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

The main number on your card is the Primary Account Number (PAN), and it is always 16 digits long for Visa, Mastercard, and Discover cards. American Express cards have 15 digits instead. These digits are not random — they follow a mathematical formula called the Luhn algorithm, which allows payment systems to spot typos or fraud before processing a transaction.

Beyond the 16-digit number, your card carries at least two more sets of numbers: the expiration date (month and year) and the CVV or CVC security code on the back. Some cards also display an issue number or a card sequence number, though these are less common in the United States. Each number serves a specific function in how your card works and how transactions are verified.

Key Takeaways

  • Your card's 16-digit Primary Account Number identifies your specific account and is the main number used to process purchases and payments.
  • The expiration date (printed as MM/YY) tells merchants and payment systems when your card stops being valid, usually four years after issue.
  • The three-digit CVV on the back (or four digits for American Express on the front) proves you physically possess the card during online or phone transactions.
  • The first digit of your PAN identifies the card network: 4 for Visa, 5 for Mastercard, 6 for Discover, and 3 for American Express.
  • Never share your full card number, expiration date, or CVV with anyone except a merchant you trust or your card issuer directly.

Breaking down the 16-digit Primary Account Number

The 16 digits on your card are divided into sections, each with a purpose. The first digit is the Major Industry Identifier (MII). A 4 means Visa, a 5 means Mastercard, and a 6 means Discover. American Express cards start with 3, which is why they have 15 digits instead of 16.

Digits 2 through 6 make up the Issuer Identification Number (IIN), also called the Bank Identification Number (BIN). This six-digit code tells the payment network which bank issued your card. When you swipe or insert your card, the terminal reads this code first to route the transaction to the correct processor.

Digits 7 through 15 are your account number — the unique identifier for your specific account at your bank. This is the number your bank uses internally to track your balance, payments, and transaction history. The final digit, number 16, is a check digit calculated using the Luhn formula. It exists only to catch errors; it does not identify anything about you or your account.

What the expiration date tells you

Your card's expiration date appears as two numbers: the month (01 through 12) and the year (the last two digits of the year). A card expiring 06/27 is valid through the end of June 2027. The expiration date is printed on the front of the card, usually in the bottom right corner.

This date marks when your card issuer stops honoring transactions on that physical card. It does not mean your account closes — your bank will typically mail you a replacement card with a new expiration date before the current one expires. If you do not receive a replacement, contact your bank. Online, you can often update your payment methods to use the new card number before the old one stops working.

Merchants and payment processors check the expiration date to ensure the card is still valid. If you try to use an expired card, the transaction will be declined. For recurring charges (subscriptions, automatic bill pay), you must update the expiration date with the merchant or the charge will fail.

The CVV and why it matters for online purchases

The CVV (Card Verification Value) or CVC (Card Verification Code) is a three-digit number printed on the back of your card, to the right of the signature strip. American Express prints a four-digit code on the front, above the card number. This code is not stored in the magnetic stripe or chip — it exists only on the physical card itself.

When you enter your card number online or over the phone, you must also enter the CVV. The merchant sends this code to the payment processor, which checks it against the code on file. If the codes match, it proves you have the physical card in your possession. A thief who steals your card number from a data breach cannot use it online without the CVV.

The CVV is never stored on a receipt, and legitimate merchants never ask you to provide it in an email or text message. If someone contacts you asking for your CVV, it is a scam. Your bank and the card network already have this information and do not need you to confirm it.

Less common numbers on your card

Some cards display an issue number or card sequence number, usually a single digit printed near the expiration date or on the back. This number increments each time your bank reissues your card — if your card is replaced due to damage or fraud, the new card might have an issue number of 02 instead of 01. Most merchants do not require this number, and it is becoming less common.

Older cards sometimes printed a hologram or security feature with an additional code, but these have largely been replaced by the chip technology embedded in modern cards. The chip itself does not display a number, but it stores encrypted versions of your card data and generates a unique code for each transaction, making it much harder to counterfeit than the old magnetic stripe.

How card numbers are used in transactions

When you make a purchase in person, the merchant's terminal reads your card number from either the chip or the magnetic stripe. The terminal sends the first six digits (the BIN) to the payment network to identify your bank. The network then routes the transaction to your bank for approval based on your available credit and account status.

Online, you type your full 16-digit number, expiration date, and CVV into a payment form. The merchant's payment processor encrypts this information and sends it to your bank. Your bank checks whether the transaction is within your credit limit and whether the CVV matches. If both checks pass, the transaction is approved and the merchant receives a confirmation code.

Over the phone, you read your card number to a customer service representative, who enters it into their system the same way an online merchant does. This is why it is important to call merchants directly using a number from your bill or their official website — never call a number provided in an unsolicited email or text, as it may connect you to a scammer.

Protecting your card numbers from fraud

Your 16-digit card number is the most sensitive piece of information on your card. If someone obtains it along with your expiration date and CVV, they can make online purchases or phone orders without your permission. Protect these numbers by never writing them down, never sharing them via email or text, and never entering them on a website unless you initiated the transaction and the site is secure (look for the padlock icon in your browser).

When you receive a new card, destroy the old one by cutting it in half or shredding it — do not throw it in the trash whole. If your card is lost or stolen, call your bank immediately using the number on your statement or the back of another card. Your bank can freeze the card within minutes, and you are not liable for fraudulent charges made after you report the loss.

For recurring payments (subscriptions, utilities, insurance), use your card's tokenized number if the merchant offers it. Tokenization replaces your real card number with a unique code that works only with that merchant, so a data breach at one company does not expose your number to others.

Frequently Asked Questions

Why does my American Express card have 15 digits instead of 16?

American Express uses a different card network standard than Visa, Mastercard, and Discover. The 15-digit format is part of their system design. The first digit is still 3 (identifying American Express), and the check digit still uses the Luhn formula, but the overall structure is different. Your 15-digit Amex number works the same way as a 16-digit Visa — it identifies your account and processes transactions normally.

Is it safe to give my card number to a merchant over the phone?

It is reasonably safe if you called the merchant using a phone number from your bill, their official website, or a directory listing. Never call a number from an email or text message, as it may be fraudulent. When you call, listen for the merchant's name in their greeting, and hang up and call back if anything feels wrong. Legitimate merchants have trained staff who handle card numbers securely every day.

What should I do if I see unfamiliar numbers or codes on my card?

Contact your card issuer immediately. Legitimate card numbers follow the patterns described here — 16 digits for Visa/Mastercard/Discover, 15 for American Express, a four-digit expiration date, and a three or four-digit CVV. If your card displays anything else or looks altered, it may be counterfeit or damaged. Your bank can issue a replacement.

Can someone use my card number if they only have the 16 digits?

Online, they would need the expiration date and CVV as well. In person, they would need the physical card to use the chip or magnetic stripe. However, if someone has all three pieces of information (number, expiration date, and CVV), they can make online purchases or phone orders. This is why you should never share your CVV with anyone except during a transaction you initiated.

Do I need to memorize my card number?

No. Most people do not memorize their card number, and there is no reason to. Keep your card in a safe place, and if you need the number for a transaction, retrieve it from the card itself or from your bank's app or website. Memorizing it increases the risk that you will accidentally share it or type it into an unsecured form.