Credit cards have 16 digits, arranged in four groups of four

A standard credit card issued by Visa, Mastercard, or Discover has 16 digits printed on the front. American Express cards have 15 digits instead. These numbers are not random — each digit or group of digits serves a specific purpose, from identifying the bank that issued the card to validating that the card number itself is real.

The 16-digit number is called the Primary Account Number, or PAN. It appears in two places on your card: embossed (raised) on the front and printed flat on the back. The digits are divided into four groups of four for readability, though the spaces between them are just formatting — the actual account number is one continuous string of 16 numbers.

Key Takeaways

  • Standard credit cards have 16 digits; American Express cards have 15 digits.
  • The first digit identifies the card network (Visa starts with 4, Mastercard with 5, Discover with 6, American Express with 3).
  • Digits 2 through 6 identify the bank or financial institution that issued the card.
  • The last digit is a check digit that validates the entire card number using a mathematical formula.
  • The middle digits (7 through 15) are your unique account number assigned by your bank.

What the first digit tells you

The first digit of your card number identifies the card network. This digit is called the Major Industry Identifier, or MII. For consumer credit cards, the pattern is straightforward: Visa cards start with 4, Mastercard cards start with 5, Discover cards start with 6, and American Express cards start with 3. This is why you can often tell what type of card someone has just by looking at the first number.

This first digit matters because it signals to merchants and payment processors which network will handle the transaction. When you swipe or insert your card, the payment terminal reads this digit first to route your transaction to the correct processor.

Digits 2 through 6: The issuer identification number

The second through sixth digits make up the Issuer Identification Number, or IIN. This five-digit code identifies the specific bank or financial institution that issued your card. For example, one IIN might belong to Chase, another to Bank of America, another to a credit union. The IIN tells payment processors which bank to contact to verify the transaction and move money.

The IIN is standardized across the industry and maintained by the card networks. This is why your bank's customer service number often appears on the back of your card — the IIN ensures that any merchant or processor can identify which bank issued your card and contact them if there is a problem.

Digits 7 through 15: Your account number

The middle nine digits (positions 7 through 15) are your unique account number. This is the part of your card number that your bank assigns to you. No other cardholder at your bank will have this exact sequence. These digits distinguish your account from every other account the bank has issued.

Your bank uses this portion of the number to look up your account in their system, check your balance, review your transaction history, and process payments. If you lose your card and get a replacement, your bank will issue you a new card with a different account number in this section, even though the IIN (digits 2–6) will remain the same because it is still the same bank.

The last digit: The check digit

The final digit (position 16 on most cards, position 15 on American Express) is called the check digit. This digit is calculated using a mathematical formula called the Luhn algorithm, which uses all the other digits on the card to generate a single number that validates the entire card number.

The check digit exists to catch typos and fraud. When you enter your card number online or over the phone, the payment processor runs the Luhn algorithm on the digits you provided. If the check digit does not match what the formula produces, the system knows the number is invalid — either you made a typing error or someone entered a fake number. This is why you cannot just guess a credit card number and have it work; the check digit will almost certainly be wrong.

Why American Express is different

American Express cards have 15 digits instead of 16, and the structure is slightly different. Amex cards start with 3 (making them straightforward to spot), and the IIN is four digits instead of five. The account number is eight digits, and the check digit is still the last digit. Despite the different length and structure, the Luhn algorithm still validates Amex card numbers the same way.

The reason for the difference is historical — American Express built its payment system independently and never adopted the 16-digit standard that Visa, Mastercard, and Discover use. When you see a 15-digit card number, you can be certain it is an American Express card.

What the digits do not tell you

The card number itself does not contain your name, address, expiration date, or security code. Your name is printed separately on the front of the card. Your expiration date and the three-digit security code (CVV) on the back are separate pieces of information stored by your bank but not encoded in the 16-digit number. This separation is intentional — it means that even if someone sees your card number, they cannot complete a transaction without also having the expiration date and security code.

The card number also does not encode your credit limit, interest rate, or account balance. These details are stored in your bank's database and linked to your account number, but they are not part of the physical card number itself.

Frequently Asked Questions

Can someone use my card if they only know the 16-digit number?

Not for most online or in-person transactions. They would also need your expiration date and the three-digit security code (CVV) on the back. For some older or international merchants, the card number alone might be enough, which is why you should treat your full card number as sensitive information even though it is printed on the front of your card.

Why are the digits printed twice on my card?

The raised (embossed) digits on the front are for imprint machines — older payment terminals that physically pressed the card onto a receipt to capture the number. The flat printed digits on the back are for modern card readers and for you to read easily. Both show the same 16-digit number.

Do debit cards have the same number of digits as credit cards?

Yes. Debit cards issued by Visa or Mastercard have 16 digits with the same structure. The first digit identifies the network, and the rest follows the same pattern. The only difference is that a debit card draws from your bank account rather than a line of credit.

What happens if I type my card number wrong?

The payment processor will reject it. The check digit validation catches most typos automatically. If you somehow enter a number that passes the check digit test but is not your actual card number, the transaction will fail when the processor tries to verify the account with your bank.

Is it safe to write down my card number?

Writing down your full card number, expiration date, and security code together is not recommended. If someone finds that paper, they have everything needed to make purchases. If you need to store your card information, use your bank's app or a password manager that encrypts the data.