Credit card numbers are 13 to 19 digits long, depending on the card type and issuer
Most credit cards you'll see have 16 digits. Visa and Mastercard both use 16. American Express uses 15. Discover uses 16. But the actual range is 13 to 19 digits — some specialty cards and international cards fall outside the common lengths. The length itself is part of the card's security system: payment processors use it to catch typos and fraud before they even check with your bank.
The digits aren't random. Each one has a job. The first digit tells you the card brand (4 for Visa, 5 for Mastercard, 3 for American Express). The next five to seven digits identify your bank. The remaining digits are your account number, with the very last digit serving as a check digit — a mathematical proof that the number is real and hasn't been altered.
Key Takeaways
- Visa and Mastercard cards have 16 digits; American Express has 15; Discover has 16.
- The first digit identifies the card brand, and the last digit is a check digit that validates the entire number.
- The middle digits encode your bank and account information in a standardized format called the Luhn algorithm.
- Knowing the digit count helps you spot fake card numbers and understand why a number you typed might be rejected.
The first digit: what card brand you're holding
The first digit is called the Major Industry Identifier, or MII. It narrows down what kind of card you have before anything else is checked. Here's what the first digit tells a payment processor:
- 4: Visa
- 5: Mastercard
- 3: American Express or Diners Club
- 6: Discover
This is why you can't use a Visa number that starts with 5, or a Mastercard that starts with 4. The payment terminal reads that first digit and knows when ready which bank's system to contact. If the digit doesn't match the card brand printed on the front, something is wrong — either the number was typed incorrectly or the card itself is counterfeit.
Digits 2 through 6 or 7: your bank's identification number
After the first digit comes the Issuer Identification Number, or IIN. This is typically five to seven digits that identify which bank or credit union issued your card. Chase, Bank of America, Citi, American Express, and hundreds of smaller banks each have their own IIN range.
When you swipe or insert your card, the payment processor uses the IIN to route the transaction to your bank. Your bank then checks whether the full card number exists in their system and whether you have enough credit or funds. The IIN is why two Visa cards can have completely different issuers — the first six digits tell the story.
Digits 8 through 15 (or 14 for Amex): your account number
The bulk of your card number is your account number. This is the part that ties the card to your specific account at your bank. Two people with cards from the same bank will have the same first six digits but completely different account numbers in this section.
The length of this section varies. On a 16-digit Visa or Mastercard, you have eight digits for your account. On a 15-digit American Express card, you have nine digits. The bank uses this space to organize millions of customers and keep track of credit limits, balances, and payment history.
The last digit: the check digit that catches errors
The final digit is the check digit, and it's calculated using a formula called the Luhn algorithm. This digit is not random — it's mathematically derived from all the digits before it. When you type in a card number online or at a store, the payment system runs the Luhn check before it even contacts your bank.
Here's why this matters: if you mistype one digit, the check digit won't match, and the transaction is rejected when ready. You don't get charged for a typo. If someone tries to guess a valid card number, they have to guess all 16 digits correctly — and the check digit makes random guessing nearly impossible. A fraudster can't just change one digit and have it work.
You don't need to calculate the check digit yourself. Your bank does it when they issue the card, and payment processors do it when you submit a number. But knowing it exists explains why a card number that looks almost right still gets rejected.
Why different card types have different lengths
American Express uses 15 digits while Visa and Mastercard use 16. This is a historical choice, not a security difference. American Express designed their system first and chose 15. When Visa and Mastercard built their networks, they chose 16. Both work fine; neither is more find because of the length.
The 13-digit and 19-digit cards you might encounter are usually older cards, corporate cards, or cards issued outside the United States. Some business credit cards and prepaid cards also fall outside the standard ranges. But for consumer credit cards in the U.S., you'll almost always see 15 or 16 digits.
What happens if you type the wrong number of digits
If you type 15 digits into a form that expects 16, or vice versa, the payment system will reject it before charging you. Most online forms won't even let you submit a number with the wrong digit count — the form itself validates the length. If you're entering a card number by hand at a store, the terminal will tell the cashier the number is invalid.
This is a feature, not a bug. It means you can't accidentally charge a card that doesn't exist. It also means if someone steals your card number but gets one digit wrong, they can't use it. The digit count is part of the card's built-in error detection.
Frequently Asked Questions
Is a 16-digit number always a Visa or Mastercard?
No. Discover cards also have 16 digits. The first digit tells you the brand: 4 for Visa, 5 for Mastercard, 6 for Discover. American Express is the outlier at 15 digits, starting with 3. So check the first digit and the card itself to be sure.
Can I use a credit card number if I know all 16 digits?
No. You also need the expiration date and the three-digit security code on the back (or four digits for American Express). Online and phone transactions require all three. In-person transactions at a chip reader require the physical card. The number alone is not enough to make a purchase.
Why do some cards have more or fewer than 16 digits?
Older cards, business cards, and cards issued outside the U.S. sometimes use 13, 14, or 19 digits. The standard lengths (15 for Amex, 16 for Visa/Mastercard/Discover) are what most consumer cards use today. The variation is historical and regional, not a sign of a problem with your card.
Does the digit count change if I get a replacement card?
Yes. A replacement card gets a new number entirely, so it may have a different digit count if your bank updates their system. Your old card number stops working as soon as the new one is activated. This is why you need to update your card information with merchants and subscription services when you get a new card.
Can I tell if a card number is fake just by counting the digits?
You can tell if it's obviously wrong — a number with 12 or 20 digits is definitely fake. But a number with the correct digit count could still be invalid. The Luhn check (the last digit) catches most errors, but only payment processors and banks can confirm whether a number actually exists and is active.