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 16 digits long and runs across the front in four groups of four. This is your Primary Account Number (PAN), and it is the identifier that connects the card to your account. The first digit or first few digits identify which bank or card network issued it — Visa cards start with 4, Mastercard with 5, American Express with 3, and Discover with 6.
Beyond those 16 digits, your card carries two more sets of numbers: the expiration date (month and year, four digits total) printed below or near the main number, and the CVV or CVC code (three or four digits) on the back. American Express cards have a four-digit code on the front instead. These additional numbers serve different purposes in how your card is used and protected.
Key Takeaways
- The 16-digit number on the front is your Primary Account Number and uniquely identifies your card to the bank and payment networks.
- The expiration date (four digits) tells merchants and processors when your card stops being valid.
- The CVV or CVC code (three or four digits on the back) is a security feature that proves you physically have the card when you shop online or by phone.
- American Express uses a different card layout with the security code on the front, but the principle is the same.
- Never share your full card number, expiration date, or security code with anyone except a trusted merchant during a legitimate transaction.
What the 16-digit number actually does
Your 16-digit Primary Account Number is divided into sections that tell the payment system who you are. The first digit (the Major Industry Identifier) signals the card network — 4 for Visa, 5 for Mastercard, 3 for American Express, 6 for Discover. The next five or six digits (the Issuer Identification Number or IIN) identify your specific bank or credit union.
The remaining digits are your individual account number within that bank. When you swipe, insert, or enter your card number online, the payment processor reads this full number to route the transaction to your bank, confirm the card is active, and check that you have available credit. If even one digit is wrong, the transaction will be declined.
The expiration date and why it matters
Your card's expiration date appears as two digits for the month and two for the year (for example, 08/27 for August 2027). This date is printed on the front of the card, usually below the main number. The card stops working on the last day of that month, even if you have available credit.
Banks issue new cards before the old one expires, and you will receive the replacement card in the mail several weeks in advance. When it arrives, you can start using the new card when ready — you do not have to wait until the old one expires. Update any recurring payments (subscriptions, automatic bill pay) to the new card number and expiration date to avoid declined transactions.
The CVV or CVC security code and when you need it
The three-digit code on the back of your card (or four digits on the front of an American Express card) is called the CVV (Card Verification Value) or CVC (Card Verification Code), depending on the card network. This code proves you physically have the card in your possession. When you enter it during an online purchase or phone order, the merchant confirms that you are not just using a stolen card number.
The security code is never stored on the card's magnetic stripe or chip, so a thief who steals your card number alone cannot use it online without also knowing this code. You should never write this number down, save it in your phone, or share it with anyone except during an active, trusted transaction. Legitimate companies will never ask you to provide your CVV over email or phone unless you initiated the contact.
How American Express cards are different
American Express cards use a different layout. Instead of 16 digits, they have 15 digits on the front. The security code (called the CID) is a four-digit number printed on the front of the card, above the main number, rather than on the back. The expiration date still appears on the front in the same format as other cards.
When you use an American Express card online or by phone, you will still be asked for the card number, expiration date, and security code — the process is the same, just the location of the security code is different. Some older American Express cards may have slightly different formatting, but the principle remains: 15 digits for the account number, an expiration date, and a four-digit security code.
What happens if you lose track of these numbers
If you forget your card number, expiration date, or security code, you do not need to memorize them. Your bank can provide this information through your online account portal, mobile app, or by calling customer service. You can also look at a physical card if you have it.
If your card is lost or stolen, contact your bank when ready. They will cancel the card and issue a replacement with a new 16-digit number. You are not responsible for fraudulent charges made after you report the card missing, as long as you report it promptly. Your bank will send the new card by mail within 7 to 10 business days in most cases.
Why card networks use these specific number formats
The 16-digit format and the additional security codes exist because they solve real problems in payment processing. The 16 digits give enough combinations to issue billions of unique cards without repeating numbers. The expiration date forces cardholders to receive a new physical card periodically, which allows banks to update security features and catch fraud patterns. The CVV code adds a layer of protection for remote transactions where the card is not physically present.
These standards were set by the card networks (Visa, Mastercard, American Express, Discover) decades ago and have remained largely unchanged because they work. Newer cards now include a chip that encrypts the card data, and some cards support contactless payment, but the basic number structure has stayed the same for compatibility across millions of merchants worldwide.
Frequently Asked Questions
Is it safe to write down my credit card number?
No. Write down only the last four digits if you need to identify which card you are using. Keep the full number, expiration date, and security code only in your physical wallet or a password-protected app. If someone finds a written record of your full card number, they can attempt to use it online without needing the security code.
Can someone use my card if they only have the 16-digit number?
They can attempt online purchases, but most merchants now require the expiration date and CVV code as well. In-person transactions at a physical store require the physical card itself. If you notice unauthorized charges, report them to your bank when ready — you are not liable for fraudulent transactions once reported.
What if I give my card number to a merchant and they ask for more digits than usual?
Legitimate merchants ask for the 16-digit number, expiration date, and CVV code — nothing more. If someone asks for your PIN, your full Social Security number, or any other information, stop the transaction and contact your bank. Scammers sometimes pose as merchants or banks to collect additional information.
Do debit cards have the same number format as credit cards?
Yes. Debit cards issued by Visa or Mastercard have 16 digits, an expiration date, and a security code, just like credit cards. The main difference is that a debit card draws directly from your bank account rather than creating a bill you pay later. The card number format itself is identical.
Why does my new card have a different number than my old one?
Each physical card gets its own unique 16-digit number. When your bank issues a replacement card (whether because yours expired, was lost, or was compromised), the new card has a completely different number. You must update any recurring payments or saved cards with merchants to use the new number.