I stumbled upon this great information from whatscookingamerica.net on how to determine if you should “chuke it” or “eat it”:
A general rule to follow is that any egg that looks or smells odd should not be used. If an egg is bad you will know it. Just smell the egg! Just crack each egg in a small bowl, smell it – your nose will tell you!
How to test if an egg is fresh
First Method:
Fill a deep bowl with water and carefully lower the egg into the water. A very fresh egg will immediately sink to the bottom and lie flat on its side. This is because the air cell within the egg is very small. The egg should also fee quite heavy.
As the egg starts to lose it freshness and more air enters the egg, it will begin to float and stand upright. The smaller end will lie on the bottom of the bowl, while the broader end will point towards the surface. The egg will still be good enough to consume.
However, if the egg fully floats in the water and does not touch the bottom of the bowl at all, it should be discarded, as it will most likely be bad.
Second Method:
Test the eggs freshness by breaking the egg onto a flat plate, not into a bowl. The yolk of a very fresh egg will have a round and compact appearance and it will sit positioned quite high up in the middle of the egg. The white that surrounds it will be thick and stays close to the yolk.
A less fresh egg will contain a flatter yolk, that may bread easily and a thinner white that spreads quite far over the plate.