How To Candle Eggs: Definitive Day-By-Day Guide

Candling eggs is one of the most exciting parts of hatching chicken eggs.

It is also one of the most important.

Candling was once done with a candle but these days most people use a flashlight.

Egg candling is a simple way to monitor the growth and development of your chicks whilst they are still inside their eggs.

In this article we explain how to candle eggs, what to expect day by day and much more…

What is Egg Candling?

How To Candle Eggs

Egg candling is simply the process of using a small, bright light to look through the shell and inside the egg.

This is most easily done in a completely dark room.

Candling eggs is an important step during incubation as it lets you check for fertile eggs, as well as embryo viability and progress. It gives handlers the opportunity to look for clues and make their own judgments and decisions when it comes to discarding eggs throughout the incubation process.

Unfortunately, the hatch rate of a batch of eggs is very rarely 100%. Most of the time this is no fault of the person incubating the eggs. Some eggs simply come to you unfertilized and will never produce an embryo to begin with. Most good hatcheries will refund these eggs.

These types of eggs are called yolkers.

You also have quitters.

This is when a fertilized egg will stop developing in the middle of the incubation process.

Yolkers and quitters can be identified through candling eggs and should be removed from the incubator and discarded to avoid rotting and any messes that come with it. We cover this in more detail in our incubator guide.

Do not be discouraged if you have any yolkers or quitters as the average hatchability of set eggs is around 75-80%.

How To Candle Eggs

Candling Eggs

First of all you will need a bright light source.

Farm and poultry supply stores often sell specialized egg candlers, but it is quite simple to make your own. After all, candling eggs was first done with a candle!

A small, bright flashlight with a 1-inch diameter hole to allow for directed light is ideal.

You will also need a dark room.

Once you have got your equipment ready, the first step is to wash your hands.

Only once your hands are clean can you start candling eggs.

You should take the flashlight in one hand and the egg in another. Hold the egg upright and bring the flashlight right underneath the egg. Try not to hold the light source directly against the egg and also make sure not to candle with the pointed side of the egg facing up.

A fertilized egg by day 7 should have a dark spot surrounded by blood vessels, while an unfertilized egg will appear empty and clear with the exception of the egg yolk. This is observed by shining your light beneath the wider end of the egg and slowly rotating the egg.

When candling your eggs it can be a bit confusing as to what you are looking at.

You should make sure you are comfortable with the basic anatomy of an egg and can spot the air sac, pores, yolk, blood vessels, the red yolk ring, and, last but not least, the actual embryo.

When Should You Candle Eggs? (Candling Eggs Milestones)

Egg Candling Chart

There are two key milestones when you need to candle your eggs.

These are day 7 and day 14 of the incubation process.

During these key milestones you can check on the progress and viability of your eggs. Candling regularly is not only crucial for identifying unviable eggs throughout the incubation process, but the more you do it, the better you will get at it.

Some people like to candle their eggs before they are even placed in the incubator.

Candling at this point makes sure that all eggs placed within the incubator do not contain any cracks. Keep in mind that damaged eggs are susceptible to bacterial growth and rotting, so these eggs should be discarded before you start incubating your eggs.

Eggs that have deformed shells should also be removed as they can lead to many difficulties when it comes time for chicks to hatch.

Day 7: First Candling

After 7 days in the incubator you should be able to see some signs of life.

Signs of development will typically appear as a dark spot surrounded with numerous blood vessels. If this is what you see, then congratulations, your egg is viable and contains a chicken embryo.

An unfertilized egg will not show any development at this stage and will simply appear clear when candled.

If upon candling, an egg seems to contain a thin ring with an irregular looking lining, that would be considered a blood ring. When an embryo is no longer viable, blood will seep away from it forming this ring. Dead embryos will typically look like a murky, dark shadow.

Unfortunately, any eggs containing blood rings are not viable.

Any clear eggs or eggs containing blood rings should be removed from the incubator at this point to avoid any rotting.

If at this point you are unsure of the viability of any of your eggs, you should mark them and keep a watchful eye on them. Watch them for any foul smells or a dark interior as these signs suggest they are filled with bacteria.

Day 14: Second Candling

By day 14 viable and developing eggs will be hard to candle as the majority of the egg should now be taken up by the chick.

Instead of looking like a dark spot with a web of blood vessels, as it does on day 7, it will have a cloudy-looking dark spot with an increased number of blood vessels.

This second candling gives hatchers the opportunity to not only recheck the viability of their eggs, but also check the eggs’ weights as well as the size of the air cells within the eggs.

You should also be able to spot the air cell when candling on the wide end of an egg. Overtime, as the embryo grows and moisture escapes the egg the air pocket should grow in size as well.

Day 18: Final Candling (Optional)

Some people will candle their eggs a third time on or before day 18, just before the eggs enter the lockdown period.

