Credit Card Number Validator Online — Luhn Check and Card Type Detection

What Is Credit Card Number Validation?

Credit card numbers are not random — they follow a mathematical structure defined by the Luhn algorithm (also called the Luhn formula or modulus-10 algorithm). The last digit of every credit card number is a checksum that makes the entire number pass the Luhn check. Additionally, each card network uses specific number prefixes (IINs/BINs) and fixed lengths.

Luhn validation catches typos immediately, before making an expensive network call to a payment processor. However, passing Luhn validation doesn't mean a card is active, has funds, or belongs to the person entering it — that requires authorization from the card network.

How to Validate a Credit Card Number

1. Remove spaces and dashes — normalize the input to digits only.
2. Detect card type — check the prefix against known IIN ranges.
3. Validate length — each card type has specific valid lengths.
4. Run Luhn algorithm — verify the checksum.
5. Validate CVV length — 3 digits for Visa/Mastercard/Discover, 4 for Amex.

Card Type Detection Rules

• Visa — starts with 4, length 13 or 16 digits.
• Mastercard — starts with 51–55 or 2221–2720, 16 digits.
• American Express — starts with 34 or 37, 15 digits.
• Discover — starts with 6011, 622126–622925, 644–649, or 65, 16 digits.
• Diners Club — starts with 300–305, 36, or 38, 14 digits.
• JCB — starts with 3528–3589, 16 digits.

Use Cases

Payment Form Development

During checkout form development, validate card numbers client-side to give immediate feedback before submission. Display the card type logo as the user types (Visa/MC/Amex icon updates based on the prefix). This improves UX significantly.

Testing Payment Integrations

Payment processors like Stripe, Braintree, and Adyen provide test card numbers. A validator helps you understand why specific test numbers work — they pass Luhn and match the expected card type — and generate valid-looking test numbers for different card types.

Frequently Asked Questions

What is the Luhn algorithm?

The Luhn algorithm is a simple checksum formula: starting from the rightmost digit and moving left, double every second digit. If doubling produces a number greater than 9, subtract 9. Sum all digits. If the total is divisible by 10, the number is valid. It was designed to detect accidental errors, not malicious fraud.

Does passing Luhn validation mean a card is real?

No. Luhn validation only confirms the number is mathematically well-formed. A number can pass Luhn but still be completely fictional, expired, declined, or fraudulent. Real card authorization requires connecting to the card network through a payment processor.

What are Stripe's test card numbers?

Stripe provides several test cards: 4242 4242 4242 4242 (Visa, always succeeds), 4000 0000 0000 0002 (always declined), 4000 0027 6000 3184 (requires 3D Secure). All pass Luhn validation and use any future expiry date and any 3-digit CVV.

Is it safe to validate credit card numbers in the browser?

Luhn validation (checking the number format) is safe client-side because it uses no real card data. However, never transmit raw card numbers to your own servers — use Stripe.js, Braintree Drop-in UI, or other PCI-compliant JavaScript SDKs that tokenize the card number before it leaves the browser.

What is a BIN number?

BIN (Bank Identification Number) or IIN (Issuer Identification Number) is the first 6–8 digits of a card number. It identifies the card network (Visa, Mastercard), the issuing bank, and the card's country of issue. BIN lookup can be used for risk assessment and routing logic.