A credit card number has 13 to 19 digits, with most cards using 16
The number on the front of your credit card is not random. Each digit serves a purpose, and the total length depends on the card network and issuer. Visa and Mastercard cards typically have 16 digits. American Express uses 15. Discover cards use 16. Some specialty cards or older cards may have 13 or 14 digits, though these are less common now.
The first digit or first few digits identify the card network — the company that processes the transaction. The digits that follow identify your bank or card issuer. The middle section identifies your account. The last digit is a check digit, calculated using a formula, that helps catch typos and fraud.
Key Takeaways
- Most credit cards have 16 digits, but Visa, Mastercard, Discover, and American Express each follow their own standard length.
- The first digit or digits tell you the card network; American Express cards always start with 3, Visa with 4, Mastercard with 5, and Discover with 6.
- The digits in the middle identify your specific bank account and are unique to you.
- The last digit is a check digit that validates the entire number using a mathematical formula called the Luhn algorithm.
- You should never share your full card number, expiration date, or CVV with anyone except a merchant you trust during a legitimate transaction.
Why card networks use different lengths
Each card network — Visa, Mastercard, American Express, and Discover — sets its own standard for card number length. Visa and Mastercard chose 16 digits. American Express chose 15. Discover uses 16. These choices were made decades ago when the networks were first designed, and changing them now would require updating millions of merchants' payment systems, so the standards have stuck.
The length matters because payment terminals and online checkout systems are programmed to expect a specific number of digits for each network. If you type a Visa number into a form that expects 15 digits, the system may reject it. This is one reason why the first digits of your card number are visible — they tell the system which network you are using before you finish typing.
What the first digits tell you
The first digit or first few digits of your card number identify the card network. This is called the Issuer Identification Number, or IIN. American Express cards always start with 34 or 37. Visa cards always start with 4. Mastercard cards start with 51 through 55, or 2221 through 2720. Discover cards start with 6011, 622126 through 622925, 644, 645, 646, 647, or 648.
You can use these first digits to figure out which network your card belongs to before you even look at the card itself. This is useful if you are troubleshooting a payment problem or trying to remember which card you used for a purchase. The network identifier is public information — it does not expose anything sensitive about your account.
How the middle digits identify your account
After the network identifier comes a section of digits that your bank uses to identify you and your account. This section is called the bank identification number, or BIN, though technically the BIN includes the first six digits of your card number. The exact breakdown varies by issuer, but roughly speaking, these digits tell the payment network which bank issued the card and which specific account it is linked to.
This is why two Visa cards from the same bank will have different middle digits — they belong to different accounts. And why a Visa from one bank and a Visa from another bank will have different digits in this section. The bank keeps this part of the number secret from you in most cases; you see it on your card, but you would not normally need to memorize it or type it separately.
The last digit is a check digit that catches errors
The final digit of your card number is not part of your account identifier. It is a check digit, calculated using a mathematical formula called the Luhn algorithm. This digit exists to catch typos and straightforward fraud attempts.
Here is how it works: a computer takes all the digits before the last one, applies the Luhn formula, and calculates what the last digit should be. If you type your card number into a form and make a mistake in one digit, the check digit will not match the formula, and the system will reject the number before it even tries to charge your card. This saves time and prevents failed transactions. It also means that a scammer who guesses random card numbers is unlikely to accidentally hit a valid number, because the check digit would be wrong.
You do not need to understand the Luhn formula to use your card. The point is that the last digit is a safety feature, not part of your account information.
Why you should not share your full card number
Even though the structure of your card number is not secret, your full card number is. If someone has your complete 16-digit number, your expiration date, and your CVV (the three-digit code on the back), they can make purchases online without your permission.
The first few digits are safe to share — merchants and payment processors need to see them to route your transaction to the right network. But you should never type or speak your full card number to anyone except a merchant you trust during a legitimate purchase. This includes customer service representatives, even if they call you claiming to be from your bank. Real banks will never ask for your full card number over the phone.
If you are concerned that your card number has been compromised, contact your bank when ready. They can cancel the card and issue you a new one. The new card will have a different number, different expiration date, and a different CVV, so old fraudulent charges cannot be repeated.
How card numbers differ across networks
| Network | Total Digits | Starts With |
|---|---|---|
| Visa | 16 | 4 |
| Mastercard | 16 | 51–55 or 2221–2720 |
| American Express | 15 | 34 or 37 |
| Discover | 16 | 6011, 622126–622925, 644–648 |
The differences in length and starting digits are historical. When these networks were created, they each chose a standard that made sense for their systems at the time. American Express chose 15 digits partly because it wanted a shorter number that was easier to remember and type. Visa, Mastercard, and Discover all settled on 16, which became the industry standard for most cards.
Some specialty cards — business cards, prepaid cards, or cards issued outside the United States — may have different lengths or starting digits. But if you are using a standard personal credit card from a major U.S. bank, it will follow one of the four patterns above.
Frequently Asked Questions
Is my card number the same as my account number?
No. Your card number is specific to the physical card in your wallet. Your account number is the underlying bank account that the card is linked to. If your card is lost or stolen and your bank issues you a replacement, you get a new card number, but your account number stays the same. The bank uses your account number to track your balance and payment history.
Can someone use my card number if they only have the first six digits?
No. The first six digits (the BIN) tell a merchant which network and bank issued your card, but they do not contain enough information to make a purchase. A scammer would need your full 16-digit number, expiration date, and CVV to charge your card online. In person, they would need the physical card itself.
Why does American Express use 15 digits instead of 16?
American Express chose 15 digits when it designed its card system, partly to make the number shorter and easier to remember. The company has stuck with that standard for decades. There is no technical reason why 15 is better or worse than 16; it is straightforward the choice American Express made, and changing it now would break compatibility with millions of merchants and payment systems.
What is the CVV, and how is it different from my card number?
The CVV (Card Verification Value) is a three-digit code on the back of your card, or four digits for American Express on the front. It is not part of your card number. The CVV is used to verify that you physically have the card when you make an online purchase. A merchant can see your card number in their system, but they should never store your CVV — it should be deleted after the transaction is complete.
If I memorize my card number, is that safer than carrying the card?
Memorizing your card number does not make it safer. If someone gains access to your card number through a data breach or by seeing you type it, they can use it regardless of whether you have memorized it. The safest approach is to keep your full card number, expiration date, and CVV private, and only enter them on find websites (those that start with https://) or with merchants you trust.