This article originally appeared on What’s Good by Vitamin Shoppe.

If you stand in the middle of the grocery store confused about the difference between the expiration, ‘use by’, and ‘best by’ dates on foods, you’re not alone! Clients ask me all the time what the dates printed on foods really mean—and how much they really matter.

Before we get into it, you may be surprised to know that those confusing dates aren’t actually required to be there in the first place. While the FDA (Food and Drug Administration) regulates the safety of packaged foods and drugs and the USDA (United States Department of Agriculture) regulates fresh produce and meats, the states decide whether or not food items must be dated somehow—and just more than half of them require it. In fact, in many parts of the U.S., the food supply isn’t dated at all. (The one exception to this: baby formula, which must display a use-by or expiration date to ensure each nutrient listed is at peak value when it’s sold.)

If there are dates on the packaged foods you pick up at the grocery store, though, here’s what they actually mean.

‘Sell By’ Dates

You typically find ‘sell by’ or ‘pull by’ dates printed on dairy and meat products. These indicate the last date a food should be sold, and help you understand how fresh it is. If stored properly, these foods should still be safe to consume a few days beyond their ‘sell by’ dates date, but they should not be on store shelves past it. If you see a product on-shelf with a ‘sell by’ or ‘pull by’ date that’s come and gone, don’t buy it!

Egg cartons may also display ‘sell by’ dates, but eggs can stay fresh for up to three to five weeks after purchase if you store them in the coldest part of your fridge.

‘Best If Used By’ Dates  

‘Best if used by’ or ‘best if used before’ highlight when a food is at its highest quality. Though still safe to eat after this date, the food may lose some of its freshness, flavor, and nutritional value.

Cans often display ‘best if used by’ dates. You’ll notice that high-acid foods—like canned tomatoes, grapefruit, and pineapple—are best used within 12 to 18 months, while more stable, lower-acid foods—like canned meat, poultry, fish, and vegetables—can last for up to two to five years if stored in a cool, dry place.

Pack Dates

Used for foods that have a longer shelf life—like anything canned or frozen—a pack date is the date a food was manufactured, processed, and packaged. It’s either written as ‘packed on,’ followed by the date in ‘month/day/year’ form or as a three-digit number (with ‘001’ being January 1 and ‘365’ being December 31).

If a food doesn’t have a ‘best by’ date, the pack date can help you figure out when it’s at its best. Most unopened canned goods can last a year from this date before starting to lose flavor and nutrient quality, while frozen foods lose some flavor and nutrition after a few months.

Another place you may find ‘pack’ dates: eggs.

Expiration Dates

An expiration or ‘use by’ date indicates the last date a food should be eaten, according to its manufacturer.

Unless you freeze meat, poultry, or fish upon purchase, abide by their expiration dates. Properly refrigerated milk can keep for a few days beyond this date, but carefully observe and smell it before pouring a glass. Meanwhile, unopened yogurt can last a few weeks past its expiration date, but should be used within a few days once opened.

Closed Dates

Closed or ‘coded’ dates are used by the manufacturer to identify and locate their products. You’ll see these as a series of letters and numbers somewhere (often on the bottom) on shelf-stable cans and boxes. The jumble refers to when and where the food was manufactured. It often starts with three numbers to indicate the day packaged, followed by another number to indicate the year.

These coded dates are more for the food manufacturers than for consumers—unless, of course, in the event of a recall. When manufacturers need to recall certain foods, they often release these coded dates so consumers can identify whether their particular product may be tainted.

The Bottom Line

“For the vast majority of products out there, shelf life is based purely on quality—not safety,” says Scott Hood, director of Global Food Safety at General Mills. “If you’re Spring cleaning, it is highly likely that the dry and canned products in your pantry are safe beyond whatever date is printed on them.” Same goes for the foods in your freezer (though temperature fluctuations can negatively impact quality).

While you do need to be more careful with the foods in your fridge, your gut instinct usually means more than whatever dates are printed on them. If stored properly, a product should last beyond whatever date is listed; just pay attention to how the food looks, smells, and tastes. My mantra is “when in doubt, throw it out.” If it looks, smells, or tastes funky, ditch it.

If you have any other questions about food storage and safety, check out foodsafety.gov, a resource created by the USDA, FDA, and CDC. And know this: Changes to food packaging are coming! Recently-proposed legislation aims to clear up the confusion about the dates printed on foods and standardize the wording used.