To tell if an egg is fertilized, the methods differ depending on whether you mean a human egg or a bird (e.g., chicken egg):

For Human Eggs

• Fertilization itself usually has no obvious physical symptoms at the moment it occurs. Most women do not feel when an egg is fertilized

• A fertilized egg (zygote) travels to the uterus and implants about 6-10 days after fertilization. Implantation can cause subtle signs such as light spotting (implantation bleeding), mild cramping, abdominal bloating, nausea, or an increased urge to urinate

• These symptoms are not definitive proof of fertilization, and their absence does not mean fertilization hasn't occurred. The most reliable way to confirm pregnancy (and thus fertilization) is a pregnancy test after a missed period

For Chicken Eggs

• Fertilized chicken eggs show a visible "bullseye" or a larger, less dense white spot (germinal disc) on the yolk, often surrounded by a darker halo. Unfertilized eggs have a small, dense white dot on the yolk

• Another method is candling: holding the egg up to a bright light in a dark room. Fertilized eggs show spider-like blood vessels and a dark embryo shape inside the yolk, while unfertilized eggs appear clear or uniformly translucent

• Incubating the egg for several days and then candling can confirm embryo development. If a chick grows inside, the egg was fertilized

Summary Table

Egg Type| How to Tell if Fertilized| Notes
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Human Egg| Implantation signs: light spotting, cramping, bloating; pregnancy test| Fertilization itself not felt; test after missed period is most reliable
Chicken Egg| Visual inspection of germinal disc; candling to see veins and embryo| Incubation can confirm by chick development

In short, for humans, fertilization is confirmed indirectly by implantation signs and pregnancy tests. For chicken eggs, visual inspection of the yolk spot and candling are practical ways to identify fertilization.