Once you have opened your yogurt it will last for about 7 days in the refrigerator. You can choose to freeze your open yogurt and then will gain a few more weeks, lasting you a month. Of course, this is only true if you have stored it properly in the fridge and it hasn't been left out on the counter for any length of time. Also, make sure that you are also going to the "use by" date on the container as well.