Despite being one of the most overweight countries on Earth, the United States is one of the biggest waster of foods on the planet as well. And part of that is because we're too confused to understand expiration dates.
A survey conducted by researchers at Johns Hopkins revealed that many Americans throw out food before it's needed. The survey found that 84 percent of Americans say they occasionally throw out food on or near the date that's labeled as “best if used by” or “sell by." 37 percent of Americans say they throw out those foods near or on those dates regularly.
Obviously this is a misunderstanding of expiration date versus sell by date. An expiration date for milk or another product means it could actually be unhealthy to drink. But a sell by date simply means the product will begin losing its freshness after that date, but doesn't necessarily become unsafe to eat. As a result, the U.S. Department of Agriculture estimates that up to 31 percent of consumable food ends up being wasted by stores or consumers.
Part of the issue is expiration labeling is not federally regulated. So in some places, "use by" might literally mean, "Don't use after this date or it will become unsafe," while in other places "use by" will just mean, "Will start losing freshness after this date, but is still fine to eat."
Generally speaking, if you're looking at the date on a dry or non-perishable food, you will be fine even if it's a few days after the date. But if it's a perishable food, then you should take more caution.
Or you could just use your eyes and nose to see if anything's off.
(h/t Mental Floss)