Credit Card Validator Guide: What the Luhn Check Can and Cannot Tell You
Understand how the Luhn checksum works and why passing it says nothing about a real account.
What is the Credit Card Validator?
Type a card number and this tool runs the Luhn checksum and identifies the likely brand from its starting digits, covering Visa, Mastercard, American Express and Discover. This is a format check only: it never shows whether a card is real, active, or belongs to anyone, and nothing you type is stored or sent anywhere. Never enter a real card number into a page you do not trust.
How to use it
- Type the card number; spaces and dashes are ignored.
- Click Validate.
- Read the Luhn result and the detected brand, remembering it is format only.
Worked example
For the sample 4242424242424242, the tool reports Format valid (Luhn): Yes, Brand: Visa and 16 digits, with a note that this is a format check only and does not show whether a card is real or active.
How does the Luhn check work?
Working from the right, every second digit is doubled, digits over nine have nine subtracted, and the total must be a multiple of ten. It catches most single-digit typos, but it cannot verify an account.
Frequently asked questions
Does a passing Luhn check mean the card is real?
No. Luhn only checks that the digits fit the checksum pattern, which any well-formed test number also does.
Is my card number stored?
No. The check runs in your browser and nothing is uploaded or kept.