Plus, a way to know where they came from and how they've been graded.
Credit: Adobe: draganagordic

Many of us are familiar with barcodes and UPC codes on products that we buy in the supermarket. Eggs are a little bit different, however. Nearly all cartons are marked with a set of numbers that you're probably not familiar with.

Eggs sold commercially in the United States are marked with a few codes that you usually find next to the carton's "best by" date, or expiration date. And most shoppers use the expiration date to determine how fresh eggs are. How many times have you hunted for a carton in the back of the row with a better expiration date, right?

But there's actually another label that can tell you the exact date of when your eggs were packed and shipped off to retailers.

It's a three-digit code that's usually adjacent or right underneath the expiration date, and it refers to the date by its number in a calendar year. For example, since there are 365 days in most years (except for leap years) January 1 would be number 001, February 1 would be 32 (since it's the 32nd day) and December 31 be number 365. Here's a handy chart to help convert your code to a date if you need some help.

We know that eggs can easily spread foodborne illness beyond their expiration dates, which is why a pack date might be a better indicator of whether they're safe to eat or not. Eggs are safe when they're stored in a refrigerator for up to five weeks after they were packed, according to the United States Department of Agriculture.

The national agency also provides an egg-stamp pocket guide to download and use if you're looking to convert the Julian calendar code located on your egg carton to an actual date this year.

Credit: Guide courtesy of the USDA.

Learn more about foodborne illnesses and how to protect your family:

If you're noticing a few other codes on your box, don't be confused—these numbers convey the processing plant that the eggs were packed in, as well as an official grade indicating the determined quality of the egg itself. The plant code starts with the letter "P" followed by a four-digit number: the USDA also keeps a running list of all plants, so you can see where these eggs were first harvested if you're interested in doing so.

You're most likely to immediately recognize the last code on your box, which is the USDA's official grade. These range between AA and B, and the better grades (AA and A) are the freshest and highest quality available. Grade B eggs aren't dangerous for your health, but they won't taste as great as other options—you'd probably use these eggs for baking or for other recipes where eggs aren't the main attraction.

Given that eggs often are recalled for salmonella contaminations in the past, understanding which region they came from and when they were packed can be an essential step to keeping your family safe.