Take a look in your wallet. Chances are you have a plastic (or, if you’re super fancy, metal) card with a 15- or 16-digit sequence of numbers on it. That’s your credit card number—or debit card number, if your card draws from your bank account and not a line of credit.
But what’s the point of credit card numbers? Are they sequential or random? Here’s what you need to know about credit card numbers:
What Is a Credit Card Number?
A credit card number is a unique number that helps identify your account and card. This number makes it possible for you to pay with the card and for money to be taken out of the right account.
Think about it similarly to your checking account number. Your personal checks are printed with a specific series of numbers. First, the routing number, which indicates which bank the check draws on. Next is the account number, which tells which account the money should come from.
Credit card numbers work the same way. Each part of that long number has a specific function. These are standardized by the International Organization for Standardization.
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The Meaning Behind Credit Card Numbers
The first number indicates which type of card it is. This is the Major Industry Identifier (MII). Visa card numbers, for example, always start with a 4. Here’s the breakdown:
- 3: American Express or cards under the Amex umbrella
- 4: Visa
- 5: Mastercard
- 6: Discover
That first digit along with the next five in the credit card number are called the Issuer Identification Number or Bank Identification Number. This identifies the credit card company and its network, similar to the bank routing number on a personal check. The ISO has issued a mandate to increase the IIN from six digits to eight digits to prevent a shortage.
The rest of the digits in your credit card number, with the exception of the final number, are related to your specific account. They aren’t necessarily the same numbers that appear in the account number on your statement. But this string of numbers is tied to your account so that payment processes use the right account when you make a credit or debit card payment.
The last digit of a credit card number is known as the check digit, determined by the Luhn algorithm. This number is applied in an unusual formula that helps determine if your credit card number is valid when you enter it. Using this formula, it takes only a fraction of a second for a computer to confirm that a credit card number is valid.
How to Tell If a Credit Card Number Is Valid
You, too, can crack the credit card code to see if the number you’re looking at is a valid one, if you really want to. Simply apply the Luhn algorithm. You can try this with your own credit card number.
- For 16-digit numbers, start with the first number on the left. For 15-digit numbers, start with the second digit.
- Double each alternating number on the card.
- Add any double-digit numbers so that they reduce to a single-digit number. For example, if one of the numbers is 8, it doubles to 16. You add 1 + 6 to get 7.
- Next, add all those numbers together with the alternating numbers that you did not double.
- If the total you get is divisible by 10, the credit card number is likely valid.
Let’s say your credit card number is 1234567890123456.
Since it’s a 16-digit number, we’ll start by doubling the first digit, adding it to the next digit, doubling the third digit, adding it to the fourth digit, and so on. When we double numbers like 5, we have to reduce the double digit down to the sum of the two digits—5 times 2 is 10, and 1 plus 0 is 1. So we end up with this:
2 + 2 + 6 + 4 + 1 + 6 + 5 + 8 + 9 + 0 + 2 + 2 + 6 + 4 + 1 + 6 = 58
Because 58 is not divisible by 10, it’s likely not a valid credit card number!
What Is a CVV Number?
Flip your credit card over and you’ll see a three-digit number on the back near or on the signature space. This is the Card Verification Value number. The CVV on American Express cards are often four digits found on the front of the card.
This is not part of the credit card number, but it’s often used to validate payments. When you’re making a card payment via phone or online, the vendor doesn’t have physical access to the card. To help ensure that you do have the card in your possession and aren’t simply trying card numbers generated using the math above, you have to enter the CVV number.
What Do the Last Four Digits of a Credit Card Mean?
The last four digits of your credit card number actually don’t mean much, but there’s a reason you might be asked for them. If you save a credit card in an online account or other database, the information has to be encrypted. Employees with that company can’t just look up accounts and see full credit card information. They’re usually only able to see the last four digits.
You might be asked to confirm those numbers to ensure the right card is being charged. You might also be asked to confirm them when buying something online with a saved card number to ensure you’re really you and not someone who has hacked into an account.
Why Does This Matter?
While this system is very important to credit card issuers and merchants, it actually matters very little to the average credit card user. You will always want to protect your credit card number from being stolen, and it might be helpful to know that the first six digits are the same for everyone with the same kind of credit card you have.
As credit cards continue to evolve, the EMV smart chips embedded on the cards will eventually replace magnetic strips as a means of transmitting credit card account numbers and verifying transactions. But the credit card number itself should still be with us for a long time.
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