How to tell if chicken eggs are fertile? (1 classic method)
In this article, we will explore the question, “How to tell if chicken eggs are fertile?” We will also discuss the common biological aspects associated with a fertile egg.
How to tell if an egg is fertile?
To determine if an egg is fertile, you can look for a specific characteristic. A fertile egg will typically have a small white circle on the yolk (1 and 2).
This circular shape indicates the presence of a cluster made up of fertilized cells, which has the potential to develop into a new chick (2).
By observing this distinct feature, you can differentiate between fertile and infertile eggs.
How does the candling method help to determine if an egg is fertile?
When the eggs are in an advanced stage of incubation, the candling method can be used to determine if an egg is fertile. After incubating the eggs, go to a dark room and shine a light at the wide end of the egg (2).
The light will reveal a dark patch in the middle of the egg, surrounded by a network of veins, or it may appear opaque. If you do not see any veins and only spot the egg yolk, it indicates that the egg is not fertile (3).
The candling method is an effective way to monitor the stages of the incubation process. It is important to note that the incubation process lasts for a duration of 21 days (2 and 3).
How are eggs formed in chickens?
A chicken lays eggs whether it has mated or not. Once matured at six months of age, a chicken will begin laying eggs almost every day. Chickens have an ovary and an oviduct responsible for egg development and formation (3).
The egg formation starts in the ovary and then moves to the oviduct. If fertilization occurs, the sperm infuses into the yolk, making the egg fertile.
Without fertilization, the egg continues through the oviduct, where the yolk is surrounded by egg white, followed by the inner and outer shell layers.
The egg then leaves the oviduct and enters the uterus, where the outer hard shell forms. The fully formed egg then exits through the cloaca (1 and 3).
How is a hen’s egg produced and fertilized?
After reaching six months of age, a mature hen begins laying eggs on a near-daily basis, depending on the time it takes for the egg to fully develop in her reproductive tract.
The process begins in the ovary and moves to the oviduct. If the hen has been mated, the sperm mixes with the yolk, resulting in a fertile egg. If not, fertilization does not occur (2 and 3).
Instead, the egg continues through the oviduct, where the yolk is enveloped by egg white, followed by the formation of the inner and outer shell (2 and 3).
Upon entering the uterus, the outermost hard shell is created. Finally, the fully-formed egg is expelled through the cloaca.
How does fertilization occur in a chicken egg?
A chicken egg can be either fertile or infertile. If a hen has mated with a rooster or undergone artificial fertilization prior to laying the egg, it is likely to be fertile (1 and 3).
During copulation, the rooster’s sperm travels through the hen’s oviduct to fertilize the yolk of the egg. The sperm can remain in the hen’s reproductive tract for a couple of weeks until fertilization occurs.
The process of fertilization takes over a week as the sperm travels to the oviduct. It’s worth noting that eggs laid by the hen will remain fertile for two to three weeks after mating (1).
Is it safe to consume fertile eggs?
Yes, it is safe. Incubation is essential for a fertile egg to hatch into a chick; otherwise, it remains unviable.
A fertile egg contains a small white speck called the blastoderm within the yolk. The blastoderm needs to be stored at 85°F or 29°C for a day to develop into an embryo (1).
Store-bought eggs (fertile and infertile) are typically and safe to consume unless incubated. After 3-4 days of incubation, a fertile egg begins the process of chick formation (3).
Without incubation, the embryo remains as a stagnant blemish on the yolk. Visual cues and candling may not conclusively determine fertility, necessitating cracking open the egg for confirmation (3).
Are fertile eggs more nutritious?
Fertilized eggs do not have nutritional differences compared to unfertilized eggs. They are safe to eat. Almost all eggs produced commercially are infertile. Roosters do not have to be present for hens to lay eggs (1).
In the poultry meat industry, when there is an excess of hatching eggs, eggs from broiler breeder flocks can be sold for human consumption (1).
However, the embryo does not develop in fertilized eggs unless they are subjected to incubation conditions (1).
Other FAQs about Eggs which you may be interested in.
In this article, we have addressed the question, ‘How to tell if chicken eggs are fertile?’ A fertile egg usually has a small white circle on the yolk. Both fertile and infertile eggs are safe to eat unless incubated.
2. Carey, J. B.; Cartwright, A. L.; Farnell, M. B.; Davis, M. Poultry Q and A Agrilife extension Texas A and M System. [Internet]. [cited 2023 Jul 06]. Available from:
3. Tazawa H, Mikami T, Yoshimoto C. Respiratory properties of chicken embryonic blood during development. Respir Physiol [Internet]. 1971;13(2):160–70. Available from: