Credit card number validator

How it works

Validation walks the digit string from right to left, doubling every second digit and subtracting 9 from any result over 9, then checks whether the total sum is a multiple of 10 — the standard Luhn/mod-10 algorithm used by every major card network; network identification is a separate step done purely by matching the leading digits against each issuer's published prefix ranges (4 for Visa, 51-55 for Mastercard, 34/37 for Amex, and so on).

FAQ

Does a valid result mean the card is real or active?

No — Luhn is just a checksum that catches typos and transcription errors; it says nothing about whether the account exists, is open, or has funds, and plenty of fake numbers (including this page's placeholder) pass it on purpose since it's a public, well-known formula.

Why does it say Mastercard for a number starting with 2223?

Mastercard expanded its issuing range in 2017 to include 2221-2720 alongside the original 51-55 prefixes, so both ranges are checked — a card starting with 2223 is a legitimate (newer-range) Mastercard prefix, not a misdetection.