How to tell if my incubating eggs are fertilized and therefore likely to hatch? -
incubating eggs

How to tell if my incubating eggs are fertilized and therefore likely to hatch?

Incubating eggs can be a thrilling and rewarding experience, whether you’re a hobbyist, a small-scale farmer, or even a classroom teacher demonstrating the miracle of life to students. However, one of the key aspects of successful incubation is ensuring that your eggs are fertilized and have the potential to hatch.

Unfertilized eggs will never develop into chicks, making it crucial to identify fertility early in the incubation process.

In this comprehensive guide, we’ll explore the methods and techniques used to determine if your incubating eggs are fertilized and likely to hatch.

Understanding Egg Fertilization

Before diving into the methods of identifying fertilized eggs, it’s essential to understand what fertilization entails. Fertilization occurs when a rooster mates with a hen, transferring sperm that will fertilize the eggs within the hen’s reproductive system. Once fertilized, these eggs contain a developing embryo, which, under the right conditions, will grow and eventually hatch into a chick.

Key Terms:

  • Fertilized Egg: An egg that has been fertilized by sperm and contains a developing embryo.
  • Unfertilized Egg: An egg that has not been fertilized and will not develop into a chick.
  • Candling: A method used to observe the contents of an egg using a bright light source.

Methods to Determine Fertilized Eggs

There are several methods to determine if your incubating eggs are fertilized, each with its own advantages and specific use cases. Here, we’ll explore these methods in detail.

1. Visual Inspection Before Incubation

Before placing the eggs in an incubator, a visual inspection can sometimes indicate fertilization, though this method is less reliable than others. Fertilized eggs often have a small white spot or bullseye on the yolk, known as the blastoderm. This is where the embryo begins to develop.

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How to Inspect:

  1. Crack a Few Eggs: Select a few eggs from your batch and gently crack them open.
  2. Observe the Yolk: Look for a small white spot on the yolk. A fertilized egg will have a white spot with a bullseye appearance, indicating the presence of an embryo.
  3. Practice: It takes practice to accurately identify the blastoderm, as it can sometimes be difficult to distinguish from the blastodisc (a white spot found in unfertilized eggs).


  • Simple and straightforward.
  • Requires no special equipment.


  • Wastes eggs that could potentially be incubated.
  • Less reliable than other methods.

2. Candling

Candling is a widely used and effective method to determine egg fertility during incubation. This technique involves shining a bright light through the egg to observe its internal contents. Candling is best performed in a dark room to maximize visibility.

How to Candle:

  1. Prepare a Candling Light: Use a specialized egg candler or a bright flashlight.
  2. Darken the Room: Ensure the room is dark to enhance visibility.
  3. Hold the Egg: Hold the egg gently but securely between your thumb and fingers.
  4. Shine the Light: Position the light at the broader end of the egg, allowing it to shine through.
  5. Observe: Look for signs of development, such as veins, a dark spot (embryo), or movement.

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When to Candle:

  • Day 7-10: At this stage, veins should be visible, and you may see a small, dark spot (embryo).
  • Day 14: The embryo should be more developed, with more prominent veins and movement.
  • Day 18-21: The egg will appear mostly dark, indicating the chick is filling up the egg.


  • Non-invasive and does not harm the egg.
  • Allows ongoing monitoring of embryo development.


  • Requires a good candling light and some practice to interpret correctly.
  • Can be less effective for darker-shelled eggs.

3. Floating Test

The floating test, also known as the water test, can be used to assess the viability of eggs late in the incubation period. This test relies on the principle that developing embryos produce gases that can cause the egg to float or bob in water.

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How to Perform the Floating Test:

  1. Fill a Bowl with Warm Water: Ensure the water temperature is close to the incubator’s temperature (around 99-101°F or 37-38°C).
  2. Gently Place the Eggs: Carefully place the eggs in the water one at a time.
  3. Observe Movement: Viable eggs may show slight movements or bobbing, indicating the presence of a living embryo. Non-viable eggs will typically sink or remain still.


  • Simple and quick.
  • Can provide a final check on egg viability before hatching.


  • Should only be used late in incubation to avoid disturbing developing embryos.
  • Not as reliable as candling for early-stage identification.

