Card Number Validator

How Card Number Validation Works

Every credit and debit card number includes a check digit — the last digit — calculated using the Luhn algorithm (ISO/IEC 7812-1). The algorithm doubles every second digit from the right, sums the result, and checks whether the total is divisible by 10. This catches the most common transcription errors: single-digit typos, adjacent transpositions, and dropped or added digits. Luhn validation does not confirm that an account exists or has funds — it only confirms that the number is structurally well-formed.

Card Network Prefix Ranges

Card networks are identified by the first few digits of the number, called the Issuer Identification Number (IIN). Visa starts with 4. Mastercard uses 51–55 and the newer 2221–2720 range. Amex uses 34 or 37 with a 15-digit format and unique 4-6-5 digit grouping. Discover uses 6011, 65, and 644–649. JCB covers 3528–3589. Diners Club uses 300–305, 36, and 38 with 14 digits. UnionPay starts with 62. These prefix rules are published by the card networks and are stable across years — they change far less often than the BIN tables that map individual ranges to issuing banks.

Validation in Payment Integrations

Client-side Luhn validation belongs in every payment form — it catches obvious typos before the number hits your payment processor, saving a round trip and reducing declined-transaction noise. Combined with network detection, it also lets you show the right card logo instantly and enforce network-specific formatting. I build payment integrations, PCI-compliant data pipelines, and custom checkout flows that handle validation, tokenization, and processor routing. See custom application development, explore integration services, or get in touch.