Luhn Checker & Check Digit Calculator
Validate a card, IMEI or account number with the Luhn checksum and compute its check digit — runs 100% in your browser, no upload.
✓ Valid — passes the Luhn checksum
Card network: Visa
79927398713🔒 The checksum is computed in your browser — nothing is uploaded or stored.
What is the Luhn algorithm?
The Luhn algorithm (also called the mod 10 checksum) is a simple formula used to catch accidental typos in identifier numbers such as credit card numbers, IMEI device serials and some national ID numbers. Starting from the rightmost digit, you double every second digit, subtract 9 from any result over 9, add everything up, and check whether the total is divisible by 10. If it is, the number passes the checksum.
Validating and generating check digits
Paste a full number to see instantly whether it is valid. Spaces and dashes are ignored, so formats like 4242 4242 4242 4242 work fine. To build a valid number, enter the digits without the final check digit and this tool computes the single digit you should append. For a full number it also identifies the card network — Visa, Mastercard, American Express, Discover and others — from the opening digits, so a card-shaped number that fails the checksum reads as a likely typo. Remember: passing the Luhn check only means the number is well-formed, not that the card or account actually exists or is active.
Frequently asked questions
Is my card number uploaded or stored anywhere?
No. The checksum is calculated entirely in your browser using JavaScript. Nothing you type is sent to a server, logged or stored.
Does a valid Luhn checksum mean the card is real?
No. The Luhn check only verifies that the digits are internally consistent, which catches most typos. It cannot tell you whether a card exists, is active, or has funds.
What is a check digit?
The check digit is the final digit of many identifier numbers. It is derived from the other digits so that the whole number satisfies the Luhn formula, giving a quick way to detect single-digit errors.