What does the Luhn algorithm check?

It transforms alternating digits from the right, adds them, and checks whether the total is divisible by 10. It catches common single-digit and adjacent-transposition mistakes, but it is not an issuer lookup or proof that a number is real.

Can I generate a Luhn check digit?

Yes. Enter the number without its final check digit. The page appends the digit that makes the complete total divisible by 10 and lets you copy it.

Are spaces and hyphens allowed?

They are presentation marks and are ignored. Other characters are refused so a typo cannot be silently treated as a different number.

Does the checker contact a payment network?

No. It applies the checksum locally to the digits you enter and does not verify whether an account exists.

Luhn Algorithm Checker

Paste a digit string to run the Luhn checksum in your browser. The page says whether its total is divisible by ten, shows the checksum working, and can append the correct next check digit to a partial number. Spaces and hyphens are ignored, so 7992-7398 713 is checked the same way as 79927398713. A Luhn result detects transcription errors; it does not prove that an account, card or identifier was issued or active, and the value never leaves this device.

Luhn check for 79927398713Validchecksum divisible by 10

Number

Checksum
70; divisible by 10
Next check digit
799273987138
Working
Double every second digit from the right, subtract 9 when the double is over 9, then add the digits: 70. A valid number has a total divisible by 10.
Accuracy
The Luhn check is exact for the digits entered. It detects many transcription errors, but it does not prove that a number was issued, belongs to anyone, or is safe to use.

Common questions

What does the Luhn algorithm check?: It transforms alternating digits from the right, adds them, and checks whether the total is divisible by 10. It catches common single-digit and adjacent-transposition mistakes, but it is not an issuer lookup or proof that a number is real.
Can I generate a Luhn check digit?: Yes. Enter the number without its final check digit. The page appends the digit that makes the complete total divisible by 10 and lets you copy it.
Are spaces and hyphens allowed?: They are presentation marks and are ignored. Other characters are refused so a typo cannot be silently treated as a different number.
Does the checker contact a payment network?: No. It applies the checksum locally to the digits you enter and does not verify whether an account exists.

The Luhn check is exact for the digits entered. It detects many transcription errors, but it does not prove that a number was issued, belongs to anyone, or is safe to use.