Introduction

The Luhn algorithm is a simple checksum formula used to validate a variety of identification numbers, most notably credit card numbers. This guide will show you how to test credit card numbers with the Luhn algorithm using a real-world example.

luhn algorithm verification test

What is the Luhn Algorithm?

The Luhn algorithm, also known as the mod 10 algorithm, is a method for detecting errors in identification numbers, primarily credit card numbers. It's used to ensure that the numbers have been correctly entered and processed.

luhn algorithm test example

Step-by-Step Luhn Algorithm

To validate a credit card number using the Luhn algorithm, follow these steps:

luhn algorithm test example

  1. Start from the rightmost digit.
  2. Double every second digit from right to left (beginning with the second digit from the right).
  3. If doubling of a number results in a two-digit number, add the digits together (e.g., 8 doubled is 16, add 1 + 6 to get 7).
  4. Sum all the digits.
  5. If the total modulo 10 is equal to 0, then the number is valid according to the Luhn algorithm.

Example

Let's take the credit card number 4111111111111111 and validate it with the Luhn algorithm.

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  1. Starting from the rightmost digit, double every second digit from right to left: 4, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1.
  2. Double 4, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 (4 becomes 8, 1 becomes 2, and so on): 8, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2.
  3. Add the digits together: 8 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 = 30.
  4. The total modulo 10 is 0, so the credit card number 4111111111111111 is valid.

Conclusion

Validating credit card numbers with the Luhn algorithm is a straightforward process. By following this guide and using the provided example, you can easily test the validity of credit card numbers and improve the security of your transactions.