Incubator Temperature and Humidity for Chicken Eggs

Get exact dates for turning, candling, lockdown, and hatch with the incubation calendar calculator.

What temperature should an incubator be for chicken eggs?

99.5°F (37.5°C) for a forced-air incubator. 101.5°F (38.6°C) for a still-air incubator.

The gap between those two numbers is not a disagreement. It is the whole reason both exist. A forced-air incubator has a fan, so the air inside is one temperature everywhere and you can set the machine to the temperature you actually want the embryo to experience. A still-air incubator has no fan, so warm air pools at the top and cool air settles at the bottom. You set it higher to compensate, and you measure at the top of the eggs, because that is where the embryo sits.

That measurement detail matters more than most people expect. In a still-air machine, a thermometer lying on the floor of the incubator can read 3°F cooler than the air at egg level. Set the machine by that reading and you have quietly incubated the whole clutch cold.

Humidity is the other half, and it is where more backyard hatches fail. Hold 50–55% relative humidity through day 18, then raise to 65–75% for the final three days.

Incubator temperature and humidity chart

Every figure below matches what the incubation calendar computes, so the chart and the calculator will never tell you different things.

Temperature is the same for all eight species: 99.5°F (37.5°C) forced-air, 101.5°F (38.6°C) still-air. That is why it is stated here rather than repeated down every row. What actually changes between species is the calendar and, for geese, the humidity.

Download the chart as a printable PDF — one page, sized for a letter sheet, meant to be taped to the wall above the incubator.

Three things in that table are worth calling out.

Geese are the exception on humidity. They need a noticeably wetter early stage, 60–65% rather than 50–55%. This is not a rounding difference — it comes out of Mississippi State’s own wet-bulb figures for geese, which convert to a genuinely higher relative humidity than the other species in the same table.

Goose and guinea fowl day counts are single picks from a published range. Geese are published at roughly 28–34 days and guinea fowl at 26–28. The chart uses 30 and 27. Treat those two hatch dates as estimates and start watching for pips a few days either side.

Muscovy are not like other ducks. Thirty-five days, not 28, and lockdown starts at day 31. Muscovy are a different species from other domestic ducks, and this catches out people who assume a duck is a duck.

How far off is too far off?

One degree, sustained, is the number to remember.

Mississippi State Extension puts it plainly: minor fluctuations of less than half a degree are tolerated, but do not let the temperature vary more than a total of 1°F. Their framing of the consequences is useful because it is directional rather than vague:

• Consistently too warm produces early hatches, and fewer chicks overall.
• Consistently too cool produces late hatches, and fewer chicks overall.

So if your hatch came off on day 19 or day 23, the calendar itself is a diagnostic. An early hatch is a warm incubator. A late hatch is a cold one. Either way, the total number of chicks drops.

The asymmetry worth internalizing: high temperatures are more dangerous than low ones. A cold incubator slows development and can cause late-term deformities. A hot incubator kills embryos outright, and it does it faster. Half an hour at 105°F will seriously harm or kill a developing embryo. Half an hour at 95°F will not.

Brief excursions are usually recoverable. If the power drops for an hour, or you left the lid off while candling and the temperature sagged, the clutch will very likely be fine. It is the sustained error — the machine that has been running at 98°F for a week because nobody checked — that ruins hatches.

Do not trust the built-in display

This is the single highest-value thing on this page, and it costs about ten dollars to act on.

The temperature readout moulded into the lid of a consumer incubator is frequently off by 1 to 2°F from the air where the eggs actually sit. Given that your entire tolerance is 1°F, an uncalibrated display can consume your whole error budget before you have done anything wrong.

Buy a separate thermometer, put it at egg level, and calibrate it once:

1. Ice water = 32°F (0°C). Fill a glass with crushed ice, add just enough water to fill the gaps, stir, and let it sit two minutes. A correct thermometer reads 32°F.
2. Boiling water = 212°F (100°C) at sea level. Subtract about 1°F per 500 feet of elevation. In Denver, boiling water is roughly 202°F.
3. Note the offset and apply it. If your thermometer reads 33.5°F in ice water, it runs 1.5°F hot, and your true incubator temperature is 1.5°F below what you see.

