Credit Card Number Validator

1. Enter a credit card number in the input field (spaces and dashes are ignored).
2. Click "Validate" or press Enter.
3. See the detected card type (Visa, Mastercard, Amex, Discover) and whether the number passes Luhn validation.
4. Try the example test card numbers to see the tool in action.

What is the Luhn Algorithm?

The Luhn algorithm (also known as the modulus 10 algorithm) is a simple checksum formula used to validate identification numbers such as credit card numbers, IMEI numbers, and Canadian Social Insurance Numbers. Created by IBM scientist Hans Peter Luhn in 1954, it was designed to protect against accidental transcription errors, not deliberate fraud. The algorithm detects any single-digit error (typing a 3 instead of a 5) and most transpositions of adjacent digits (swapping 34 to 43). Credit card companies use this as a first-pass check before sending a number to the payment network for authorization.

How the Luhn Check Works

Starting from the rightmost digit and moving left, the algorithm doubles every second digit. If doubling produces a value greater than 9, it subtracts 9 from the result. It then sums all the digits (both the doubled and unchanged ones). If the total is evenly divisible by 10, the number passes the Luhn check. For example, with the number 4539578763621486: after doubling alternate digits and adjusting values over 9, the sum equals 70, which is divisible by 10, so the number is valid. This tool also identifies the card network by examining the leading digits (called the BIN or IIN range).

Common Use Cases

• Testing payment integration during e-commerce development
• Validating card number format before submitting to a payment gateway
• Identifying card type (Visa, Mastercard, Amex, Discover) from the number
• Detecting data entry errors in customer support workflows
• Verifying test card numbers in staging and QA environments
• Educational purposes for understanding checksum algorithms

Card Network Identification

Each card network uses specific number prefixes and lengths. Visa cards start with 4 and are 13 or 16 digits long. Mastercard numbers begin with 51 through 55 (or the newer 2221-2720 range) and are 16 digits. American Express cards start with 34 or 37 and are 15 digits. Discover cards begin with 6011, 644-649, or 65 and are 16 digits. These prefix ranges are called Bank Identification Numbers (BINs) or Issuer Identification Numbers (IINs). Knowing the card type is useful for displaying the correct logo in checkout forms and applying network-specific validation rules. Well-known test numbers like 4111111111111111 (Visa) and 5500000000000004 (Mastercard) pass Luhn validation but are not connected to real accounts.

For validating other data formats, try the JSON Validator. For testing regex patterns used in form validation, use the Regex Tester. For number system conversions, see the Number Base Converter.