You cannot tell by looking at a fresh egg alone
Fertilized eggs look the same as unfertilized eggs before incubation
Check for a bullseye-shaped white spot on the yolk after cracking the egg
A fertilized egg may show a small white ring or target-like spot on the yolk
Use candling during incubation to see blood vessels and embryo development
Look for embryo growth after a few days of incubation
A fertilized egg will develop veins and a dark spot as it incubates
An unfertilized egg will not develop veins or an embryo
In store-bought eggs, fertilization is very unlikely unless they came from a rooster-involved flock
Only incubation can confirm fertilization through development