A luhn check test tells you whether a string of digits satisfies the Luhn algorithm — the mod-10 checksum that catches mistyped numbers before they cause trouble. Enter any card-length number, IMEI, or identification number and the tool returns a clear pass or fail, along with the arithmetic behind the result. It takes a second and requires nothing more than the digits themselves.

What does a luhn check test actually do?

It reads the number from right to left, doubles every second digit, adds the digits of each result together, and checks whether the grand total is divisible by ten. If it is, the number passes; if it isn't, at least one digit is wrong, missing, or out of order.

Key Features

• Instant pass or fail result for any digit string you paste in
• Handles 12- to 19-digit payment card numbers, IMEIs, and other check-digit identifiers
• Displays the doubling step, the digit sums, and the final total so the math is easy to follow
• Ignores spaces, dashes, and other formatting characters automatically
• Runs entirely in your browser, so nothing you enter is stored or transmitted
• One-click copy for the cleaned-up, digit-only version of the number
• No account, no signup, and no software to install
• Accepts long lists, one number per line

How the check digit math works

The rightmost digit is the check digit. Starting with the digit immediately to its left, every second digit is doubled; when a doubled value lands above nine, subtract nine (adding the two digits of the result gives the same answer). Every value is then summed, and a valid number produces a total ending in zero. Because the algorithm looks only at digit positions and values, it is fully deterministic — the same input always yields the same answer, and a single transposition of two adjacent digits will almost always fail.

Delivery and refunds

This is a browser-based tool, so there is nothing to ship and nothing to wait for: access is immediate once your order is placed. If it does not do what you need, contact support within 30 days for a full refund — no return label and no questions about why it was not a fit.

Does a passing luhn check mean the number is real?

No. Luhn only shows that the digits are internally consistent. It says nothing about whether an account exists, is active, or belongs to anyone. It is an error-detection formula, not a verification or lookup service.

Can I test several numbers at once?

Yes. Paste one number per line and the tool reports a separate result for each, which is useful when you are cleaning up a spreadsheet of identifiers or catching typos in a batch.