, with a new expiration date printed on it.

If you have an old card that has expired, you can still use the number to look up past transactions on your statement, but you cannot use it to make new purchases. Some subscription services will ask you to update your card information if your card is expiring soon, even if you have not yet received the replacement.

The CVV or CVC Security Code on the Back

The three-digit number on the back of your card (or four digits for American Express) is called the CVV (Card Verification Value) or CVC (Card Verification Code), depending on the card network. This code is not encoded in the card's magnetic stripe or chip — it is printed on the card only, which means a merchant who has only your card number cannot use it without also having the physical card or a photo of it.

When you shop online or over the phone, you enter this code along with your card number and expiration date. The merchant sends all three pieces of information to the payment processor, which checks that the CVV matches the card number on file. If someone has stolen your card number but not the physical card, they cannot complete an online purchase without guessing the CVV.

American Express prints a four-digit code called the CID (Card Identification Number) on the front of the card, above the card number, instead of on the back. Some other card issuers print a code on both the front and the back for additional security.

Why Different Card Networks Have Different Digit Counts

American Express uses 15 digits while Visa, Mastercard, and Discover use 16. This difference comes from how each network designed its numbering system decades ago, and it has stuck around because changing it would require updating millions of merchant systems and payment processors.

The 15-digit format for American Express also means that some older online forms or payment systems that expect exactly 16 digits may reject an American Express card number, even though the card is valid. If you encounter this, contact the merchant — their system may need to be updated, or they may not accept American Express at all.

Visa and Mastercard both use 16 digits, but the numbers are structured differently. A Visa number tells you which bank issued it and which region it was issued in, while a Mastercard number has a different internal structure. These differences do not affect how you use the card, but they do help payment processors route transactions correctly.

Numbers You Should Never Share Online or Over the Phone

Your full card number, expiration date, and CVV are the three pieces of information a scammer needs to make an online purchase in your name. Never enter these numbers into a website unless you initiated the transaction and you are certain the website is legitimate (look for "https://" and a padlock icon in your browser).

Your bank and legitimate merchants will never ask you to provide your CVV in an email, text message, or phone call. If someone contacts you asking for these numbers, it is a scam. Hang up or delete the message.

Your card number alone is less dangerous than your card number plus CVV, but it is still sensitive information. If you see a charge on your statement that you do not recognize, contact your card issuer immediately. Most cards offer fraud protection that limits your liability for unauthorized charges.

What Happens When You Get a New Card

When your card expires or your bank issues you a replacement for any reason, you receive a new card with a new 15 or 16-digit number. Your old card number stops working, even though it is still associated with your account in your bank's records (so you can still look up old transactions).

If you have set up automatic payments or subscriptions using your old card number, you will need to update them with the new number. Your bank may send you a notice listing which merchants have your card on file, or you may need to log into each service and update it yourself. If you miss updating a subscription, the payment will fail and the service may suspend your account.

Some banks let you request a new card number without getting a physical replacement card — this is called a virtual card number or temporary card number. These numbers work the same way as a regular card number but are tied to your account and can be set to expire after a certain date or after a single use. They are useful for online shopping if you are concerned about fraud.

Frequently Asked Questions

Why does my card have numbers on the back besides the CVV?

Some cards print the last four digits of your card number on the back as well, for your reference. This helps you identify which card you are using if you have multiple cards from the same bank. The CVV is always a separate three or four-digit code printed on the back (or front for American Express).

Can someone use my card number if they do not have the CVV?

In a store, yes — they can use the card number with a magnetic stripe reader or chip reader without needing the CVV. Online or over the phone, no — the CVV is required. This is why in-person fraud is more common than online fraud, and why you should monitor your statement regularly for charges you do not recognize.

What if I accidentally gave someone my full card number and CVV?

Contact your card issuer immediately and ask them to cancel the card and issue a replacement. Your bank can monitor the account for fraudulent charges and will typically not hold you liable for unauthorized transactions made after you report the card compromised. The sooner you report it, the better.

Do I need to memorize my card number?

No. Keep your card in a safe place and use it when you need it. For online shopping, most browsers and payment services will save your card information securely so you do not have to type it in every time. Never write your card number down or store it in an unencrypted file.

Why do some websites ask for my billing zip code instead of my CVV?

The billing zip code is an alternative security check called AVS (Address Verification System). It is less secure than the CVV because your zip code is easier to find, but some merchants use it instead of or in addition to the CVV. Both methods are designed to confirm you have the card.