Ever wonder if the unopened yogurt in the back of your refrigerator is still good to eat—even if it’s a week past the date stamped on the package? Maybe you open it and take a sniff, or turn it this way and that under a bright light to see if it looks OK. Well, while nose and eye tests are iffy at best, there are basic food rules you can use as a guide:

“Sell by”: Buy the product before the date expires. (Stores use this as a guide for when to pull a food off the shelf.)

“Best if used by (or before)”: For best flavor or quality, it is recommended that you eat or use the product by this date.

“Use by”: This is the last date the manufacturer recommends you eat the food to taste it at peak quality. But it is still edible.

What’s also important: Follow proper handling, preparation and storage procedures to avoid food cross-contamination and spoilage as well as foodborne illness. And let’s not toss this common sense advice: When in doubt, throw it out!