Confusion over those tiny expiration date stamps leads consumers to throw away approximately 133 billion (!) pounds of wasted food a year. Here's how to know when it's really time to toss that carton of milk.

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Food waste is a big problem: Americans estimate they toss $640 worth of food each year, according to a new survey from the American Chemical Council. And an earlier analysis by the Institute of Food Technologists (IFT) found that consumers to throw away approximately 133 billion (!) pounds total of wasted food a year.

Confusion over those tiny date stamps on food products is a big part of the problem.

That's because, while they may sound similar, “use-by,” “sell-by,” and “best-by” dates actually mean three different things when it comes to food safety. And none of these dates are literal expiration dates that reflect exactly when a product will become harmful or dangerous to eat. They only mark the point at which it's reached peak quality, consistency, or flavor—leading to a lot of confusion and still-good food thrown out before its time, according to the IFT.

To help you decide when it’s really time to toss that carton of milk, we've laid out the differences between common dates you'll find on food packaging.

Use-by date

You should, theoretically, eat food before this date, which is based more on when the quality of the product will go down than the chance that it will make you sick. But “quality is likely to go down much faster and safety could be lessened” after this point, Bob Brackett, PhD, director of the Institute for Food Safety and Health, noted in a press release. So when in doubt, it's a good rule of thumb to throw food out on or very close to this date.

Best-by date

Much like the "use-by date," this number tells consumers when a product should be eaten to guarantee ideal flavor and quality, not when a food will go bad.

Sell-by date

This marking informs retailers of the date by which they should sell the product or remove it from store shelves. Food is still safe for at-home consumption well after this point. In fact, according to Brackett, “typically one-third of a product’s shelf life remains after the 'sell-by' date for the consumer to use at home.”

Bottom line: While these dates are guidelines—and a good starting point—they're not going to help you determine when food will make you sick, or even when exactly you should throw it out. The good news is, most food takes longer than you'd think to go bad.

Always try to make sure your cold food stays cold and that your cooked food stays hot, since bacteria multiply the fastest between 40 degrees and 140 degrees. To keep them from growing, refrigerate food at less than 40 degrees, and reheat cooked leftovers to at least 165 degrees. And keep in mind the “2-2-4” rule of thumb: Don’t leave food out longer than 2 hours, refrigerate it in containers less than 2 inches deep, and use or freeze all refrigerated leftovers before 4 days.

For even more in-depth pointers on when you should really toss specific food items out, look to sites like The Food Keeper, a web sites with a searchable database of guidelines for storing and keeping everything from cereal to baby food safe, as well as