What is the Luhn Algorithm?
The Luhn algorithm, also known as the mod 10 algorithm, is a simple checksum formula used to validate a variety of identification numbers, most notably credit card numbers. It's designed to protect against accidental errors, such as mistyping a card number, and is widely used in the financial industry.
How to Test a Credit Card Number with the Luhn Algorithm
- Start from the rightmost digit.
- Double every second digit from the right. If the result is a two-digit number, add the digits together.
- Sum all the digits.
- If the total modulo 10 is 0, the number is valid.
Example
Let's take the credit card number 4111111111111111 as an example.
- Starting from the rightmost digit, double every second digit: 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1.
- Double the second, fourth, sixth, eighth, and tenth digits: 2, 2, 2, 2, 2, 2, 2, 2, 2, 2.
- Sum all the digits: 4 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 = 60.
- The total modulo 10 is 0, so the number is valid.
Why Use the Luhn Algorithm?
The Luhn algorithm is an effective tool for validating credit card numbers because it can quickly identify common errors in data entry, such as transposed digits or an incorrect card number. This helps prevent fraudulent transactions and ensures the security of financial transactions.