It should the original date of purchase but usually there's a conflict with the purchase date and the date AppleCare has on the computer. For example, you said you purchased the computer on the 1st of whichever month. On the computer, there's an estimated DOP. Again, usually it's the DOP but it can vary from the exact date or a week from DOP. It's not really a gain, just know that it will expire sometime near your original DOP.