The average American has four credit cards in their wallet according to a report listed on MSN Money. If you multiply this amount by the number of American consumers, the number of credit cards in circulation is immense. Some of these credit cards may not be valid due to expiration, deactivation or fraud. For a merchant, it is important to ensure a credit card is valid when using it to process a transaction. For a consumer, it is essential to only carry credit cards that are valid for making purchases.

Step 1.

Review the card details. Check the expiration date printed on the credit card to insure the card is still valid. To check against fraud, you can compare the signature on the back of the credit card with another signature card like a driver’s license.

Step 2.

Compare the first digits on a credit card number to known standards per credit card issuer. For example, on a Discover credit card, ensure the first four digits of the credit card number are 6011. For a MasterCard, the first digits should be 51, for Visa the number should begin with a 4, for American Express the first numbers should be 34, and for Diner’s Club the card should begin with 300.

Step 3.

Ensure the numbers of digits in a credit card number are correct. Diner’s Club credit cards should have 14 digits, American Express cards should have 15 numbers, a Visa credit card should have 13 or 16 digits, a MasterCard should contain 16 digits and a Discover Card should have 16 numbers.

Step 4.

Perform a check digit calculation based on the Luhn algorithm. For a credit card that has an odd number of digits, multiply every other unit number by 2, starting with the second digit in the card number. For any total that is 9 or greater, subtract the number from 9. Add up the individual numbers in the card and the total should be divisible by 10 for the card number to be valid. The same calculation can be done for a card with an even number of digits. Instead of starting with the second digit for doubling, you start with the first digit on an even numbered card.

Step 5.

Try to process the card through a credit card terminal. Most invalid credit cards will not successfully process a transaction based on the electronic response received when attempting the transaction. You may need to contact your credit card processor to decode any error response you receive on the terminal.


If you doubt the validity of a card, contact your credit card processor or company for a real time check.


Fraudulent transactions can cost merchants money if they do not perform basic security checks like reviewing the signature validity.