A Luhn algorithm test runs the mod-10 checksum that catches most typos in card, IMEI and account numbers before they ever reach a payment gateway. Paste a number and the tool doubles every second digit from the right, sums the digits, and tells you whether the total divides evenly by ten. It is the same check most checkout forms run in the browser, packaged so you can run it on demand as often as you like.
Key Features
- Instant mod-10 pass or fail from a single click, with no account or install required
- Cleans spaces, dashes and dots before calculating, so pasted numbers work as-is
- Digit-by-digit breakdown shows exactly which position threw the total off
- Reports length and checksum separately, so a well-formed number with one bad digit stands out
- Works on any numeric string: card numbers, IMEI, NPI, SIN and account references
- Bulk mode lets you paste a column of numbers and read pass or fail line by line
- Runs locally in your browser, so pasted values are never stored or transmitted
The tool implements the standard Luhn formula as published in ISO/IEC 7812. Starting at the rightmost digit and moving left, every second digit is doubled, and any result above nine has nine subtracted before the sum is taken. The final total must be a multiple of ten for the number to pass. Input is capped at 19 digits, which covers the longest card numbers in circulation, and non-numeric characters are stripped automatically so pasted values never need reformatting first.
Delivery is instant: the tool unlocks in your browser as soon as checkout completes, and a backup access email follows within a few minutes. There is nothing to ship and nothing to install. If it will not load or a checksum result looks wrong, contact us within 30 days for a replacement or a full refund.
What does a Luhn test actually prove?
Only that the digits are internally consistent, meaning a single mistyped or transposed digit is unlikely. It says nothing about whether a number is in use, funded or authorized.
Does passing the check mean a card number is valid?
No. Luhn is a format check, not a validity check. Only the issuing bank can confirm that an account exists and will approve a charge.
Which numbers can I run through it?
Any string of digits: payment card numbers, IMEI handset IDs, National Provider Identifiers, Canadian SINs and most account references that use the same mod-10 scheme.