Credit cards, or plastic money, have changed commerce and transactions. Everyone has at least one, emblazoned with pictures or scenery or just the bank's name, a magnetic strip on the back and a chip on the front. Some people may even have memorized the numbers of their credit cards!
Of course with the convenience of credit cards comes the fraud schemes. So how can you quickly tell if a card is fake or real without actually trying to process a transaction (or if your payment processor's systems are down)?
Those 15 or 16 numbers on the card mean something. Here's how to crack the code:
Let's use this number (16 digits): 4417 1234 5678 9113
The first digit, 4, is the Major Industry Identifier (MII). It identifies the entity that issued the card.
1 and 2 are issues by Airlines
3 is Travel and Entertainment
4 and 5 Financial and Banking
6 is Banking and Merchandise
7 is Petroleum (Gas cards)
8 is Telecommunications
9 is a national assignment
In our sample number, the MII is 4, indicating a bank or financial institution.
The first 6 digits are the Issuer ID Number (IIN, but includes MII). It identifies the institution that issued the card.
Amex: 34xxxx & 37xxxx
Mastercard: 51xxxx - 55xxxx
Visa: 4xxxxx
Discover: 6011xx, 644xxx, 65xxxx
The next 7 digits, not including the last digit of the card, are the card holders account number. Many cards will use 9 digits to indicate account numbers.
The last digit is a checksum or a check digit. Using the Luhn algorithm, it's used to validate the credit card number. Here's how to apply the Luhn algorithm to our number to validate it:
Take our sample number (or even one of yours), 4417 1234 5678 9113, and DOUBLE every OTHER digit, from the RIGHT. So,
1x2 9x2 7x2 5x2 3x2 1x2 1x2 4x2
You'd get: 8 2 2 6 10 14 18 2
Take these digits and ADD them to the UNDOUBLED digits (4 7 2 4 6 8 1 3). So,
8+4+2+7 + 2+2+6+4 + 1+0+6+1+4+8 + 1+8+1+2+3
(All the double digits numbers are added as a SUM of their digits, so 14 become 1+4 and 18 becomes 1+8)
From that, we get: 70
If the final SUM is divisible by 10, the card number is valid. If it's not, it's fake or invalid.
Try it on one of your own cards!