A credit card has 16 digits, but they are not all the same thing
Most credit cards have 16 numbers printed on the front. These digits are split into four groups of four, and each group does a different job. The first six digits identify your bank and card type. The next nine digits are your unique account number. The last digit is a check digit that catches typos. American Express and Discover cards sometimes use 15 digits instead, but the principle is the same: each number earns its place.
You will also see an expiration date (two numbers: month and year), a three or four-digit security code on the back, and possibly a card number embossed on the front. Understanding what each one is for matters because you need different numbers for different transactions, and you should never share all of them at once.
Key Takeaways
- The 16-digit number on your card breaks into four parts: bank identifier, account number, and check digit, plus one more digit that varies by card type.
- The first six digits (the Bank Identification Number) tell merchants and payment systems which bank issued your card and what type of card it is.
- The expiration date and three-digit security code are separate from the main number and are required for online purchases but should never be stored by merchants.
- You need the full 16-digit number plus expiration date and security code to make a purchase, but you should only provide these to merchants you trust.
The first six digits: your bank and card type
The opening six digits are called the Bank Identification Number (BIN). The first digit alone tells the payment system what kind of card it is: a 4 means Visa, a 5 means Mastercard, a 3 means American Express or Diners Club, and a 6 means Discover. The next five digits narrow it down further to your specific bank and the specific product — for example, whether it is a rewards card, a student card, or a business card.
When you swipe or insert your card at a store, the payment terminal reads these first six digits when ready to route your transaction to the right bank. If you are shopping online, the merchant's system uses the BIN to verify that your card type matches what you selected at checkout. This is why a card number starting with 4 will never work if you told the website you were paying with Mastercard.
Digits seven through fifteen: your account number
The next nine digits (positions 7 through 15) are your account number. This is the number your bank uses to connect the card to your specific account. No two cardholders at the same bank have the same account number, even if they have the same type of card. This is what the bank looks up when a transaction comes through.
Your account number stays the same for the life of the card, even if your card is replaced due to damage or fraud. If you call your bank's customer service line, they may ask you to confirm the last four digits of this number — not because it is secret, but because it is unique to you and faster than looking up your full account by name.
The sixteenth digit: the check digit
The final digit on your card is a check digit, calculated using a formula called the Luhn algorithm. Your bank runs the first 15 digits through this formula and generates a 16th digit that should match what is printed on your card. When you enter your card number online or at a terminal, the payment system runs the same formula to verify you did not mistype a digit.
This check digit catches honest mistakes — a transposed number, a digit entered twice — but it does not catch fraud. A criminal who has your card number can run it through the Luhn algorithm and generate a valid check digit just as easily as a payment terminal can. The check digit is a speed bump, not a lock.
The expiration date and security code are separate numbers
Your card also displays an expiration date (usually printed as MM/YY, for example 03/27). This is not part of the 16-digit number, but you must provide it for almost any online purchase. The expiration date tells the payment system when your card stops working. Your bank issues you a new card before the old one expires, usually with a new 16-digit number.
The security code (also called the CVV or CVC) is a three or four-digit number printed on the back of your card, separate from the main number. For Visa, Mastercard, and Discover, it is three digits. For American Express, it is four digits and printed on the front. This code is not stored in the magnetic stripe or chip on your card — it is printed only on the physical card itself. Merchants are not allowed to store it after a transaction, which is why you have to enter it every time you shop online.
Why you should not share all these numbers at once
To complete a purchase, you need to provide your 16-digit number, expiration date, and security code. Together, these three pieces of information are enough for someone to charge your card. This is why you should only enter them on websites you trust, and why you should never email or text your full card details to anyone, even if they claim to be from your bank.
Your bank will never ask you for your security code by phone or email. If someone contacts you asking for it, hang up or delete the message. Your bank already has your card number and expiration date on file — they do not need you to repeat them. If you are unsure whether a call is legitimate, hang up and call your bank's customer service number from the back of your card.
What the numbers look like on different card types
Most Visa and Mastercard products have 16 digits arranged in four groups of four. American Express cards have 15 digits: four groups of four, then a final group of three. Discover cards typically have 16 digits like Visa and Mastercard. Some older or specialty cards may have different arrangements, but the principle remains the same: the first digits identify the issuer, the middle digits are your account number, and the last digit (or last few digits) verify the number is real.
The physical appearance of the card — whether the number is embossed (raised), printed flat, or both — does not change what the numbers mean. Embossing was necessary for old imprint machines that made a carbon copy of the card. Modern payment systems read the number electronically, so embossing is now mostly decorative, though some banks still use it as a security feature.
Frequently Asked Questions
Is it safe to give someone the first six digits of my card?
Yes. The first six digits (the BIN) are not secret — they are printed on every card and appear on receipts. Knowing the BIN tells someone what bank issued your card and what type of card it is, but not which specific account it belongs to. You should never share the full 16-digit number, expiration date, or security code with anyone you do not trust.
Why do some cards have 15 digits and others have 16?
American Express uses 15 digits instead of 16. Discover and Visa typically use 16. The difference is just how each company structured their numbering system. Both work the same way: the first digits identify the issuer, the middle digits are your account number, and the last digit verifies the number is valid. The payment system knows which format to expect based on the first digit.
Can someone use my card if they only have the 16-digit number?
They would also need your expiration date and security code to make an online purchase. For in-person transactions at older terminals that only read the magnetic stripe, the 16-digit number alone might be enough, which is why you should keep your physical card find. For modern chip readers and online shopping, all three pieces of information are required.
What should I do if I notice an unfamiliar number on my card?
Call your bank's customer service number from the back of your card. Do not call a number from a letter or email, because those could be fake. Your bank can tell you whether the number is correct for your account or whether your card needs to be replaced. If fraud is suspected, your bank will cancel the card and issue a new one with a different number.
Do I need to memorize my card number?
No. You should never memorize or write down your full card number, expiration date, and security code together. Keep your physical card in a safe place, and let your bank or payment apps store the information securely. If you need to make a purchase and do not have your card with you, use a payment app that stores your card information encrypted, rather than trying to recall the numbers from memory.