Incubating chicken eggs: the process and development stages

An incubator does more than keep eggs warm. It needs to provide suitable temperature, moisture, fresh air and turning while a chick develops inside each viable egg.

Chicken eggs usually hatch at around 21 days, although timing varies. The best preparation is to understand your particular machine before placing valuable eggs inside it.

Before setting the eggs

Clean and disinfect the incubator according to its instructions, then let it dry. Run it empty for at least a full day to check that temperature and humidity are stable. Use an independent thermometer and hygrometer where possible, positioned as the manufacturer directs.

Choose clean, intact, normally shaped hatching eggs. Avoid cracked, leaking, badly soiled or unusually shaped eggs. Do not scrub or soak them as a routine preparation step.

Store hatching eggs with the pointed end down in suitable cool, stable conditions, and set them promptly. A normal household fridge is generally too cold for ideal hatching-egg storage. Let cool eggs approach room temperature before setting to reduce condensation.

Count day one after the eggs have completed their first 24 hours of incubation. Write down the setting date and time rather than relying on memory.

Temperature, humidity and turning

For many fan-assisted incubators, about 37.5°C is the usual starting temperature. Still-air machines need a different setup and measurement position. Follow your manufacturer's instructions rather than applying a fan-assisted setting to every incubator.

A common starting humidity range for chicken eggs is about 45–55% relative humidity, rising to around 65–70% for hatch. These are starting points, not universal targets. Shell characteristics, room conditions and incubator design affect moisture loss. Monitor air-cell growth or egg weight alongside the machine's guidance.

Turn eggs regularly until about day 18. If turning manually, many guides recommend at least three turns a day, using an odd number so eggs alternate overnight positions. Check that automatic turners actually move. Maintain ventilation throughout; never close vents merely to raise humidity.

Choosing between wet and dry incubation

You may hear keepers say they use “wet incubation” or “dry incubation”. These are informal descriptions of how they manage humidity, rather than two completely different ways of developing a chick.

Wet incubation usually means adding water to the incubator's channels or reservoirs during the first 18 days. The water evaporates and raises the humidity. It does not mean wetting, soaking or spraying chicken eggs.

Dry incubation usually means using little or no added water during that early period, provided the measured humidity and the eggs' moisture loss remain suitable. It does not mean zero humidity. Moisture is still present in the surrounding air, and the eggs themselves release water as they develop.

Why the choice matters

Eggs gradually lose water through tiny pores in the shell. As this happens, the air cell at the broad end grows. The developing chick needs an appropriate balance of remaining moisture and air-cell space for hatch.

If humidity stays too high, eggs may lose too little water and the air cell may remain too small. If it stays too low, they may lose too much water and the chick can become dehydrated. Either extreme can reduce hatch success.

The aim is to manage that moisture loss, rather than to commit to keeping a reservoir permanently full or permanently empty.

Which approach should you start with?

• For your first hatch, start with your incubator manufacturer's chicken-egg instructions. Use a reliable humidity reading and keep records. This gives you a clear starting point instead of changing several things at once.
• Consider adding less water if the incubator is already humid enough. In a humid room, adding water automatically may push humidity higher than needed. Confirm this with measurements and egg development rather than assuming Brisbane weather makes every hatch suitable for a dry approach.
• Add water when the readings and egg checks show it is needed. Air conditioning, seasonal changes and different incubators can produce much drier conditions. An empty reservoir is not a goal worth protecting if the eggs are losing too much moisture.

Check what is happening inside the eggs

Candle briefly at planned checks, such as days seven and fourteen, and compare air-cell growth with a suitable chicken-egg reference. Dark shells and irregular or damaged air cells can make this difficult, so do not rely on a single unclear view.

Weighing labelled eggs at setting and at planned checks is another way to follow moisture loss. Use a suitable accurate scale and compare the trend with a chicken-egg weight-loss guide that clearly states its endpoint. A target for day 18 is not interchangeable with one for pipping or hatch.

If eggs are losing moisture too quickly, humidity generally needs increasing; if they are losing too little, it generally needs reducing. Make measured adjustments, keep temperature steady and maintain the ventilation specified for your machine. Do not block vents to trap moisture: developing embryos need fresh air.

Dry incubation does not mean a dry hatch

Even when little or no water was needed early on, humidity usually needs increasing for the final hatching stage. Follow the incubator's lockdown instructions, generally from around day 18 for chicken eggs. Adequate hatching humidity helps prevent exposed membranes drying out around a pipping chick.

Do not leave the incubator dry throughout hatch simply to stay with the method's name. Equally, do not mist eggs or keep opening the lid to chase every small fluctuation. Check equipment, follow the trend and make changes for a reason.

A useful rule: Let your machine's instructions, measured conditions and the eggs' progress guide the water level. One keeper's successful dry hatch does not prove that the same setup will suit your room, season or batch of eggs.

Days one to three: the earliest development

The embryo begins developing its body structures, circulation and heartbeat very early. You will not see all of this through the shell.

Keep conditions steady and resist the urge to candle repeatedly. The egg needs consistent care more than frequent inspection.

Days four to seven: development becomes easier to see

By around day seven, candling may reveal a network of blood vessels and a darker embryo in a developing egg. Dark or heavily pigmented shells can be much harder to assess.

Use a bright egg candler in a dim room, handle gently and keep checks brief. If an egg looks clear but you are uncertain, mark it and recheck after several days. Do not discard a doubtful egg based only on a difficult early view.

An egg that smells bad, leaks or shows obvious contamination needs careful removal. Do not hold a suspect egg near your face or crack it open indoors.

Days eight to fourteen: rapid growth

The chick becomes larger and more recognisable, with limbs, a beak and developing feathers. A day-14 check can help you compare growth and the air cell with your earlier observations.

A blood ring or loss of previously visible development may indicate an embryo has died. Ask an experienced hatcher for help if you are unsure. Candling cannot diagnose every cause of failure.

Days fifteen to eighteen: preparing for hatch

The chick fills more of the shell, so less light passes through. By about day 18, stop turning and remove or disable the turning mechanism as instructed. Prepare the incubator for hatch and adjust humidity according to its guidance.

This stage is often called lockdown. It means avoiding unnecessary disturbance, not stopping ventilation or ignoring equipment failure.

Days nineteen to twenty-one: pipping and hatching

The chick first breaks into the air cell, then makes an external pip in the shell. It may rest for a long time before turning and opening the shell further.

Do not peel shell away because progress seems slow. The chick may still be absorbing yolk and closing blood vessels; helping too early can cause fatal bleeding. Do not use a float test to decide whether an unhatched egg is alive.

Keep a record of what happens, including temperature problems and hatch timing. Before assuming late eggs have failed, seek advice and assess them carefully.

Browse fertile eggs at Chuckles Chickens once your equipment is ready. Good eggs are a starting point; careful handling and incubation still determine much of the outcome.

Sources and further reading: Brinsea: humidity and egg weight loss; University of Maryland: hatching eggs at home; Mississippi State: incubation factors; Mississippi State: temperature requirements; Mississippi State: the avian embryo; Mississippi State: hatchery management; University of Maine: hatching your own chicks.