Your credit card number is made up of 16 digits. The first one or two digits indicate whether it’s a Visa, Mastercard or American Express. Digits two to six indicate which financial institution issued the card, and the final 9 digits are your account number. The last digit is a “check” number used to verify the validity of your card number. The CVV number is the 3 or 4 digit security number on the back of the card.