Source: Idiot’s Guide to Baking by Alexandra Zayn

Hey beautiful bakers!
Everyone knows there is an expiration date on the side of the carton, but what if the eggs aren’t in the cartoon? What if you can’t read the date? Or what if you just have no way of knowing how old they are? There is an easy way to tell if the egg is fresh.
It’s super easy to do. All you have to do it place your egg in a clear glass. The cup should be at least double the size of the egg. Fill the glass with water and then place your egg in it.
If the egg rests at the bottom of the cup, the egg is fresh.
If the egg hovers at the bottom and sort of bounces a little, that means the egg is about a week old.
If the egg floats near the top but the largest tip of the egg is near the top, the egg is close to 3 weeks old.
If the egg floats completely to the very top, the egg is very old. That’s because sulfur built up inside the egg and you need to throw it out immediately.
I hope that helps if you find some random eggs laying around in your refrigerator. I think we all need to clean out our refrigerators more than we do sometimes.
Happy Baking Everyone!