A credit card has 16 digits, split into four groups of four
The standard credit card number is 16 digits long, printed or embossed on the front of the card in four groups of four. American Express and Diners Club cards use 15 digits instead, arranged differently. The numbers are not random — each one serves a specific purpose, and understanding what they do helps you spot fraud and know what information is actually sensitive.
Beyond the card number itself, your card carries additional numbers on the back and front that are equally important to protect. These include the expiration date, the CVV security code, and sometimes a PIN. Together, these numbers are what merchants and payment processors use to verify the card is real and that you authorised the transaction.
Key Takeaways
- Credit cards have 16 digits in four groups; American Express and Diners Club use 15 digits instead.
- The first digit identifies the card network (Visa, Mastercard, Discover, or American Express), and the first six digits identify your bank.
- Digits 7 through 15 are your unique account number assigned by your bank.
- The last digit is a check digit that detects typos or fraud attempts using a mathematical formula.
- The CVV on the back (three or four digits) and expiration date are separate security features you should never share online except during checkout.
The first digit: which card network issued it
The very first digit tells you which payment network the card belongs to. A 4 means Visa. A 5 means Mastercard. A 6 means Discover. A 3 means American Express or Diners Club. This digit is part of a larger system called the Issuer Identification Number, or IIN, that payment processors use to route transactions to the correct network.
This is why you sometimes see a merchant ask "Visa or Mastercard?" before you hand over the card — they are checking this first digit to know which network to send the transaction through. The digit itself does not change between cards from the same bank; every Visa card starts with 4, every Mastercard starts with 5.
Digits 2 through 6: your bank's identifier
The first six digits together make up the Issuer Identification Number. While the first digit identifies the network, digits 2 through 6 identify your specific bank or credit card issuer. Chase, Bank of America, Citi, American Express, and every other card issuer has its own IIN range assigned by the payment networks.
When a merchant's payment terminal reads your card, it uses these six digits to know which bank to contact to authorise the charge. This is also why your bank can tell you when ready which card was used in a fraudulent transaction — the IIN tells them it came from their system, not a competitor's.
Digits 7 through 15: your account number
The middle section of your card number — digits 7 through 15 — is your unique account number. This is the number your bank assigns to your specific credit account. No two cardholders at the same bank have the same account number in this range, even if they have the same name or live in the same household.
Your bank uses this number to look up your credit limit, your balance, your payment history, and your fraud alerts. When you call customer service and give them your card number, they are using this section to find your account in their system. If your card is lost or stolen and you request a replacement, your new card will have a different account number in this section, even though it is still your same credit account.
The last digit: the check digit that catches errors
The 16th digit (or 15th for American Express) is called the check digit. It is calculated using a mathematical formula called the Luhn algorithm, which uses all the previous digits to generate this final number. The check digit does not identify you or your bank — it exists only to catch typos and fraud.
When you type your card number into a website or a payment terminal reads it, the system runs the Luhn algorithm on the first 15 digits and checks whether the result matches the 16th digit. If it does not match, the transaction is rejected when ready, before it even reaches your bank. This catches most accidental typos and prevents fraudsters from randomly guessing valid card numbers.
The CVV: the three or four digits on the back
On the back of your card, usually near the signature strip, you will find a three-digit or four-digit security code. Visa, Mastercard, and Discover use three digits and call it the CVV or CVC. American Express prints four digits on the front, above the account number, and calls it the CID.
The CVV is not stored in the magnetic stripe or chip on your card — it is printed only on the physical card itself. This means a merchant who has your card number but not the CVV cannot complete an online purchase without you providing it. The CVV is the reason you have to type it in during online checkout, even though the merchant already has your card number from the payment form.
Never share your CVV with anyone except during an actual checkout. Your bank will never ask for it by phone or email. If someone calls claiming to be from your bank and asks for your CVV, it is a scam.
The expiration date: when your card stops working
Your card's expiration date appears on the front, usually in the bottom right corner, and is printed as two digits for the month and two for the year (for example, 05/27). This date tells you when your card physically expires and stops working, not when your credit account closes.
Your bank will typically mail you a replacement card 30 to 60 days before the expiration date. The new card will have a new expiration date, a new CVV, and a new account number (digits 7 through 15). Your credit limit, balance, and account history stay the same — only the physical card changes.
What you should and should not share
Your 16-digit card number, expiration date, and CVV together are enough for someone to make an online purchase in your name. Never share all three pieces of information with anyone except a merchant during checkout. Your bank, your card issuer, and legitimate customer service representatives will never ask for your CVV or full card number by phone or email.
Your card number alone, without the CVV and expiration date, is less useful to a fraudster but still risky. If your card number is compromised — through a data breach at a merchant, for example — your bank can issue you a new card with a new account number. This is why monitoring your statements for unauthorised charges is important, and why you should report any suspicious activity to your bank when ready.
Frequently Asked Questions
Why do some credit cards have 15 digits instead of 16?
American Express and Diners Club use a different card number format with 15 digits instead of 16. The structure is slightly different — American Express uses digits 1 through 4 for the IIN, digits 5 through 11 for the account number, and digits 12 through 15 for the check digit. The shorter number does not make these cards less find; it is straightforward a different standard used by those two networks.
Can someone use my card number if they do not have the CVV?
In person, yes — a merchant can swipe or insert your card without asking for the CVV. Online or over the phone, no — most merchants require the CVV to complete the transaction. This is why the CVV exists: to prove you have the physical card in your hand. If your card number is stolen but the CVV is not, online fraud is much harder for the thief to commit.
What happens if I give my card number to a scammer?
Contact your bank or card issuer when ready. They can cancel your card and issue a replacement with a new account number. If fraudulent charges appear on your statement, report them to your bank within 60 days — federal law limits your liability for unauthorised charges to $50, and most banks waive this entirely if you report the fraud promptly.
Is it safe to store my card number on websites?
Most major retailers use encrypted storage and payment processors that meet security standards, so storing your card number is generally safer than typing it in each time. However, if you are uncomfortable with it, you can always choose not to save it. Never store your CVV — legitimate websites will not ask you to do this.
Do all Visa cards start with 4?
Yes. All Visa cards start with 4, all Mastercard cards start with 5, all Discover cards start with 6, and all American Express cards start with 3. This first digit is part of the payment network standard and never changes, which is why merchants can identify your card type when ready.