Luhn Algorithm Calculator – Credit Card & ID Number Validator

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Validate identification numbers using the Luhn algorithm (mod 10). Commonly used for credit cards, IMEI, and social insurance numbers.

Number: 4485275742308327
Luhn Check: ✅ Valid
Card Type: Visa
Check Digit: 7
Step-by-step:
Digits: 4 4 8 5 2 7 5 7 4 2 3 0 8 3 2 7
Doubled: 8 8 16 5 4 7 10 7 8 2 6 0 16 3 4 7
Sum: 8+8+7+5+4+7+1+7+8+2+6+0+7+3+4+7 = 84
84 ÷ 10 = 8 remainder 4 ❌

Note: The Luhn algorithm detects most single-digit errors and adjacent digit transpositions. It is not a cryptographic check and does not confirm that a card was actually issued.

What is the Luhn Algorithm?

The Luhn algorithm (also known as the "mod 10" or "modulus 10" algorithm) is a simple checksum formula used to validate various identification numbers, such as credit card numbers, IMEI numbers, and Social Security numbers [citation:1][citation:5].

The algorithm was developed in 1954 by Hans Peter Luhn, an IBM researcher, and is now in the public domain [citation:2][citation:6]. It is widely used by major payment systems including Visa, Mastercard, American Express, and Discover [citation:6].

How it works:

  1. Starting from the rightmost digit, double every second digit.
  2. If doubling results in a two-digit number, sum those digits (or subtract 9).
  3. Sum all digits (doubled and non-doubled).
  4. If the total is divisible by 10, the number passes the Luhn check [citation:6].

Key characteristics:

  • Detects — most single-digit errors and adjacent digit transpositions
  • Does not detect — transposition of 09 to 90, and some double errors [citation:7][citation:8]
  • Not cryptographic — it's a checksum, not an encryption method [citation:5][citation:6]

The algorithm is widely applied to bank card numbers, IMEI codes, SIM card ICCIDs, and Canadian Social Insurance Numbers [citation:1][citation:4][citation:5].

How to Use This Calculator

  1. Enter a number: Type or paste the number you want to validate (e.g., a credit card number or IMEI). Spaces and dashes are automatically removed.
  2. Validate: Click “Validate” or press Enter to check if the number passes the Luhn algorithm.
  3. Generate Check Digit: Click “Generate Check Digit” to calculate the correct check digit for the entered prefix.
  4. Interpretation: The result shows whether the number is valid, identifies the card type (if applicable), and displays the step-by-step calculation.

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