Validate a number with the Luhn algorithm or calculate the check digit for a partial number.
Status
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Check digit
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Digits
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Enter the example value or paste your own input, choose the mode when one is available, and read the first result card for the direct answer. The output area gives a copyable block for code reviews, documentation, API tests, classwork or troubleshooting notes.
What the result means
The Luhn algorithm catches many typing errors in identification numbers that use a final check digit.
What is not included
Passing Luhn only proves the check digit is consistent. It does not prove that an account or card is real.
Privacy note
The calculation runs in your browser. Avoid pasting production secrets, credentials, private keys, customer data or regulated personal data unless your own policy allows browser-based tools.