Crack the egg open and look for a small white bullseye-like spot on the yolk
A fertilized egg may show a clear germinal disc with a ring or target shape
Unfertilized eggs usually have a small, solid white dot on the yolk
Candle the egg with a bright light to check for development after incubation has started
Look for blood vessels or a developing embryo during candling
Fertilized eggs that have not been incubated often look the same as unfertilized eggs
The only reliable way to confirm fertilization is to incubate and then candle for development