Luhn Number Validator
Verify any number with the Luhn checksum and find its check digit.
Generic Luhn (mod-10) check for any digit string. Spaces and dashes are ignored. Runs in your browser.
How to use
- 1 Paste or type a number (separators are ignored).
- 2 See whether it passes the Luhn checksum.
- 3 Treat the input as a number missing its check digit to get the digit that completes it.
- 4 Copy the completed number if you need it.
About Luhn Number Validator
The Luhn Number Validator applies the mod-10 checksum that guards identifiers across the world — credit card numbers, IMEI device serials, some national IDs and many account numbers.
Unlike a card-specific tool, this one is generic: paste any string of digits and it tells you whether the Luhn check passes, ignoring spaces and dashes so formatted numbers work as-is.
The Luhn algorithm doubles every second digit from the right, sums the results (subtracting nine from any two-digit product), and checks that the total is a multiple of ten.
It is designed to catch the most common human errors — a single mistyped digit, or two adjacent digits swapped — which is why so many systems append a Luhn check digit.
This tool also works the other way around.
Give it a number without its final check digit and it computes the single digit that makes the whole sequence valid, so you can complete an identifier or test your own implementation against a reference.
It is not a cryptographic safeguard — anyone can compute a passing number — only a defence against accidental typos.
Everything runs locally in your browser, so the numbers you test never leave the page.
FAQ
What is the Luhn algorithm used for?
It is a checksum that catches typos in identifiers such as credit cards, IMEI numbers and many account codes. It is not a security measure.
How is the check digit computed?
The tool finds the single digit (0–9) that, appended to your input, makes the whole sequence pass the Luhn checksum.