Hatching Eggs in an Incubator: Temperature and Timing

Author: Elliott Garber, DVM

Chicken eggs hatch in 21 days, and a good incubator hatch comes down to holding three things steady: temperature at about 99.5 to 100 degrees Fahrenheit in a forced-air incubator, humidity around 50 to 55 percent for the first 18 days, and turning the eggs several times a day until day 18. On day 18 you stop turning, raise the humidity to roughly 65 to 70 percent, and close the lid for good. That last stretch is called lockdown, and the single most important rule of the whole process is that you do not open the incubator during it.

Whether you are hatching from your own flock or eggs someone sent you, the mechanics are the same. What changes your odds is how fresh and how well handled the eggs were before they ever reached the incubator, and how disciplined you are about leaving the machine alone at the end. If you are new to chickens generally, the chicken species page is a good hub, and this guide pairs naturally with the broody-hen guide for people weighing whether to let a hen do the job instead.

Sourcing and settling the eggs before you set them

The best hatch starts before the incubator is even plugged in. Fertility and freshness matter more than any dial you will turn.

If you are collecting from your own flock, you need a rooster with the hens, and you want eggs that are clean, uncracked, and normally shaped. Gather them promptly and store them somewhere cool. Mississippi State University Extension recommends holding hatching eggs at 50 to 65 degrees Fahrenheit with around 70 percent humidity, pointed (small) end down, and tilting or repositioning them once a day so the yolk does not settle against the shell. Hatchability holds up well for about a week; after that it drops off, and the practical outer limit for chickens is around three weeks. Fresher is always better, so set them as soon as you have a full clutch.

Do not wash hatching eggs. The shell has a natural coating (the bloom) that helps keep bacteria out, and scrubbing removes it. If an egg is only lightly soiled, leave it; if it is heavily dirtied, it is a poor hatching candidate anyway.

Shipped eggs are a different animal. Being tossed around in transit scrambles the air cells and generally lowers hatch rates compared to eggs from your own coop, so temper your expectations. The single most useful thing you can do with a box of shipped eggs is let them rest. Unpack them, set them pointed end down in a carton, and let them sit undisturbed at cool room temperature for a full 24 hours before setting them. This lets the jostled air cells settle back into place. Only after that rest do they go into the incubator.

Set up and run your incubator empty for a day before eggs go in, too. You want to confirm it holds a steady temperature and humidity in the spot where it actually lives (away from windows, heat vents, and drafts) before you trust it with a clutch. A separate, calibrated thermometer and hygrometer are worth the small cost, because a machine’s built-in readout can be off by several degrees.

Temperature: the number you cannot get wrong

Temperature is the variable with the least room for error. For a forced-air incubator (one with a fan circulating the air), hold it at about 99.5 to 100 degrees Fahrenheit for the entire run. That fan keeps the air uniform, so a single reading anywhere in the chamber is representative.

Still-air incubators (no fan) are trickier, because warm air rises and layers. Heat pools near the top and is cooler down low, so the reading depends entirely on where you measure. For a still-air machine, run a slightly higher air temperature and, critically, measure it at the height of the top of the eggs, not at the floor of the incubator or up near the lid. That is the level the embryos actually experience.

Small, brief swings are survivable, but sustained error is not. Run consistently too hot and you rush development, producing early, weak, or deformed chicks; run too cool and you delay the hatch and lower the number that make it. If your house has big temperature swings or the power flickers, put the incubator in the most climate-stable room you have. When in doubt, trust a separate calibrated thermometer over the machine’s display.

Humidity: two different targets

Humidity works in two phases, and mixing them up is one of the most common reasons a hatch fails.

For roughly the first 18 days, aim for about 50 to 55 percent relative humidity. This lets the egg lose the right amount of moisture over time so the air cell inside grows to the correct size, which the chick needs for the final days. Some extension guidance runs a bit higher, in the 58 to 60 percent range, and the honest truth is that the ideal depends on your local climate and your specific machine. The way to check whether you are in the right zone is candling: the air cell should be growing steadily as the days pass. If it is too small, run drier; too large, run a little wetter.

Then, at lockdown on day 18, you raise humidity to about 65 to 70 percent and hold it there through hatch. The higher moisture keeps the inner membrane soft and pliable so the chick can turn inside the shell and break free. This is exactly why you top up the water reservoirs right before you close the lid on day 18, so you will not need to open it again.

Turning: keep it moving until lockdown

For the first 17 days, the eggs need to be turned. Turning stops the developing embryo from sticking to the shell membrane and helps it develop evenly. Extension guidance is to turn at least four to six times a day, and turning three to five times daily is a solid, common target for a backyard hatch. Use an odd number of turns per day (three or five, not four) so the eggs do not spend every single night resting on the same side.

If you turn by hand, wash your hands first, mark one side of each egg with a soft pencil “X” and the other with an “O” so you can see at a glance that every egg got flipped, and turn them gently by rocking them 180 degrees. Every time you open the incubator you lose heat and humidity, so be quick and purposeful.

An automatic turner takes this chore off your hands entirely. It sits in the incubator and slowly rocks the eggs on a schedule, which means fewer lid openings, steadier temperature and humidity, and no forgotten turns. It is the single upgrade that most improves a beginner’s hatch, and it frees you to leave the machine closed. Whatever method you use, the rule is the same: turn regularly through day 17, then stop.

