The length of time yoghurt is safe to eat after its expiration date depends on whether the date is a "sell by" or "use by" date. Regardless of the date, do not eat yoghurt that has a blue-green tint or smells or tastes unusually sour.
"Sell By" Date
Most yoghurt is stamped with a "sell by" date rather than an expiration date. The yoghurt should be good for about two weeks after the "sell by" date, according to Julie Garden-Robinson, a food and nutrition specialist at North Dakota State University.
"Use By" Date
A traditional expiration date is a date that follows a statement to "use by" that date. Do not eat yoghurt past the "use by" date because it could be unsafe to eat.
After a container of yoghurt has been opened, it should be tightly covered and eaten within 10 days. If the "use by" date or two weeks after the "sell by" date occurs sooner, then the yoghurt is only good until that date.