It can be difficult to tell if an egg is okay for consumption or not because there aren’t any odor or visual clues to lead you in on its freshness.
A good way to tell a good egg from a bad egg is to submerge them in water. A fresh egg will sink to the bottom and a rotten egg will float. As eggs age, their liquidous inside begins to evaporate through the shell. This is what allows for a bad egg to float. The closer to the surface, the rottener the egg is.
SOURCE: Bigchill.com