Chicken egg incubation: the complete 21-day guide

A successful hatch does not come from one magic setting. It depends on a complete chain: egg quality, machine stability, temperature, humidity, ventilation, turning, hygiene and patience during hatch.

This guide covers chicken eggs in a small artificial incubator. The normal cycle is about 20 to 21 days, according to the FAO small-scale poultry guide. Instructions for your specific incubator always take priority.

The cycle at a glance

Period	Goal	Main actions
Before setting	Stabilise the machine and select eggs	Clean, test and compare with an independent instrument
Days 1–7	Support steady early development	Maintain settings, turn eggs, first candling around day 5–7
Days 8–14	Growth and control	Continue turning, monitor water and ventilation, second candling around day 13–14
Days 15–18	Prepare for hatch	Watch heat, maintain airflow, stop turning after day 18
Days 19–21	Hatch	Raise humidity according to the manual, open vents, stop turning and limit opening

1. Identify the incubator type

A forced-air incubator uses a fan to distribute heated air. A still-air incubator has larger temperature differences between the top and bottom of the chamber.

Mississippi State University Extension gives 100°F, about 37.8°C, as a reference for a forced-air incubator and notes that still-air machines generally require a reading 2–3°F higher at the recommended measuring position. This is why a setting should never be copied without knowing the machine type and sensor location.

Always use:

• the manufacturer’s setting for the specific model;
• an independent thermometer at the recommended height;
• several hours of empty testing before eggs are added.

2. Prepare the machine before day one

Place the incubator on a stable surface, protected from direct sunlight, rain, dust and draughts. Clean trays and the chamber according to the manual, then operate the machine until readings remain stable.

Before starting, check:

• the display against the control thermometer;
• actual movement of the automatic tray;
• water level and access to the reservoirs;
• ventilation openings;
• transfer to 12V backup if the machine supports it;
• high- and low-temperature alarms.

An alarm during testing is useful. It is better to understand it before eggs are loaded.

3. Select and store eggs

Choose clean, normally shaped eggs without cracks or major deformity. Handle them with clean hands. Do not set an egg with a broken or unusually porous shell.

When eggs must be held before incubation, the FAO small-scale guide recommends storage for no more than about seven days in cool, humid conditions. Extended storage generally reduces hatch potential.

Allow eggs to warm gradually toward room temperature before placing them into a hot machine, reducing condensation on the shell.

4. Days 1–7: stability and first candling

The first days require consistency. Do not change the setpoint in response to every small display fluctuation. Watch the trend over time and compare it with the independent instrument.

For manual turning, Mississippi State University Extension recommends turning eggs at least four to six times per day. An automatic system must also be checked visually: hearing the motor does not prove that the tray is actually moving.

First candling can be done around day 5 to day 7. In a dark room, a suitable light may reveal blood vessels and a dark developing area. Work quickly to limit unnecessary cooling.

An egg that appears clear may be infertile or too early to judge. If uncertain, mark it and check again after a few days rather than making an immediate decision.

5. Days 8–14: growth, water and ventilation

Continue turning with the same regularity. Monitor water without blocking vents. Embryos consume increasing amounts of oxygen, so ventilation must not be sacrificed simply to retain heat.

A second candling around day 13 or day 14 helps compare development, identify some early failures and observe the changing air cell.

Remove an egg that leaks, smells bad or presents a clear contamination risk. Do not open a suspect egg in the room where the incubator is operating.

6. Understand humidity without chasing one universal number

Humidity controls water loss from the egg. If it remains too low for too long, excessive water may be lost. If it remains too high, water loss may be insufficient and the air cell may remain too small.

There is no single number that works for every small incubator. Results depend on:

• machine design and water-surface area;
• sensor calibration;
• room humidity;
• shell porosity;
• altitude and ventilation.

Begin with the manufacturer’s instructions. Then observe the air cell during candling and, if you understand the method, weight loss from a representative group of eggs. Change one variable at a time and keep records.

7. Days 15–18: prepare for hatch

Growing embryos produce more heat and require more air. Confirm that vents remain clear. Never cover an incubator in a way that blocks its air inlets.

After day 18, stop turning chicken eggs. Remove or lock the turning tray according to the manufacturer’s procedure and place eggs on the intended hatching surface.

Use this transition to fill the reservoirs needed for hatch humidity without spilling water onto electrical parts.

8. Days 19–21: do not help too early

During hatch:

• do not turn the eggs;
• keep vents open as directed by the manual;
• avoid opening the incubator after every first pip;
• allow chicks time to progress and dry.

Frequent opening can rapidly lower humidity when membranes need to remain flexible. A chick may also rest for a long period between the first pip and emergence. Helping too early can cause bleeding if blood vessels have not fully withdrawn.

9. After hatch

Prepare the brooder before hatch day. It should be warm, dry, clean and protected from draughts. Move chicks when they are dry and active while limiting opening time for eggs still hatching.

At the end of the cycle, record:

• total eggs set;
• eggs identified as fertile;
• chicks hatched;
• hatch days and times;
• outages, alarms and lid openings;
• observations from unhatched eggs.

Hatch performance should be considered against fertile eggs, not only total eggs set. This helps separate flock fertility problems from incubator-management problems.

Quick diagnosis

Observation	Possible causes to investigate
Many clear eggs	Flock fertility, long storage, unsuitable egg selection
Early embryo failures	Unstable temperature, contamination, rough handling, egg quality
Hatch much too early or late	Average temperature too high or low, measurement error
Fully formed chicks fail to emerge	Humidity, ventilation, position, frequent opening, temperature variation
Hatch spread over a very long period	Different storage histories, uneven temperature, eggs loaded at different times

These signs guide diagnosis but do not prove one cause. Compare several documented cycles before making major changes.

Frequently asked questions

Must I open the incubator to add water?

Use the external filling port where provided. If opening is necessary, prepare the water and tool first so you can work quickly without splashing electrical components.

What should I do during a power cut?

Keep the lid closed, use only the backup supply intended for the machine and monitor recovery. Read our guide to protecting an incubation cycle during a power outage.

Why does the display differ from my thermometer?

Sensors may sit in different locations and may have calibration offsets. Check the recommended position, compare instruments over enough time and do not apply random corrections.

Should I help a chick out of the shell?

Not automatically. Premature assistance can injure a chick. If a case appears abnormal, seek experienced advice and observe membranes and blood vessels before taking action.

The best setting is one that matches your model, is checked with a reliable instrument and is confirmed by the results of several documented cycles.