Credit Card Validator

Credit card validator: Luhn check and network detection

This credit card validator tells you in real time whether a card number is well-formed: it runs the Luhn algorithm (the mod-10 checksum every major card network uses), identifies the network from the first digits — Visa, Mastercard (including the newer 2-series), American Express, Discover, RuPay, Diners Club, JCB, UnionPay, Maestro and Mir — and checks that the length is right for that network. The number is formatted as you type, Amex-style 4-6-5 included.

It is built for developers testing checkout forms, support staff checking a number read over the phone, and anyone who wants to understand why a payment form says “invalid card number”. Everything runs in your browser: the number is never transmitted or saved, and the tool never asks for a CVV, expiry date or cardholder name — details no validator needs.

How to use the Credit Card Validator

1. Type or paste the card number. Spaces and dashes are fine; the field groups the digits automatically.
2. Read the verdict: “Valid format” when the Luhn check, network prefix and length all agree, or a specific reason when they do not.
3. Check the breakdown for the network, region, IIN/BIN, length rules and the masked form, and scroll to the Luhn table to see the arithmetic.
4. For testing a payment form, choose a network and press “Use a well-known test number” or “Generate a random Luhn-valid number”.

Credit Card Validator features

How the Luhn algorithm works, step by step

Example with 4539 1488 0343 6467: doubling every second digit from the right (4→8, 3→6, 1→2, 8→16→7, and so on) and subtracting 9 where needed turns the digits into 8 5 6 9 2 4 7 8 0 3 8 3 3 4 3 7, which sum to 80, which is divisible by 10, so the number is valid. Change one digit and the sum lands on a non-multiple of 10. The check catches every single-digit typo and almost every swap of two adjacent digits (only 09↔90 slips through).

Luhn is a typo detector, not a security feature: it is public and easy to satisfy, which is exactly why test numbers are easy to make.

1. Starting from the right-most digit (the check digit) and moving left, double every second digit.
2. If doubling gives a number above 9, subtract 9 (equivalently, add the two digits together).
3. Add up all the digits — the doubled ones and the untouched ones.
4. If the total is a multiple of 10, the number passes.

Card number structure and network prefixes

A card number (PAN) has three parts: the issuer identification number (IIN or BIN, the first 6 — now 8 — digits, which identify the network and the bank), the account identifier, and the final Luhn check digit. The first digit is the major industry identifier: 3 for travel and entertainment (Amex, Diners, JCB), 4 and 5 for banking (Visa, Mastercard), 6 for merchandising and banking (Discover, RuPay, UnionPay, Maestro).

What “valid” does and does not mean

• A valid format means the number could exist. Only the issuing bank can confirm that the card is real, active, not reported stolen and has credit available — that happens during an authorisation, never in a validator.
• The test numbers here (such as 4111 1111 1111 1111 or 5555 5555 5555 4444) are published by payment processors for sandbox use. They pass Luhn but cannot be charged; using them on a live checkout simply fails.
• Never paste a real card number into a site you do not trust, and never share the CVV — it is the one part designed not to be stored anywhere.
• For bank account numbers rather than cards, use the IBAN Validator; for form input checks on addresses, try the Email Validator.