What Do Credit Card Numbers Mean [Explained]

Credit card numbers aren’t arbitrary. They follow a specific structure designed by the International Organization for Standardization (ISO) in the ISO/IEC 7812 standard. Every digit or group of digits in your credit card number provides essential information.

1. Major Industry Identifier (MII):

This is the very first digit of your credit card number. The MII is a system created by the ISO that classifies the card’s industry. Here are the categories:

  • 0: ISO/TC 68 and other industry assignments
  • 1: Airlines
  • 2: Airlines, financial and other future industry assignments
  • 3: Travel and entertainment
  • 4, 5: Banking and financial
  • 6: Merchandising and banking/financial
  • 7: Petroleum and other future industry assignments
  • 8: Healthcare, telecommunications and other future industry assignments
  • 9: For assignment by national standards bodies

So, for most credit cards, which belong to the banking and financial industry, this number will be a 4 or 5.

2. Issuer Identification Number (IIN):

The first six digits of the card number (including the MII) comprise the IIN, also known as the Bank Identification Number (BIN). This set of digits identifies the specific institution that issued the card. Certain numbers are associated with specific card issuers:

  • Visa cards start with 4
  • Mastercard numbers begin with 51 through 55
  • Discover cards start with 6011 or 65
  • American Express cards start with 34 or 37

3. Account Number:

Following the IIN, the next sequence of digits (usually up to the 15th digit on a 16-digit card) is the individual account identifier. This number is tied to the cardholder’s specific account with the issuer. When you look at multiple cards from the same issuer, you’ll notice the first six digits (the IIN) are the same, but these middle digits will vary from card to card.

4. Check Digit:

The final digit of a credit card number is known as the check digit. Its purpose is to verify the accuracy and authenticity of the credit card number, ensuring it hasn’t been entered incorrectly or fraudulently. The check digit is calculated using the Luhn Algorithm, which is a checksum formula for error detection.

Let’s look at a hypothetical 16-digit Visa card number to illustrate these points:

4123 4567 8901 2345

  • The first digit, 4, indicates this is a card from a banking or financial institution (MII).
  • The first six digits, 412345, identify the specific issuing institution (IIN).
  • The next nine digits, 678901234, identify the individual’s unique account number.
  • The final digit, 5, serves as a check digit, verifying the card number’s accuracy and authenticity.




1. What do the digits on my credit card number mean?

Every digit in your credit card number has a specific purpose. The first digit represents the Major Industry Identifier (MII), which indicates the card’s industry sector. The next 5 digits along with the MII make up the Issuer Identification Number (IIN), identifying the institution that issued the card. The subsequent digits up to the second last digit represent your personal account number, and the final digit is a check digit to validate the credit card number.

2. Are all credit card numbers the same length?

Most credit cards have 16 digits, but this isn’t always the case. American Express cards typically have 15 digits, and some cards, like certain versions of Diner’s Club cards, have 14 digits. It’s also possible to encounter cards with up to 19 digits.

3. How does the check digit on my credit card work?

The final digit of your credit card number is the check digit, which validates the rest of the credit card number. It’s calculated using the Luhn algorithm, a simple checksum formula. This digit helps to catch any accidental errors when the card number is manually entered, and provides a first line of defense against fraudulent card numbers.

4. Do different credit card companies use different IINs?

Yes, different credit card companies start their card numbers with different digits. For instance, Visa cards start with a 4, Mastercards start with numbers between 51 and 55, and American Express cards start with 34 or 37.

5. Can I determine my credit limit or card type based on my credit card number?

No, the credit card number itself doesn’t contain information about your credit limit or the specific card product. It mainly identifies the card issuer and your unique account with the issuer. Information like your credit limit or card benefits is managed separately by the credit card company.

6. Can someone steal my identity using my credit card number?

If someone unauthorized has access to your credit card number, they could potentially make fraudulent charges on your account. However, most card issuers have robust security measures in place to detect and prevent such activity. If you ever suspect your card number has been compromised, contact your credit card issuer immediately.


7. What is a CVV and where can I find it on my credit card?

The Card Verification Value (CVV), sometimes referred to as Card Security Code (CSC) or Card Verification Code (CVC), is a security feature for ‘card not present’ transactions. It’s typically a three-digit number (four digits for American Express) on the back of your card, separate from the card number. This number provides a cryptographic check of the information embossed on the card, offering another layer of security against fraud.

8. Is the credit card number linked to my personal information?

Your credit card number is linked to your account with the credit card issuer, which will have your personal information on file. However, the card number itself doesn’t contain personal information like your name, address, or Social Security number. That said, if someone unauthorized gains access to your credit card number, they could potentially use it for fraudulent transactions, so it’s essential to keep your card details secure.

9. What happens if my credit card number is compromised?

If you suspect your credit card number has been compromised, the first thing you should do is contact your credit card issuer. They can block your card to prevent further fraudulent transactions and issue you a new card with a new number. Many credit card issuers offer zero-liability policies, meaning you won’t be held responsible for unauthorized transactions if you report them promptly.

10. Why are credit card numbers on the front of the card, but the CVV is on the back?

This arrangement is another security measure. If your card is physically stolen and the thief is using it for ‘card present’ transactions, they’d obviously have access to both numbers. However, for ‘card not present’ transactions (like online shopping), if someone only sees the front of your card or gets your card number some other way, they wouldn’t have the CVV. This makes it harder for them to complete transactions without your authorization.

11. What should I do if I forget my credit card number?

If you’re making an online transaction and don’t have your card on hand, you can usually find your card number by logging into your credit card account on your issuer’s website or app. Remember, it’s important to keep your login details secure and not to access your account on public computers or unsecured public Wi-Fi networks. If you can’t find your card number, contact your credit card issuer for help.