Once incubation starts, it takes about 21 days for chicken eggs to hatch. That’s true whether you incubate them mechanically in an incubator or naturally under a broody hen. Both approaches take the same length of time.
Using an Incubator
When I’ve incubated eggs from our flocks in a styrofoam table-top incubator, some eggs will hatch at 21 days, but some eggs will still be hatching on day 22 or even 23. I will normally stop incubating on day 23. Chicks that hatch later than that don’t tend to be as strong or healthy.
Variability in the Time it Takes to Hatch Eggs
Especially with backyard eggs, you will probably seem some variation in when your eggs will hatch. I would expect eggs from large hatcheries to hatch in a narrower time window, closer to the ideal of 21 days.
Because in order to be efficient, large hatcheries cannot have a wide hatch window. They need their eggs to hatch on a single day, maybe within a 12 hour period, so they can ship the chicks. Because the schedule is tight, chicks that are slow to hatch aren’t likely going to be given the opportunity to hatch.
Effectively, large hatcheries are thus selecting for a narrow hatch window. Offspring that are slow to hatch will not become breeders if the hatchery is hatching their own replacement stock. Over time, I would expect that selecting for a narrow hatch window would tend to produce chicks that hatch more closely to the 21 day ideal.
In a home flock, you’re probably not doing this. I’m definitely not, because a narrow hatch window isn’t a priority. Just like you wouldn’t select the tomatoes that you raise in our vegetable garden for ship-ability or long shelf-life, in a backyard flock, you wouldn’t normally select for a narrow hatch window. The other thing to consider is that whatever you aren’t selecting for will likely decline, and you can only select for so many things at once.
The Effect of Temperature
From what I’ve read, incubator temperatures that are too warm can cause your eggs to hatch early, though I’ve not experienced that directly since I keep the temperature within a narrow range.
The incubator that I prefer to use is the GQF 1588, which uses a digital thermostat and has a fan to circulate the air. It keeps the temperature very stable and very close to the target temperature throughout the hatch cycle, with minimal effort. The only time that you might run into difficulty with too high a temperature would be if the ambient temperature in the room was higher than 99º (F).
I’ve also used the GQF 2362E. It takes a little more tweaking during the incubation process. Like the GQF 1588, it has a digital thermostat, but it works differently, and it lacks the digital temperature readout on the top panel. I’ve always used it with a separate digital thermometer and hygrometer placed within the incubator on or near the eggs. As the eggs get closer and closer to hatching, I end up needing to dial down the temperature slightly. I attribute this to the heat that the eggs are increasingly putting off as the chick grows larger inside.
One thing to note on incubator temperature. Even in an incubator with a fan, the temperature differs at different locations in the incubator. The temperature will be warmest initially close to the heating element and slightly cooler nearer on or near the egg tray. But as the eggs develop, they will increasingly put off heat of their own, so the temperature at the egg tray level will increase as hatch day approaches.
Natural Hatching Under a Broody Hen
As mentioned earlier, it takes about 21 days for chicken eggs to hatch underneath a broody hen. The amount of time needed for hatching is essentially the same because an incubator is basically emulating what a broody hen would do when sitting on eggs. It’s providing the right temperature, the right humidity level and it’s turning the eggs periodically.
Which is Better, Natural or Mechanical Incubation?
It depends on what you’re trying to do.
A broody hen (one that is in the mood to set on eggs) can save you a lot of work, and I think the chicks raised by her are smarter and better able to take care of themselves. She keeps them warm. She teaches them to eat. She teaches them how to find food. A good broody hen will even help them learn how to hide from predators. Chicks that are hatched in an incubator then reared in a brooder under artificially produced heat aren’t going to have all this extra training from the hen. So there are some very real benefits to hatching under a broody hen.
