MasterCard's unique first digit is 5, while Visa's is always 4. A Discover card's first digit is consistently the number 6. You can further identify credit cards that start with the same first ...

Your credit card number usually consists of 15 or 16 digits ... Visa starts with 4, a Mastercard is 5 and Discover is 6. Other numbers are used to identify the industry. For instance, 1 and ...