4. Monitoring Incubation Progress

Throughout the incubation period, there are several signs that can indicate the viability of the eggs:

Temperature and Humidity:

  • Maintaining Proper Conditions: Ensure the incubator maintains a consistent temperature (99-101°F) and appropriate humidity levels (45-50% initially, increasing to 65-70% in the final days).
  • Egg Position: Eggs should be positioned correctly and turned regularly (if not using an automatic turner) to prevent the embryo from sticking to the shell.

Observing Developmental Milestones:

  • Day 7: Veins and a small embryo should be visible during candling.
  • Day 14: More pronounced embryo movement and development.
  • Day 18: Eggs should not be turned anymore, and higher humidity should be maintained for hatching.


  • Provides ongoing feedback on egg health and development.
  • Helps identify potential issues early.


  • Requires diligent monitoring and record-keeping.
  • Incorrect conditions can negatively impact all eggs in the incubator.

5. Post-Hatch Analysis

After hatching, you can further assess egg fertility and development by examining any unhatched eggs. This post-hatch analysis can help improve future incubation practices.

How to Perform Post-Hatch Analysis:

  1. Open Unhatched Eggs: Carefully open any unhatched eggs to observe their contents.
  2. Identify Developmental Stage: Determine at what stage development ceased (early, mid, or late incubation).
  3. Assess Causes: Look for potential causes of non-hatch, such as bacterial contamination, improper incubation conditions, or genetic issues.
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  • Provides valuable insights for improving future hatch rates.
  • Helps identify common issues and areas for improvement.


  • Only applicable after the incubation period.
  • May not always clearly indicate the cause of non-hatch.

Best Practices for Incubation

To maximize your chances of successfully hatching fertilized eggs, follow these best practices:

Choosing the Right Eggs:

  • Source Quality Eggs: Obtain eggs from a reliable source with healthy, well-nourished hens and roosters.
  • Egg Handling: Handle eggs carefully to avoid damaging the shells or introducing contaminants.

Preparing the Incubator:

  • Clean Thoroughly: Clean and disinfect the incubator before use to prevent bacterial contamination.
  • Calibrate Equipment: Ensure the incubator’s thermostat and hygrometer are accurate.

Maintaining Optimal Conditions:

  • Temperature: Keep the temperature steady at 99-101°F.
  • Humidity: Maintain appropriate humidity levels throughout incubation.
  • Turning Eggs: Turn eggs at least three times a day if not using an automatic turner.

Regular Monitoring:

  • Candle Eggs: Candle eggs at key stages to monitor development.
  • Record Observations: Keep detailed records of temperature, humidity, and developmental progress.

Preparing for Hatching:

  • Increase Humidity: Increase humidity during the final days of incubation to aid hatching.
  • Lockdown Period: Do not open the incubator during the final days to maintain stable conditions.

Common Issues and Troubleshooting

Even with the best practices, issues can arise during incubation. Here are some common problems and troubleshooting tips:

Infertile Eggs:

  • Candling Results: Infertile eggs will appear clear when candled, with no visible veins or embryo.
  • Solution: Remove infertile eggs from the incubator to prevent them from contaminating the others.

Early Embryo Death:

  • Causes: Can be due to bacterial contamination, improper temperature or humidity, or genetic issues.
  • Solution: Ensure proper incubator sanitation and stable conditions.

Late Embryo Death:

  • Causes: Often due to improper humidity levels, especially during the final days.
  • Solution: Monitor and adjust humidity levels carefully.

Chicks Not Hatching:

  • Causes: Can be due to weak embryos, shell positioning, or improper hatching conditions.
  • Solution: Ensure optimal humidity and avoid opening the incubator during hatching.


Determining whether your incubating eggs are fertilized and likely to hatch involves a combination of methods, including visual inspection, candling, the floating test, and careful monitoring of incubation conditions.

By understanding the signs of fertility and following best practices, you can maximize your chances of successfully hatching healthy chicks. Remember, successful incubation is both a science and an art, requiring attention to detail, patience, and a willingness to learn from each hatch.

Author: Adewebs

David is a seasoned farmer with over 8years experience on the field and teaching. He has about 20 acres of Palm farm, 10acres of livestock farm where he spent most of his time tending and caring for his farm. He offer profffesional services and consultancy services to clients who are interested in venturing into farming.

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