27 July, 2010
The Anatomy of a Credit Card Number
I've been wondering exactly how those digits on your credit card are constructed. Through an errant google search, I accidentally found the answer, with source code!.
The first digit describes the type of issuing institution (e.g., 1 for airlines, 4 for a bank, 7 for an oil company)
The next six digits describe exactly the issuer of the card. This could be your bank, or an airline. So, any credit card from chase will always have the same 6 digits.
The seventh to next to last digit is your account number, unique to your card.
The last digit is special. It's kind of verification number. The value of this number is calculated using a special algorithm using all the previous digits, just to make sure the number isn't bogus.
