Luhn Checker

The mod 10 checksum behind card numbers and IMEIs. Everything runs in your browser and nothing is sent anywhere.

Try a published test number: 79927398713 Visa test Mastercard test one digit off

How it works

1. Start from the rightmost digit and move left.
2. Double every second digit (highlighted). If the result is more than 9, subtract 9.
3. Add everything up. The number is valid when the total is a multiple of 10.