Mississippi State suggests a simpler field version — hold your incubator thermometer next to a clinical or laboratory thermometer under lukewarm tap water and compare. That works, and it is better than nothing, but the two-point ice-and-boiling method tells you whether the error is constant across the range, which a single lukewarm reading cannot.

One more from the same source, for anyone using an older glass thermometer: a thermometer with a split or gapped mercury column will not read accurately. Discard it rather than trying to work around it.

Humidity: the part that is genuinely contested

Here is something most pages will not tell you. The published early-stage humidity figure for chicken eggs is not settled, and the spread is wide enough to matter.

Extension publications express humidity in wet-bulb degrees F, not relative humidity, because that is what the incubator industry has historically used. Mississippi State publishes this conversion:

Now run the numbers. Their species table lists chicken eggs at 85–87°F wet-bulb at a 100°F dry bulb. Convert that with their own chart and you get roughly 55–60% relative humidity — not the 50–55% that circulates as the standard backyard figure. Elsewhere in the same document their prose recommends 58–60%.

So the honest range across published guidance is about 50% to 60%, and anyone quoting a single number to two significant figures is overstating what the sources actually support.

FlockMath uses 50–55% as its operating figure, at the drier end of that band, because most backyard failures are wet-side failures rather than dry-side ones. But if you are hatching in a genuinely arid climate, the higher end of the published range is not a mistake — it is the other half of the same evidence.

What actually governs humidity

The reason the range can be that wide and hatches still succeed is that relative humidity is a means, not the target. The target is moisture loss.

Mississippi State gives the real criterion: the egg must lose about 12% of its weight across incubation for a good hatch. Humidity is simply the lever you pull to land there. Two keepers running 50% and 60% in different climates can both hit 12% weight loss, and both will hatch well.

This reframes the whole problem, and it gives you two ways to check your work instead of trusting a hygrometer:

• Weigh the eggs. Weigh the clutch on day 1 and again at each candling. You are looking for a steady march toward about 12% down by day 18. Too little loss means raise the humidity; too much means lower it.
• Candle the air cell. The air cell at the blunt end grows as moisture leaves. By day 7 it is a small dome, by day 14 clearly larger, and by day 18 it should occupy roughly a third of the egg. An air cell that is too small on day 18 means the egg has been too wet.

The air cell method needs no equipment beyond a flashlight and is the one most backyard keepers will actually do.

Dry incubation, and when it is the wrong choice

“Dry incubation” means running the first 18 days with the water reservoir empty, topping up only if humidity falls below about 40%, then flooding at lockdown. It has become the default advice in backyard circles, and in temperate climates it works well.

It is not universal advice, though, and the reason is simply that ambient humidity varies enormously:

• Arid climates — Arizona, Nevada, inland Australia, high desert. Ambient humidity can sit under 20%. Dry incubation here is not dry incubation, it is desiccation. You will need supplemental water from early on.
• Wet climates — the Pacific Northwest, the UK in winter, coastal subtropics. Ambient can already exceed 55% before you add anything. Here the standard “fill the reservoir” advice overshoots, and dry incubation may still be too wet.

Do not adopt a humidity strategy because it worked for someone on a forum. Adopt the strategy, then verify it against your own air cells or egg weights and adjust. That feedback loop is what actually produces a hatch.

Lockdown: 65–75% and hands off

For chickens, lockdown is days 19, 20, and 21. Three things change:

1. Stop turning. By day 18 the chick is orienting to hatch — internal pip into the air cell, then external pip through the shell. Turning disorients it.
2. Raise humidity to 65–75%. The membrane has to stay pliable so the chick can cut a clean circle around the shell.
3. Stop opening the incubator. This is the one people break.

