When you enter your card details to add it to your account and you write 1 number wrong, it instantly tells you that the card is wrong. How do they know?
In: Technology
Credit Card numbers are generated with something called the Luhn algorithm. It is a checksum algorithm. It takes the 15 real digits of your credit card and determines the 16th.
This means that only one final digit is valid, and 9 are invalid. If you type a number in wrong, it will definitely fail the checksum.
The algorithm also counts every second digit differently (they’re doubled). This means that simply swapping digits also causes a failure, which is the most common type of error when typing a card number.
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