How to use
- Enter the card number with or without spaces or hyphens; never enter the PIN, CVV or a one-time code.
- Check whether the length and Luhn checksum are valid.
- If the checksum is wrong, compare the expected final check digit with the number you typed.
Options explained
- Length
- Payment card numbers usually contain 12–19 digits. Length alone does not identify a bank or prove that a number was issued.
- Luhn checksum
- Starting from the right, alternating digits are doubled and reduced, then all digits are summed. A valid total is divisible by 10.
- Check digit
- The final digit is chosen so the whole number passes Luhn. The calculator can show which final digit would make the typed prefix valid.
Safe test numbers
4111 1111 1111 1111 and 5555 5555 5555 4444 are widely published test numbers that pass Luhn but are not usable payment accounts.
The Luhn algorithm detects every single-digit error and most adjacent digit transpositions. It is an error check, not encryption, authorization or fraud detection.
Frequently asked questions
Does a valid result mean the card is real?
No. Luhn only checks the number's internal arithmetic. It cannot tell whether the account was issued, is active or has funds.
Is my card number uploaded?
No. Validation runs locally in your browser. Even so, use a published test number when you only need to test the algorithm.
Do all payment cards use Luhn?
Most major credit and debit card schemes do, but a number can have a different format or use another check system.
Privacy
This tool runs entirely in your browser. Your files and text are processed on your device and are never uploaded to our servers.