Candling one more time gives hatchers a final opportunity to monitor any development as well as get a final weight for the eggs. However, you should try to minimize the number of times you candle your eggs to decrease the number of times the incubator is opened and the humidity levels are disrupted.

Unless you suspect something is wrong, it is recommended you do not candle your eggs a third time.

Egg Anatomy

Egg Candling Tips

One of the most important things to remember when candling eggs is to keep a clean and sanitary environment.

Egg shells are incredibly porous so dirty hands or a dirty flashlight can easily contaminate an egg and kill any viable embryo that may be developing inside.

You should wash your hands and flashlight before they come into contact with your eggs. This will minimize the number of possible contaminants coming into contact with the egg.

Next, you should candle your eggs in an environment similar to the incubator.

Exposing an egg that was just at 99.5°F to significantly cooler or hotter temperatures can lead the egg to sweat which weakens the eggs natural protective coat. Any alteration to the bloom can allow bacteria to enter the egg through pores, which will contaminate the egg’s interior and affect the embryo’s development.

Finally, make sure not to candle your eggs too often.

While the actual process of candling does not harm the egg or the embryo, the less handling of the eggs that occurs during the incubation process the better.

Less handling means fewer opportunities for bacteria or other nasty microbes to come into contact with your precious eggs.

You should also limit the candling process to no more than 30 minutes, with 10 minutes being ideal. This helps to make sure that the temperature within the egg does not fluctuate too much.

Common Mistakes When Candling Eggs

For first time hatchers it can be difficult to know whether or not an egg is viable.

This leads to the two biggest mistakes that people make.

1. Not removing unviable eggs

A common mistake is not removing unviable eggs.

If you leave these unviable eggs inside the incubator then pressure will build up and they will eventually explode.

You should closely monitor these eggs for any questionable smells, substances coming out of them, or cloudy, dark spots on the inside. These features all indicate that bacterial contamination has occurred and the egg should be removed immediately.

2. Discarding viable eggs

Egg candling early on brings its benefits but can also lead to some doubt, especially for first time hatchers.

Sometimes eggs will not show much development by day 7.

In an effort to avoid any rotting and unviable eggs, these slower growing viable embryos are removed.

When in doubt there is no reason that an egg cannot stay in an incubator for a couple more days as long as it is being monitored and checked regularly.

Signs of an Egg Gone Bad

Most embryo deaths occur within the first few days of incubation.

This usually happens due to inadequate temperatures leading up to the incubation, excessive movement of the egg, or, at no fault of the owner, genetic issues making the embryo incompatible with life.

An egg gone bad can also be due to the presence and contamination of bacteria within your egg. As the bacteria begin to grow and multiply within your egg, the embryo will no longer grow.

As bacteria grow within the no longer viable egg, gas is produced as a byproduct which slowly builds pressure within the egg. If the egg is not removed from the incubator, then the pressure becomes too great and the egg explodes.

Being able to spot and remove bad eggs within your incubator is very important to keep your remaining eggs uncontaminated and healthy.

There are a few early warning signs of an egg gone bad that can be easily spotted.

These signs include a nasty odor, a red blood ring upon candling, and discolored oozing coming from the egg.

  • Odor: The strong, rotting odor coming from bad eggs is pretty hard to miss. Any eggs with an odor of any kind should immediately be removed from the incubator.
  • Blood Ring: An embryo that has stopped developing and become unviable will have blood seep out from it creating a blood ring which can easily be seen when candling.
  • Oozing: Viable and healthy eggs will never ooze. Any oozing egg should be discarded immediately as this is a sign of immense pressure buildup in the egg and a sign that the egg could explode at any moment.

Frequently Asked Questions

Can candling harm eggs?

The simple answer is no.

Candling does not harm your eggs.

If a broody hen can leave her nest for short periods of time every day and successfully hatch an entire batch of eggs, then it is safe for you to take your eggs out of their incubator to candle them for a brief moment.

Just make sure to be mindful of temperature, humidity, and cleanliness when candling.


With just a few pieces of equipment, a dark room, and a bit of spare time, you can candle your eggs.

Candling chicken eggs is not only fun and rewarding, it also lets hatchers modify the incubation process as needed and can lead to an increased hatch rate if done correctly. Being able to see if your eggs contain any blood spots or hairline cracks will make sure you are safely incubating eggs and that there are no unhappy surprises down the line.

As long as you are gentle and maintain a sanitary environment throughout the candling process, egg candling will prove to be a helpful tool.

With enough research and practice it only gets easier too.

Are you ready to start your hatching journey? Let us know in the comments section below…

Chris Lesley Bio Picture
Chris Lesley has been Raising Chickens for over 20 years and is a fourth generation chicken keeper. She can remember being a young child when her grandad first taught her how to hold and care for chickens. She also holds a certificate in Animal Behavior and Welfare and is interested in backyard chicken health and care.

Be the first to comment

Leave a Reply

Your email address will not be published.