Credit card numbers have 13 to 19 digits, depending on the card type
Most credit cards you'll encounter have 16 digits. Visa, Mastercard, and Discover cards typically use 16 digits. American Express is the main exception — their cards have 15 digits. Some specialty cards and older cards may have 13 or 14 digits, and a small number of cards issued internationally can reach 19 digits, though this is rare in the United States.
The digits aren't random. They follow a specific structure that includes information about the card issuer, the account, and a security check built into the number itself. Understanding this structure can help you recognize whether a card number looks legitimate when you're entering it online or over the phone.
Key Takeaways
- Visa, Mastercard, and Discover cards have 16 digits; American Express has 15 digits.
- The first digit or first few digits identify the card network (Visa starts with 4, Mastercard with 5, American Express with 3, Discover with 6).
- The digits include the issuing bank's code, your account number, and a check digit that validates the entire number.
- You should never share your full card number with anyone except the merchant or bank you're paying directly.
How the digits break down on a standard 16-digit card
The first digit is the Major Industry Identifier (MII). For credit cards, this is almost always 3, 4, 5, or 6. Visa cards start with 4, Mastercard with 5, American Express with 3, and Discover with 6. This single digit tells the payment system which network to route your transaction through.
The next five to seven digits make up the issuer identification number (IIN), also called the bank identification number (BIN). This identifies which bank or financial institution issued your card. If you call your bank's customer service number from the back of your card, they use these digits to pull up your account when ready.
The remaining digits (up to the last one) form your account number. This is unique to you within your bank's system. The very last digit is a check digit, calculated using a mathematical formula called the Luhn algorithm. This digit allows payment systems to catch typos or fraud attempts — if someone enters your card number with even one digit wrong, the check digit won't match, and the transaction will be rejected.
Why American Express is different
American Express cards have 15 digits instead of 16. The structure is similar — the first digit identifies it as American Express (always 3), the next two digits narrow down which type of Amex card it is, and the remaining 12 digits are the account number and check digit.
American Express also prints four digits on the front of the card (called the Amex identifier) in addition to the full 15-digit number on the back. This four-digit code is sometimes used as an extra security measure when you're making purchases online or over the phone, though it's different from the three-digit CVV code that Visa and Mastercard use.
Where you'll see the card number
On Visa, Mastercard, and Discover cards, the full 16-digit number is printed on the front of the card, usually in raised digits or embossed text. On American Express cards, the 15-digit number appears on the back of the card, not the front.
When you enter your card number online, you're typing these same digits into a payment form. When you swipe or insert your card at a store, the card reader captures this number electronically. The number itself is what identifies your account to the payment network, so protecting it is important — never photograph it, email it, or share it with anyone except the business you're paying directly.
What the check digit actually does
The last digit of your card number isn't part of your account identifier — it's a built-in error detector. Banks and payment processors use the Luhn algorithm to verify that the number is mathematically valid before they even attempt to process a transaction.
Here's why this matters: if you mistype one digit when entering your card number online, the check digit won't match the rest of the number, and the payment system will reject it when ready. You won't be charged, and you'll know to re-enter the number. This catches honest mistakes before they become problems. It also makes it harder for someone to guess a valid card number — they can't just try random combinations, because most won't pass the check digit test.
Older cards and international variations
Diners Club cards, which are less common in the United States but still issued, typically have 14 digits. JCB cards, another international network, usually have 16 digits. If you're traveling or using a card issued outside the US, you might encounter a card with a different digit count, but 15 or 16 digits covers the vast majority of cards you'll use domestically.
Some very old cards or specialty cards (like certain corporate or prepaid cards) may have 13 digits. If you're unsure whether a card number you're looking at is legitimate, the digit count is one quick check — if it's fewer than 13 or more than 19, something is wrong.
Frequently Asked Questions
Is my card number the same as my account number?
No. Your card number includes your account number, but it also includes the bank identification code and the check digit. Multiple cards can be linked to the same bank account, and each card gets its own unique 16-digit number. If you lose a card, the bank issues a new card with a new number, even though it's still the same account.
Can someone use my card if they only know the first few digits?
No. The first digits identify the card network and bank, but they don't identify your specific account. Someone would need the full card number, expiration date, and CVV code to attempt a transaction. Never share your full card number with anyone you don't trust completely.
Why do some websites ask for only the last four digits?
The last four digits are unique enough to identify which card you're using without exposing your full number. Banks and payment processors use this as a security practice — they can confirm you're using the right card without storing or transmitting your complete card number through multiple systems.
What if my card number has a different digit count than I expected?
Check the card network. American Express has 15 digits, while Visa, Mastercard, and Discover have 16. If your card has a significantly different count, contact your bank to confirm it's legitimate. Some specialty cards or international cards may vary, but your bank can tell you whether the number is correct.