🔍 Credit Card Checker

⚠️ Note: This educational tool simulates how the Luhn algorithm works. It does not verify real credit cards and has no connection to any financial institution.

Test a credit card number to see if it could be valid. Use your own or generate an example below.

Enter a card number:

🔎 Curious how it works?

The Luhn algorithm is a simple and widely-used method to verify identification numbers like credit cards.

When a credit card number is entered, systems use the Luhn algorithm to check whether the number structure is mathematically plausible. It helps detect mistyped or invalid numbers before a transaction even starts.

The process includes the following steps:

Start from the rightmost digit and move left, reversing the number internally.
Double every second digit (counting from the right).
If a doubled value is greater than 9, subtract 9.
Sum all the digits. If the total is divisible by 10, the number is likely valid.

Also, the first digit often hints at the card issuer:

3 → Amex (American Express)
4 → Visa
5 → Mastercard
6 → Discover

🔢 Step-by-Step Luhn Breakdown

The Luhn algorithm processes the number from right to left. Here's how it works step by step:

Step 1: Reverse the number

Credit card number:
Reversed credit card number:

Step 2: Performing the corresponding calculation

Reversed digit	Action	Result

Step 3: Sum all digits

Step 4: Check validity

If the total sum is divisible by 10, the number is valid. Otherwise, it's invalid.