How to Tell if Chicken Egg is Fertilized?

Do you keep trying to hatch eggs in an incubator but to no avail? Your chicken eggs may not be viable because they’re simply not fertilized. So, how can you tell if the eggs in your incubator are fertilized or not?

There are a few simple ways in which you can figure out if a chicken egg is fertilized, and I’m going to cover all these methods below, so you can successfully hatch chicken eggs at home in an incubator.

What is a Fertilized Chicken Egg?

If you have a flock of chickens but no rooster, all the eggs these chickens produce will be unfertilized. That’s because a chicken will lay eggs with or without a rooster, but the eggs will be fertilized and hence viable only if there’s a rooster to fertilize them.

But how do roosters fertilize the eggs? By mating with the chickens, of course. When a rooster mates with a chicken, it does so by mounting the chicken, so that their cloacae are aligned.

Before mounting the hen, the rooster will perform a mating ritual of sorts by prancing around the hen while making clucking sounds.

The mating process doesn’t stop with the alignment of the cloaca. Once the rooster has steadied himself on the back of the hen and managed to align the cloacae, it will transfer its sperm via a bump located in the cloaca called a papilla.

This alignment of the cloacae, followed by the release of the sperm is called a ‘cloacal kiss’.

How does an Egg Become Fertile?

Once the sperm is released into the cloaca of the hen, it travels via the oviduct to the egg of the day, and that’s how the eggs become fertilized.

At this point you may wonder if every single egg needs to be fertilized like this to become viable? And the answer is no, not really.

The rooster can deliver anywhere between 100 million to 5 billion sperm, which can be stored in sperm pockets within the oviduct, and which remain viable for 4-5 days.

This means that even subsequent eggs on successive days will be fertilized after just a single mating.

There still may be situations in which despite there being a rooster in the flock, the eggs you try to incubate all turn out to be infertile.

This can happen for a number of reasons:

  • The rooster may not be mating with the hens at all. This can happen with new roosters that may need a period of accommodation before they start mating with the hens.
  • The rooster mates only with one hen. Some roosters may decide to mate only with a single hen and neglect mating with other hens or mate with them only sparingly.
  • There are simply too many hens to mate with and only a single rooster. If the flock is too big (e.g., over 16 hens) and you have a single rooster, you may need another rooster, so it’s not outnumbered.

Separate a hen that a rooster has chosen as its favorite to see if it will mate with other hens. Also, make sure the hen to rooster ratio is adequate, so all your hens get a chance to mate.

Candling the Chicken Egg

Let’s assume that a lack of a rooster is not a problem and the rooster is mating with various hens at various times, but you still have doubts whether the eggs you’ve chosen to incubate are fertilized.

The challenge here is how can you positively determine if an egg is viable or not, without actually cracking the egg, and thereby rendering it useless?

Candling the egg is one method you can use to check if an egg is fertilized. The way that this works is that you need to illuminate the eggs so that you can take a peek inside and identify any structures that indicate there’s a chick developing on the inside.

How does this illumination process work? And do you actually need a candle for it? No, a candle is not needed, despite the name of the procedure. It’s called candling an egg, because people used candles as a light source to check the eggs.

You can simply use a flashlight and go into a dark room to light the eggs and check for any formations inside that might suggest there’s a chick developing on the inside.

For candling to be precise, there are a few things that must happen first. You can’t candle the egg on the first few days of incubation. You need to wait at least 7 days for something to show up when an egg is lit.

You can use candling before the 7 days have passed only to make sure there aren’t any cracks or fissures on the eggs that might compromise the incubation.

At the 7-day mark, take the egg out of the incubator and put the flashlight against the egg to see if there’s anything developing on the inside.

What you should see at this point is several dark lines that if followed will lead to a small dark shape, which is the embryo.

The presence of these blood vessels and the embryo indicates that a chick is developing on the inside and the egg is fertilized.

If the egg is clear upon candling, it means it’s infertile and no chick will form on the inside.

If on day 7 you’ve noticed blood vessels and an embryo, you can safely assume that the egg is fertile. Some people will do a second candling on day 14 just to check if the chick is developing normally.

At the 14-day mark, you should see toes, eyes, and even a beak. This candling is not really necessary; the less time the eggs are away from the incubator, the better.

Anytime you want to remove an egg for candling, make sure to wash your hands first, and keep the eggs no longer than 30 minutes outside of the incubator.

Other Ways to Confirm Egg Fertilization

Aside from candling, there are two other ways to confirm egg fertilization, but unlike candling, one method actually involves cracking the egg to reveal the yolk.

– Cracking the Egg

This method is used to check the eggs that you’ll select for incubation, so it’s done prior to placing the eggs in an incubator.

The way this works is that you select 1-2 eggs from the hen and rooster you’re taking the eggs from and crack them open to check the yolk. You should do this in the days running up to the incubation.

If the yolk features a small white circle, then it means the egg is fertilized. This white circle is called the germinal disc and contains a single cell from the hen and a single sperm from the rooster.

Of course, once the egg is cracked, you can’t use it for incubation anymore, but it will give you an idea if the eggs from the same ‘batch’ are fertilized or not.

So, rather than waiting 7 days into the incubation to candle the egg, you crack open an egg from a batch to see if it’s fertilized.

– Floating the Egg

Floating the egg will not tell you if it’s fertilized or not, but it will tell you if it’s fresh or not. And that can also be helpful if you don’t know if eggs from a certain batch are suitable for incubation.

So, how does this test work? Simply take an egg and place it in a glass of water. If the egg sinks, it’s fresh. If the egg floats or tilts to the side, it’s rotten.


As you can see, there are ways to determine which eggs are suitable for incubation, which eggs are fertilized, and which are viable.

Fissures, cracks, taking the eggs out of the incubator for too long, and other seemingly minor issues can interfere with the viability of the eggs, so make sure to always handle them with care.

avatar James
Hey, I'm James, a hardworking homesteader for more than 30 years. I enjoy the feeling of accomplishment that comes from tending my flock. I've raised chickens and ducks for eggs and meat for many years. I also have experience with other poultry too. Learn more

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