How does the Luhn algorithm work for credit card validation?

The Luhn algorithm doubles every second digit from right to left. If doubling exceeds 9, 9 is subtracted. All resulting digits are summed, and if the total modulo 10 is 0, the number is valid.

Which cards use the Luhn algorithm?

The Luhn algorithm is an international standard (ISO/IEC 7812) used by almost all card networks: Visa, Mastercard, Mir, American Express, UnionPay, and JCB.

Does the Luhn check guarantee a real bank card?

No, Luhn validation verifies only mathematical checksum accuracy to prevent typos. Card validity and account status can only be verified by the issuing bank.

Luhn Calculator

Online Validator & Step-by-Step Luhn Solver

Enter a card number to see a detailed real-time mathematical breakdown of the checksum according to the Luhn formula.

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Card Number Verification

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Step-by-Step Solution by Luhn Algorithm:

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Luhn Generator

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How does the Luhn Algorithm work?

The Luhn algorithm is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers (Visa, MasterCard, Mir, etc.), insurance numbers, and membership cards. It was created by IBM scientist Hans Peter Luhn in 1954.

Mathematical Steps of the Formula:

From the rightmost digit (which is the check digit) and moving left, double the value of every second digit.
If the result of this doubling operation is greater than 9, then sum the digits of the result (e.g., 16: 1 + 6 = 7, or subtract 9, which is equivalent).
Take the sum of all the digits (both doubled and undoubled).
If the total modulo 10 is equal to 0, then the number is valid according to the Luhn formula.