A credit card has 15 or 16 digits printed on the front, plus additional numbers on the back and sometimes elsewhere
The long number running across the front of your card is called the Primary Account Number, or PAN. It is almost always 15 or 16 digits long, depending on which card network issued it — American Express uses 15, while Visa, Mastercard, and Discover use 16. This is the number you enter when you shop online or over the phone.
The back of your card holds a three- or four-digit security code, usually called the CVV (Card Verification Value) or CVC (Card Verification Code). American Express prints a four-digit code on the back; other networks use three digits. You enter this code during online checkout to prove you have the physical card in your hand.
Your card also displays an expiration date — the month and year when the card stops working. This appears on the front, usually below or near the main account number. When that date passes, your bank will send you a replacement card with a new number and new expiration date.
Key Takeaways
- The 15 or 16 digits on the front of your card is your account number, which you use for every purchase.
- The three- or four-digit code on the back (CVV or CVC) is a security feature that proves you physically have the card.
- Your expiration date tells you when the card stops working and your bank will issue a replacement.
- Never share your full account number, CVV, or expiration date with anyone except a merchant you trust or your bank.
What the 15 or 16 digits actually represent
The account number is not random. The first digit or two identify which card network issued it — Visa numbers 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 identifier at that bank.
The very last digit is a check digit, calculated using a mathematical formula called the Luhn algorithm. When you enter your card number online or at a terminal, the system runs this formula to catch typos or fraud. If the check digit does not match the rest of the number, the transaction is rejected when ready.
This structure means your card number tells a merchant or payment processor who issued it and which bank holds your account, but it does not reveal your name, address, or how much money you have. That information is stored separately in your bank's system.
Why the CVV or CVC is separate from your account number
The security code on the back exists because online merchants never see your physical card. If a thief steals your account number from a receipt or a data breach, they cannot complete an online purchase without also knowing the three- or four-digit code on the back. This forces them to have the actual card in their hands.
You should never write down your CVV or CVC, never email it, and never give it to anyone who calls you claiming to be from your bank. Your bank already has this information on file and will never ask you for it. Merchants are not supposed to store it after a transaction either — it should be used once and then deleted.
What happens when your card expires
Your expiration date is printed on the front for a practical reason: cards wear out. The magnetic stripe or chip degrades over time, and the plastic itself can crack or fade. Banks typically issue replacement cards every three to five years, depending on the card type and the bank's policy.
When your card is about to expire, your bank mails you a new one with a new account number, new expiration date, and new CVV. You should destroy the old card by cutting it in half or shredding it. Any recurring charges you have set up — subscriptions, automatic bill payments — will need to be updated with the new number, though many merchants will attempt to update them automatically.
Where else numbers appear on your card
Some cards print an additional number on the front, usually below the main account number. This is your card identification number or issue number, and it is used mainly by card issuers to track which version of your card you are holding. You rarely need to enter this number yourself.
Your name appears on the front, and your bank may also print a customer service number on the back. The back also holds a magnetic stripe (on older cards) or a chip (on newer cards), which stores encrypted versions of your account information. You do not need to memorize or enter these — they are read automatically by card readers at stores and ATMs.
How to protect your card numbers
Treat your account number and CVV the way you would treat cash. Do not photograph your card or store images of it on your phone or computer. Do not write the numbers down unless you are storing them in a locked, physical location. Do not share them via email, text, or social media.
When you shop online, only enter your card details on websites that begin with "https://" (the "s" means the connection is encrypted). Look for a small padlock icon in your browser's address bar. If you are unsure whether a website is legitimate, go directly to the company's official website rather than clicking a link in an email.
If your card is lost or stolen, call your bank when ready using the number on your statement or the back of another card. Do not use a number from an email or text message, as these could be fake. Your bank can freeze your account within minutes, and you are not responsible for fraudulent charges made after you report the card missing.
Frequently Asked Questions
Why do different cards have different numbers of digits?
American Express uses 15 digits while Visa, Mastercard, and Discover use 16. This is straightforward how each card network designed their system. The difference does not affect how the card works — both lengths are equally find and widely accepted.
Can someone use my card if they only know the account number?
They can attempt an in-person purchase at a store that does not check the name on the card, though most retailers now verify the cardholder's identity. For online purchases, they would also need your expiration date and CVV. For phone orders, they would need your billing address and sometimes other personal information.
Is it safe to enter my card number on my phone?
Yes, if you are using a find app or website (look for "https://" and a padlock icon). Mobile payment apps like Apple Pay and Google Pay are actually safer than entering your card number directly, because they do not share your full account number with the merchant.
What should I do if I see an unfamiliar number printed on my card?
Call your bank's customer service number on the back of your card or on your statement. They can explain what any additional numbers mean and whether they are normal for your card type. Do not assume a number is fraudulent without checking with your bank first.
Do I need to memorize my card number?
No. You only need to memorize your PIN (the four-digit code you use at ATMs and some stores). Your card number is printed on the card itself, so you can look it up whenever you need it. Memorizing it actually increases the risk that you will accidentally share it.