Incubating Chicken Eggs—Temperature, Humidity, Turning and Candling

July 29, 2026

Successful incubation depends on controlling temperature, egg moisture loss, turning, ventilation and sanitation.

Incubation settings are starting points. Always consider the incubator manufacturer’s instructions and your own hatch records.

Preparing the Incubator

Run the incubator empty for at least 24 hours before setting valuable eggs.

During the test:

Confirm that temperature remains stable.
Check humidity.
Make sure the automatic turner operates correctly.
Compare the incubator display with independent instruments.
Place measuring equipment at the correct egg height.
Look for hot and cool areas.
Make sure ventilation openings are clear.

A separate calibrated thermometer and hygrometer can identify inaccurate incubator displays.

Place the machine in a room protected from:

Direct sunlight
Draughts
Heaters
Air conditioners
Large temperature changes
Children and pets

Incubation Temperature

Common starting temperatures for chicken eggs are:

Forced-air incubator: approximately 37.5°C
Still-air incubator: approximately 38.5°C, measured at the top of the eggs

Still-air and fan-assisted incubators are measured differently. Follow the directions for your machine.

Consistently high temperature can cause:

Early hatching
Weak chicks
Poor navel healing
Malformations
Increased embryo mortality

Consistently low temperature can cause:

Delayed hatching
Weak chicks
A wide hatch window
Late embryo deaths

Brief fluctuations are less important than a persistently incorrect average temperature. Avoid constantly changing the controls in response to every temporary variation.

Humidity and Egg Moisture Loss

Humidity controls how quickly water leaves the egg through shell pores.

There is no single perfect humidity percentage for every situation. Moisture loss is affected by:

Shell porosity
Egg size
Egg age
Altitude
Incubator airflow
Room humidity
Breed and bloodline

A commonly used starting range during Days 1–18 is approximately 40–55% relative humidity, followed by higher humidity during hatch.

However, air-cell growth and egg-weight loss are more useful than following one number blindly.

For a more objective method:

Weigh a representative group before setting.
Reweigh them at regular intervals.
Calculate moisture loss.
Adjust water surface area gradually.

Many incubation programs aim for approximately 11–13% egg-weight loss by transfer, although the appropriate target can vary.

“Dry incubation” should not be treated as automatically superior. Very low humidity can overdry the egg and enlarge the air cell excessively. High humidity can prevent sufficient moisture loss and leave the air cell too small.

Use results from your own machine to make careful adjustments.

Ventilation

Embryos take in oxygen and release carbon dioxide. Their oxygen requirement increases substantially near hatch.

Never close incubator vents simply to raise humidity.

Instead, increase the exposed water surface while maintaining the airflow recommended by the manufacturer.

Poor ventilation can contribute to chicks pipping internally or externally and then dying before completing the hatch.

Turning Eggs

Turning helps prevent the developing embryo and membranes from adhering incorrectly.

Turn eggs:

At least three times each day when turning manually
Preferably an odd number of times daily
Gently, without shaking
Until approximately Day 18

An automatic turner is helpful, but confirm that it actually moves. A running motor does not always mean the trays are turning correctly.

Stop turning at lockdown, generally around Day 18 for chicken eggs.

Setting Egg Position

Follow the incubator design.

In upright trays, eggs are generally positioned with the broad end up and narrow end down.

When eggs are incubated horizontally, position them on their sides and turn them from side to side.

Do not place eggs upright with the narrow end facing upward.

Candling Chicken Eggs

Candling allows you to assess development without opening the egg.

Useful times include:

Around Day 7
Around Day 14
Optionally at lockdown to assess air cells

During early candling, a developing egg may show:

A network of blood vessels
A small dark embryo
Movement
Progressive darkening

A clear egg may be infertile or may contain an embryo that died very early.

A blood ring can indicate early embryo death.

Dark brown, olive and blue eggs may be difficult to interpret. Use a strong light in a dark room and keep the examination brief.

Do not discard an uncertain egg after one unclear candling. Mark it and recheck several days later unless it is:

Leaking
Cracked
Producing a foul smell
Showing obvious contamination

Lockdown

Lockdown usually begins around Day 18.

At lockdown:

Stop turning.
Remove or disable the automatic turner.
Position eggs for hatch.
Increase humidity.
Maintain ventilation.
Avoid unnecessary opening.
Ensure the brooder is ready.

The term “lockdown” does not mean ignoring a dangerous equipment failure. Intervene if the incubator malfunctions, but otherwise minimise unnecessary disturbance.