Check Digit: Credit Cards with 16 digits Please insert the first 15 digits of the 16-digit number to get the check digit (16th digit). Or you can enter 16 digits, and the last digit will be compared with the calculated check digit for the first 15 digits. Enter the number here: Click on to submit the number.Click on to clear the field. Check Digit: Credit Cards with 13 digits Please insert the first 12 digits of the 13-digit number to get the check digit (13th digit). Or you can enter 13 digits, and the last digit will be compared with the calculated check digit for the first 12 digits. Enter the number here: Click on to submit the number.Click on to clear the field.