Incubator Humidity for Chicken Eggs, Week by Week
TL;DR: 50–55% for days 1–18, then 65–75% for lockdown (days 19–21). Humidity is really a control on how much water the egg loses through the shell — that loss creates the air cell the chick breathes from before it pips. Too little loss drowns the chick; too much dries it onto the membrane. In a humid Philippine room the usual problem is too much humidity, not too little, and that is harder to fix because adding water is easy and removing it is not. Candling the air cell is how you find out which way you are wrong.
Temperature gets all the attention. Humidity is what quietly decides how many chicks make it out of the shell.
What Humidity Is Really Doing
An eggshell is porous. Across the 21 days the egg loses water vapour through it, and the space left behind becomes the air cell at the blunt end.
That air cell is not incidental — it is what the chick breathes from when it internally pips, in the hours before it breaks through the shell. Get the water loss wrong in either direction and the chick meets a problem it cannot solve:
| Water loss | Air cell | What happens |
|---|---|---|
| Too little (humidity too high) | Too small | Chick has too little air space and too much fluid; commonly drowns at internal pip |
| Correct | Grows steadily | Chick has air to breathe while it works out |
| Too much (humidity too low) | Too large | Chick is dehydrated, membrane dries and toughens, chick sticks and cannot turn |
So “what humidity should I run” is really the question “how fast should this egg lose water,” and the answer is: steadily, across three weeks.
The Targets
| Phase | Days | Humidity |
|---|---|---|
| Development | 1–18 | ~50–55% |
| Lockdown | 19–21 | 65–75% |
The lockdown jump matters because the membrane the chick has to cut through must stay soft. A membrane that dries out becomes leathery, and a chick that has pipped and cannot progress is usually fighting exactly that. Full detail in lockdown at day 18.
The Philippine Problem: Too Wet, Not Too Dry
Most incubation advice is written for temperate climates where the fight is to raise humidity. Here it is often the reverse.
An incubator in a humid room, especially in the wet season, can sit above the target with no water in the channels at all. And humidity is asymmetric to control:
- Raising it is easy — more water surface area. Add water to more channels, or add a damp sponge.
- Lowering it is hard — you need ventilation and airflow, or less water surface. Some units have adjustable vent plugs; open them.
Practical steps when you are running too wet:
- Empty some or all of the water channels. Yes, all — if the room supplies enough.
- Open the vents.
- Move the incubator to a drier room if you have one, away from the kitchen and the bathroom.
- Watch the air cell at candling rather than the hygrometer alone. It is the reading that cannot lie.
Candling Tells You What the Hygrometer Cannot
Your hygrometer might be wrong. The air cell is direct evidence.
Candle at day 7, 14 and 18 and look at the air cell at the blunt end. It should be visibly larger each time. Compare against the images and method in our candling eggs guide.
- Air cell barely growing → too little water loss → lower the humidity.
- Air cell growing too fast, unusually large by day 14 → too much water loss → raise the humidity.
- Growing steadily → leave everything alone.
Adjust between hatches based on what you saw, and write it down. Two or three batches of notes will tell you more about your machine and your room than any general figure.
Verify the Hygrometer
Same discipline as the thermometer in our incubator temperature guide.
- Run the machine empty for 24 hours before setting eggs.
- Compare the built-in display against a separate hygrometer placed at egg level.
- Trust the separate instrument if they disagree.
- Remember that budget humidity sensors are generally less accurate than their temperature sensors, and they drift with age.
Practical Handling
- Use warm water to top up channels so you do not drop the temperature at the same time.
- Top up quickly, with everything ready before you open the lid.
- Surface area matters more than volume. A wide shallow channel raises humidity more than a deep narrow one holding the same water.
- Never open during lockdown unless something is genuinely wrong. This is the single most common self-inflicted hatch failure — a keeper checking on the chicks, humidity crashing, membranes drying.
Reading a Failed Hatch
| What you found | Commonly associated with |
|---|---|
| Chicks fully formed, dead in shell, not pipped, wet | Humidity too high; air cell too small |
| Chicks pipped then died, stuck to a dry tough membrane | Humidity too low at lockdown, or the incubator was opened |
| Chicks hatched early and small | Temperature high — see incubator temperature |
| Hatch spread over several days | Temperature swinging, or eggs set at different times |
Fuller version in why eggs did not hatch.
The Honest Limits Here
The humidity ranges here are standard incubation figures consistent with our main incubation guide, and the air-cell mechanism is well documented. What this guide deliberately does not give is a weight-loss percentage target — measuring egg weight loss across incubation is a real technique used by serious hatchers, but it needs accurate scales and careful record-keeping, and quoting a number without that method attached would mislead more than it helps. Follow your incubator’s own manual where it specifies settings for that model, and let candling be the final check.
Related: incubator temperature, lockdown at day 18, candling eggs, why eggs did not hatch.
Frequently Asked Questions
What humidity do chicken eggs need in an incubator?
Roughly 50-55% relative humidity for days 1-18, raised to 65-75% for lockdown on days 19-21. The lockdown increase keeps the internal membrane soft enough for the chick to pip through.
What does humidity actually control?
How fast the egg loses water through its shell over the 21 days. That gradual loss forms the air cell the chick breathes from before it pips. Too little loss and the chick has no air space and drowns; too much and it dries out and sticks to the membrane.
How do I know if my humidity is right?
Candle the eggs and watch the air cell. It should grow steadily across the 21 days. An air cell that stays small means humidity is too high; one that grows too fast means it is too low.
Why is humidity harder to control in the Philippines?
Because ambient humidity is already high, so an incubator sitting in a humid room may exceed the target with no water added at all. Lowering humidity is harder than raising it — you can always add water, but removing moisture needs ventilation.
What if chicks pip but die before hatching?
That pattern is commonly associated with humidity problems at lockdown — most often a membrane that dried and hardened because the incubator was opened, or because lockdown humidity was too low.
Do I need to add water every day?
You top up the water channels as needed to hold the target reading. How often depends on your machine and your room. Watch the hygrometer, not the calendar.
Should I trust the incubators humidity display?
Verify it against a separate hygrometer before setting eggs, the same way you verify the thermometer. Humidity sensors are the less accurate of the two in most budget machines.