Ever wondered how your bank, the Internet, ATM machines validate your cards? Well, it's not rocket science. It's pretty basic and now let me explain with an example.

Example Card Number: 4417 1234 5678 9113

The First Digit: this is the Major Industry Identifier. It designates the category of entity which issued the card.

• 1 & 2 are Airlines
• 3 is Travel and Entertainment
• 4 & 5 are Banking and Financial
• 6 is Merchandising and Banking
• 7 is Petroleum
• 8 is Telecommunication
• 9 is a National assignment

The First Six Digits: these are the Issuer Identification Number. It will identify the institution that issued the card.

Visa: 4xxxxx
MasterCard: 51xxxx – 55xxxx
Discover: 6011xx, 644xxx, 65xxxx
Amex: 34xxxx, 37xxxx

Cards can be looked up by their IIN. A card that starts with 376211 is a Singapore Airline Krisflyer American Express Gold Card. 529962 designates a pre-paid Much-Music MasterCard.

The Seventh & Following Digits: excluding the final digit, these are the persons account number. This leaves a trillion possible combinations.

The Final Digit: this is the check digit or checksum. It is used to validate the credit card number using the Luhn algorithm.

How To Validate A Credit Card With Your Mind
• Take the credit card number(let's use the example above).
4417 1234 5678 9113
• Double every other digit from the right.
(4x2)4(1x2)7 (1x2)2(3x2)4 (5x2)6(7x2)8 (9x2)1(1x2)3
• Add these to the undoubled digits
8+4+2+7 + 2+2+6+4 + 1+0+6+1+4+8 + 1+8+1+2+3 = 70
• If the final sum is divisible by 10, then the credit card number is valid. If it's not divisible by 10, the number is invalid or fake. Try it and see.