About Two Weeks
The general consensus between the North Dakota University, whatscookingamerican.com, and Virginia State University, is that after opening a container of yogurt it will stay good for about two weeks as long as it's kept in the refrigerator. They do not recommend eating it after seven to 10 days.
Watch Expiration Dates
According to the Chobani Yogurt website, and the Dannon Yogurt website, yogurt can be eaten past the sell by or the expiration date on the containers as long as you don't see any mold growing on it or smell sourness that often comes with spoiled dairy products.
The Chobani Yogurt website says, "if the yogurt looks, smells, and tastes good, and there are no visible signs of mold, it's most likely okay to eat." If the yogurt passes the smell and the mold test it should be good to eat.