The Luhn algorithm (mod-10) is a checksum formula that validates identification numbers. It doubles every second digit from the right, sums all digits, and checks if the result is divisible by 10.

Any number that uses Luhn validation: credit card numbers, IMEI numbers, Canadian SINs, various national ID numbers, and custom sequences. Enter any numeric string to check.

Enter your number without the check digit, select 'Generate Check Digit' mode, and click Calculate. The tool will compute the digit that makes the complete number valid.

Either the number has a typo, or it doesn't use Luhn validation. Not all numeric identifiers use Luhn—some use different checksum algorithms.

Yes, but our dedicated Credit Card Validator also detects card type and shows card-specific information. This tool is more general-purpose.

Each digit, whether it was doubled, the result after doubling (subtracting 9 if over 9), and the running sum. The final sum should be divisible by 10 for valid numbers.

All processing happens in your browser—nothing is sent to any server. However, avoid entering real credit card numbers in any online tool.

Yes. The tool strips all non-numeric characters before validation. Enter numbers in any format.

There's no strict limit, but Luhn is typically used for numbers between 8-19 digits. Very long numbers may have display issues.

Luhn catches all single-digit errors and most transpositions. It's highly effective for error detection but not designed for security or fraud prevention.

Luhn Calculator - Validate & Generate Check Digits

Input

Quick Examples

Related Tools

Result

Calculation Details

Step-by-Step Breakdown

Algorithm Explained

Related Tools