A credit card has 16 digits printed on the front, plus three or four more on the back — and each set of numbers does something different.

The 16-digit number on the front is your primary account number, or PAN. This is the main identifier that connects the card to your account. When you swipe, insert, or tap your card at a store, this is the number being read. It's also the number you give when you order something online or over the phone.

The three or four digits on the back — usually on the signature strip — are called the Card Verification Value (CVV) or Card Security Code. American Express cards have a four-digit code on the front; Visa, Mastercard, and Discover cards have a three-digit code on the back. This number is a security feature. It proves you physically have the card in your hand, which is why online retailers ask for it but the store cashier never does.

Your card also has an expiration date printed on the front, usually in the format MM/YY (month and year). This tells you when the card stops working — the last day of that month. When your card expires, the issuer sends you a replacement with a new expiration date, though your account number usually stays the same.

Key Takeaways

  • The 16-digit number on the front is your account number and is used for every transaction, whether in person or online.
  • The three or four digits on the back (CVV or security code) are only needed for online and phone purchases, not in-person transactions.
  • Your expiration date tells you the last month your card will work; you'll receive a replacement before it expires.
  • Never share your CVV with anyone unless you're making a purchase, and never write it down or store it in your phone.

How the 16-digit number is organized

The 16 digits aren't random. The first digit tells you the card network: Visa cards start with 4, Mastercard with 5, American Express with 3, and Discover with 6. The next five or six digits identify your bank — the issuer. The remaining digits are your unique account number within that bank's system.

This structure matters because it's how the payment system routes your transaction. When you use your card, the network (Visa, Mastercard, etc.) reads those first digits, finds your bank, and your bank confirms you have the funds or available credit. The whole process takes seconds.

Why you need the CVV but shouldn't store it

The CVV exists because online fraud is easy if someone only has your 16-digit number. A thief with your account number and expiration date can make online purchases. But they can't complete most online transactions without the CVV — it's printed on the card itself and isn't stored in the payment system's database. This means even if a retailer's database gets hacked, the CVV isn't there to steal.

This is why you should never write your CVV down, photograph it, or store it in your phone or email. If someone gets your full card number, expiration date, and CVV, they have everything needed to make purchases. Your account number and expiration date are less sensitive — you have to give them out to make purchases — but the CVV should stay private.

What happens when your card expires

Your card expires on the last day of the month shown on the front. After that date, the physical card won't work at any store or ATM. However, your account doesn't close. Your bank will mail you a replacement card with a new expiration date, usually arriving two to three weeks before your current card expires.

If you have recurring charges set up — a subscription, a gym membership, an automatic bill payment — you'll need to update those with your new card number and expiration date. Some merchants can update automatically if they have your account on file, but many require you to do it manually. Check your subscriptions and automatic payments a few weeks before your expiration date so you don't miss a payment.

The difference between your card number and your account number

These are the same thing. The 16-digit number on your card is your account number. When your card expires and you get a replacement, you'll receive a new 16-digit number, even though it's the same account. This is a security measure — it limits how long a stolen card number can be used.

Your bank also has an internal account number that doesn't change. This is what they use internally to track your account history, credit limit, and payment record. You won't see this number on your card, and you don't need it for transactions. The 16-digit number is what matters for everyday use.

Keeping your numbers safe

Your 16-digit account number and expiration date are semi-public — you have to share them to make purchases. But treat them like you would a house key: don't leave them lying around, and only give them to merchants you trust. Never text them, email them, or read them aloud in public.

Your CVV is different. It should never leave your card except at the moment you're making a purchase. If a merchant asks you to email your CVV or write it down, that's a red flag — legitimate businesses never ask for it that way. Scammers often pose as your bank or a retailer and request your CVV over the phone or email. Your real bank will never ask for it.

Frequently Asked Questions

Do all credit cards have 16 digits?

Most do, but American Express cards have 15 digits. The structure is slightly different, but the principle is the same: the first digits identify the network and issuer, and the remaining digits are your account number. Diners Club and some other specialty cards may also vary.

What if I lose my card?

Call your bank immediately — the number is on your statement or their website. Your bank will cancel the card and mail you a replacement with a new 16-digit number. You won't be responsible for fraudulent charges made after you report it lost, as long as you report it promptly. Your account itself stays open.

Can someone use my card with just the 16-digit number?

In person, no — the card itself has to be physically present or the number has to be read from the chip or magnetic stripe. Online, they would need the 16-digit number, expiration date, and CVV. With just the account number alone, they can't complete most transactions, but they could try to use it for fraud, so report a compromised number to your bank right away.

Why does my new card have a different number if it's the same account?

Each physical card gets its own unique 16-digit number as a security measure. When your card expires or you request a replacement, the new card has a new number, even though your underlying account is the same. This limits the window of time a stolen number can be used and makes it harder for fraud to persist across multiple card cycles.

Is it safe to store my card number in my phone?

Most phones have secure digital wallet features (Apple Pay, Google Pay, Samsung Pay) that encrypt your card information and don't store the actual card number. Using these is safer than carrying the physical card. Storing the number as a photo, note, or in an unencrypted app is not safe — if your phone is lost or hacked, your card information is exposed.