Candling: check development around day 7 and day 14

Candling means shining a bright, focused light against the egg in a dark room so you can see inside the shell. It lets you separate the eggs that are developing from the ones that are not, so you can pull the duds before they spoil.

Around day 7 a developing embryo shows up as a small dark spot with thin blood vessels radiating out from it, often described as looking like a spider on the yolk. An egg that is completely clear with no veins at day 7 is almost certainly infertile or never started developing; these are called “clears.” Around day 14 a healthy embryo has grown enough to fill much of the shell as a dark mass, with a clear air cell at the fat end. An egg that looked alive earlier but now shows a blood ring or has gone dark and still is a “quitter,” an embryo that started and then died.

Remove clears and quitters at these checks. Beyond freeing incubator space, there is a real safety reason: a dead egg can rot, build up gas, and eventually explode inside the incubator, coating your viable eggs in bacteria and ruining the hatch. When you are unsure whether an egg is alive, it is generally safer to leave it until the next candling than to toss a slow developer, but a clear blood ring or an egg that smells off should come out.

Keep candling quick and gentle, out of direct sun, and get the eggs back into the warm incubator promptly. Do not candle during lockdown.

Lockdown: hands off, day 18 to hatch

Lockdown is the last three days, and it has one governing rule: leave the incubator closed. On day 18 you do your final tasks all at once. Stop the turner (or take the eggs off the turner and lay them on the incubator floor), top up the water to bring humidity to about 65 to 70 percent, confirm the temperature is steady, and then shut the lid and walk away.

From here you watch through the window, not by opening the door. Around day 21 you will see a chick “pip,” making its first small hole in the shell, and then over many hours it slowly “zips” its way around the shell and pushes out. This is slow, and it looks alarming. A chick can rest for a long time between bursts of effort. That is normal, and it is not your cue to intervene.

The reason the closed-lid rule is so strict is physical. When you open the incubator during hatch, the warm humid air rushes out and the humidity crashes in a minute or two. That sudden drop can dry and tighten the membrane around a chick that has already pipped, effectively shrink-wrapping it so it cannot turn or break free. Mississippi State University Extension notes that this dried, shrunken membrane is usually caused by low humidity during hatching, and that it can happen within a minute or two of opening the incubator to fuss with other chicks. So you keep it closed during hatching. Let the early hatchers dry off and fluff up inside; they are fine in there for a day or so on the yolk they absorbed, and you gather everyone once the hatch is done.

On “helping” a hatch

Resist the strong urge to help a struggling chick out of its shell. A hatch takes many hours by design, and a chick that is still absorbing the last of its yolk sac and blood supply from the shell membrane is not ready to come out. Break the shell for it too early and you can rupture those vessels and cause fatal bleeding, or free a chick that is not strong enough to survive.

Assisting a hatch is genuinely a last resort, attempted only when a chick has clearly pipped, then gone a very long time (well past a day) with no progress and signs of real distress, and even then only by a keeper who knows how to check for absorbed blood vessels and can keep the humidity up while doing it. For most people, most of the time, the right and hardest thing to do is nothing. Chickens have hatched themselves without us for a very long time.

After the hatch: dry, then move to the brooder

Leave newly hatched chicks in the incubator until they are dry and fluffy, which keeps that high humidity intact for eggs still working. Once the hatch has clearly finished and the chicks are dry, move them to a warm, clean brooder with water and chick starter. From there, the raising baby chicks guide covers brooder temperature, feed, and the first weeks.

This is also the natural moment to start records. Adding each chick (or the hatch group) to Creatures gives you a place to track hatch date, parentage, and any health notes as they grow. See how to add an animal, how to add a record, and how reminders and upcoming care work so vaccination or health checks do not slip. Still deciding on names for the new arrivals? The chicken name generator is a fun place to start.

Frequently asked questions

How many days do chicken eggs take to hatch?

Chicken eggs hatch in about 21 days from the day you set them. Some hatch a little early and some a little late depending on how steady the temperature ran, but 21 days is the standard. Other poultry differ: ducks and most large-breed eggs take longer, so do not go by a chicken timeline for a mixed hatch.

What temperature and humidity should I run?

For a forced-air incubator, hold about 99.5 to 100 degrees Fahrenheit the whole time, with humidity around 50 to 55 percent for days 1 to 18, then raised to about 65 to 70 percent for lockdown. A still-air incubator runs slightly warmer, measured at the top of the eggs. Trust a separate calibrated thermometer over the machine’s own display.

Do I really have to stop turning at day 18?

Yes. By day 18 the chick is getting into hatching position, and continued turning or an open lid at that stage does more harm than good. Stop turning, raise the humidity, and leave the incubator closed until the hatch is complete.

Why are my shipped eggs hatching poorly?

Shipping is rough on eggs. The jostling damages air cells and generally lowers hatch rates compared to eggs from your own flock, even when everything else is done right. Letting shipped eggs rest pointed end down for 24 hours before setting them gives you the best shot, but a lower hatch rate from shipped eggs is common and not necessarily a mistake on your end.

Should I help a chick that is struggling to hatch?

Almost never. Hatching is slow and looks harder than it is, and a chick that is still absorbing its yolk and blood supply is not ready to come out. Helping too early can cause fatal bleeding. Intervene only as a genuine last resort, long after a pip with no progress and clear distress, and ideally with guidance from someone experienced.

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