Every time the lid comes off during lockdown, humidity crashes and takes five to ten minutes to recover. A chick that has pipped is sitting in a shell with a membrane exposed to that air. Dry it out and it shrink-wraps: the membrane tightens against the chick, it cannot turn to cut, and it dies in a shell it had already broken.

You will hear peeping and want to look. This is the single most common cause of a stuck chick, and the fix is entirely psychological. Leave it shut.

For what is happening inside the egg on each of the 21 days — and which days you turn, candle and lock down — see the day-by-day incubation chart.

What wrong humidity looks like

The pattern worth learning: early-stage humidity errors show up as a wrongly sized air cell. Lockdown humidity errors show up as a chick that pipped and then failed. Those are different problems with different fixes, and telling them apart tells you which end of your process to change.

Frequently asked questions

What temperature should an incubator be for chicken eggs?

99.5°F (37.5°C) in a forced-air incubator, or 101.5°F (38.6°C) in a still-air incubator measured at the top of the eggs. Stay within about 1°F. Published extension figures for forced-air run between 99 and 100°F depending on species and source.

What humidity do chicken eggs need in an incubator?

50–55% relative humidity from day 1 to day 18, then 65–75% for lockdown on days 19–21. Published early-stage guidance spans roughly 50 to 60%, so treat your climate and your egg weight loss as the deciding factors rather than a single number.

Why is still-air set higher than forced-air?

A still-air incubator has no fan, so warm air layers at the top and cool air settles at the bottom. The higher setting compensates for that gradient. It only works if you measure at the top of the eggs, where the embryo actually is.

Is it better to run humidity too high or too low?

Slightly low is generally safer than slightly high during days 1–18, because a too-wet egg leaves the chick no air space to pip into. During lockdown the opposite is true — too low causes shrink-wrapping, and that is the most common late-stage killer.

How do I know if my humidity is right without trusting the hygrometer?

Candle the air cell. It should be a small dome at day 7, clearly larger at day 14, and about a third of the egg at day 18. Or weigh the eggs — a clutch should lose roughly 12% of its starting weight by day 18.

Does one degree really matter?

Yes, sustained. Brief excursions during candling or a short power cut are usually survivable. A machine running a degree off for a week is not — it shifts the hatch date and cuts the number of chicks that make it.

What temperature and humidity do duck or quail eggs need?

The same temperature as chickens — 99.5°F forced-air. Humidity is also the same at 50–55% early, except geese, which need 60–65%. What changes by species is the calendar: quail hatch at 17 days, ducks at 28, Muscovy at 35. The chart above covers all eight.

Sources

• Mississippi State University Extension — poultry incubation guide (PDF): the per-species incubation table (days, temperature, wet-bulb humidity, stop-turning day), the wet-bulb to relative-humidity conversion table reproduced above, the 1°F tolerance and its early/late hatch consequences, the 12% egg weight loss criterion, and the thermometer-accuracy warning. Every stop-turning day in the chart above matches this table.
• Mississippi State University Extension — Incubation duration periods: incubation length by species.
• Oklahoma State University Extension — Artificial Incubation: forced-air versus still-air temperature, including the roughly 2–3°F still-air adjustment.
• Texas A&M AgriLife Extension — E-635, Hatching Eggs in the Classroom (PDF): temperature, humidity, turning, and candling practice.

Some figures here are Flockmath’s own choices rather than a single published number. The site-wide 99.5°F forced-air figure sits inside the 99–100°F range published per species; 50–55% early humidity sits at the dry end of the 50–60% published spread, for the reasons given above; and the goose day-count of 30 and guinea fowl 27 are single picks from published ranges of 28–34 and 26–28. Candling schedules for the non-chicken species are our own spacing rather than published dates.

Figures are planning guidance for backyard incubation, not veterinary advice. For flock health concerns, consult a licensed poultry veterinarian. Last reviewed August 2026.