People usually look for the "best before" date when doing their grocery shopping to determine the freshness of food. However, the date on a carton of eggs isn't always the best indicator of its freshness, as a Facebook viral post exposed.

"A few weeks ago I mentioned how the average grocery store egg might be 45 days old (or more) by the time you buy it. A few people asked for proof (beyond the LAW which states that a farmer has 30 days to carton and egg and then another 30 days to sell that egg after it's been cartoned)," Fresh Eggs Daily wrote on the social media site. "So today (1/19) I was shopping and snapped a few photos of some egg cartons. EVERY date I saw on them was between 352-355, meaning that those eggs were put in that carton on the 352nd-355th day of last year. Add to that the 19 days so far this year, and these eggs have all been in the carton for about a month (and could have been laid up to 30 days prior to that) and check out the sell by dates - these eggs can still sit on the shelf for a few more weeks."

Guidelines from the Food and Drug Administration (FDA) are apparently not strict with expiration dates, especially on egg products. In fact, the agency doesn't even require it, based on its Guide to Federal Food Labeling. The main requirements for egg products labeling include: product name, manufacturer's name, official identification, USDA approval number, ingredients statement, net weight statement and nutrition information.

The FDA only strictly requires "best before" labels on baby formula, while other food items are required based on state laws. Other companies also put the dates their by their own choice or discretion, according to Delish.

Below is an infographic from the USDA that explains store-bought egg labels further:

The thing to note is not the expiration date, but the packaging date, which is written in Julian date format. To convert Julian date format, use this. If you keep store-bought eggs inside the refrigerator for four or five weeks after the date on the packaging, they will remain safe for eating, Delish noted. At best, store eggs at45 degrees F temperature to retain freshness.