Category: Developer tools
Luhn Checksum Validator
Validate numbers with the Luhn algorithm and calculate check digits
Validate credit card numbers and other identifiers against the Luhn (mod 10) checksum, or calculate the check digit needed to complete a partial number. Runs entirely in your browser.
Everything on this page is processed in your browser. Nothing is uploaded.
What this tool does
The Luhn algorithm, also known as the mod 10 algorithm, is a simple checksum formula used to validate a range of identification numbers, including credit and debit card numbers, IMEI numbers and some government IDs. It works by doubling every second digit from the rightmost digit, subtracting 9 from any result over 9, and checking that the total sum is a multiple of 10. This tool runs the same check locally, and can also calculate the check digit that would make a partial number pass.
How to use it
- Choose Validate to check a full number, or Compute check digit for a number missing its final digit.
- Enter the number, digits only or with spaces and dashes.
- Read the result: valid or invalid, or the calculated check digit.
Privacy
This tool runs entirely in your browser. Your input is never uploaded, stored or shared — closing the tab removes it.
Frequently asked questions
- Does this tool identify the card network or issuer?
- No. It only checks the Luhn checksum, which confirms the number is well-formed. It cannot tell you whether a card is real, active, or which bank issued it.
- Is my number sent anywhere?
- No. The Luhn calculation runs entirely in your browser; nothing you type is uploaded or stored.
- What else uses the Luhn algorithm besides card numbers?
- IMEI numbers for mobile devices, Canadian Social Insurance Numbers, and several national ID schemes also use a Luhn check digit.