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Luhn Checker

Luhn Checker is part of Toolspire and is ready as soon as this page loads. Spaces are ignored. This checks a digit pattern used on many card and account numbers. It does not say an account exists, and it does not generate numbers.

Runs in this tabFreeNo account

On this page

What you can do here

The published sample

79927398713 is the worked example people use to test a Luhn implementation.

Spaces ignored

Groups of four can be pasted.

No generator

The page will not invent a number that passes.

The sequence

How to use the Luhn Checker

  1. 1

    Paste the sample

    It should read Valid.

  2. 2

    Change the last digit

    It should read Invalid.

  3. 3

    Do not treat valid as authorised

    The arithmetic is public. Issuers keep the account list.

Worth knowing

  • Luhn Checker on Toolspire: 79927398713 passes the Luhn check. The weighted sum divides by 10.
  • From the right, every second digit is doubled, and a double above 9 has 9 subtracted.
  • The sample’s check digit is the final 3.
  • A passed check does not mean a bank account or a card is real.

A mod-10 digit check

Luhn walks the digits from the right, doubles every second one, subtracts 9 when a double is at least 10, and asks whether the sum ends in 0. 79927398713 does. The test catches a single wrong digit or a swap of two adjacent digits in many cases. It does not contact a bank, and this page will not produce a new number that satisfies it.

FAQ

Questions about Luhn Checker

Where does Luhn Checker run?

Luhn Checker runs in this tab on Toolspire. What you type or drop in is not sent to us and is not stored on a server.

Does 79927398713 pass?

Yes.

What does doubling do to 8?

16, then subtract 9, leaving 7. That is the same as adding the digits 1 and 6.

If the check passes, is the card real?

No. Only the digits are consistent with Luhn.

Will this make a valid number for me?

No.

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