That said, broody hens just aren’t all that predictable. At least many of them aren’t. You don’t know exactly when they’ll go broody. They’re more likely to brood during spring, but exactly when they’ll start is unknown. Second, not all broodies will stick with sitting all the way through to the hatch. Third, some of them will hatch your chicks fine, but they won’t take good care of them. And fourth, some broodies eventually get tired of raising chickens and become brutal toward them or toward some of them.
Broody hens ought to be housed separately so they can set and hatch undisturbed by other hens, and so that they can raise their young without the risk of other chickens harming them (which they can and will do at times). So having enough housing available can be a limitation. The housing also needs to be secure enough that animals like skunks cannot dig under it and eat the eggs or the chicks.
If you have a good broody hen, that has the potential to save you some work and raise better-taught chicks for you. But an incubator can work very well and is more predictable.
My Preferred Approach to Incubation and Brooding
My favorite way to incubate is to simultaneously hatch within an incubator and under a broody hen with the same hatch date.
Once a hen starts to go broody, I take away her eggs for a few days. If she’s serious about setting, then she’ll continue to gather eggs under her and incubate them. Meanwhile, I start gathering the eggs that I want to hatch. Typically, I will gather these from my other breeding pairs, which are housed in separate pens from the broody.
When I’m ready to start the hatch, I will place a clutch of eggs under the hen, and I’ll also start a batch of eggs incubating in the incubator. This way, both the hen and the incubator will have the same projected hatch date.
This provides several advantages:
- If the hen ceases to set, I can candle any eggs she still has and I move the good ones into the incubator, so they still have a good chance of hatching. Likely by this time, I will have some empty space in the incubator from having already candled and removed bad eggs from it.
- After chicks hatch in the incubator, I can put some of the baby chicks underneath the mother hen for her to raise, if I want to. As long as I don’t overdo it, and as long as I make this transition at night, there’s a good chance that she’ll accept them and raise them.
What Percentage of Eggs Will Hatch When Incubated?
It varies a lot. My first hatch in an incubator resulted in a fairly low hatch rate. I began experimenting after than and have gotten considerably higher hatch rates.
If you’re setting about 40 eggs in an incubator and only about 50-60% are hatching, there are several things to look at. For one, how is the humidity? Usually, the incubator will come with recommendations for the humidity level. It will differ for chicken eggs versus duck or other types of eggs. I’ve found by experimentation that for me, running the incubator at the low end of the recommended range results in a higher hatch rate.
Temperature is another thing to consider. Are you keeping the incubator close to the target temperature at all times? If it’s in an unheated or un-air-conditioned room, monitor the temperature closely and see if it’s staying on target or not. Variations in the room temperature can greatly affect temperature within the incubator. Remember that small, tabletop incubators don’t have very big heating elements, and they can’t generate a lot of heat, so if the room is cold, they may have difficulty keeping the eggs up to temperature. Conversely, if you place the incubator in a non-air-conditioned spare room during hot weather, the incubator (at least a typical small one) has no way to cool itself, so the temperature inside can go over the target.
Another thing to consider is fertility. Some eggs simply aren’t fertile and won’t develop even if you manage the incubator perfectly. I’ve seen eggs from particular hens never develop. I’ve seen eggs from particular breeding pairs never develop. A rooster can get old and cease to be fertile or cease to fertilize the eggs. One way to diagnose fertility is by candling the eggs and breaking out the ones that don’t develop properly to determine whether there was any development at all. If you label your eggs as to which breeding pair they came from, then you can narrow down and isolate fertility problems. Then try the hen with a different rooster (and vice versa) and see if you get fertile eggs.
You can also check a few eggs from each pen for fertility by breaking them ahead of time and inspecting the yolks. But then that egg is no longer available for incubation. That’s a good approach to use a week or two before incubation so it doesn’t affect the number of eggs you have available to incubate. (See also my article on choosing which eggs to hatch).
Keeping good records of your incubation and hatch will let you tune the process and improve your hatch rate. It’s hard to know what to change if you don’t actually measure and take some notes on what you did. But if you do keep records, then you can make adjustments and improve your hatches fairly quickly so that you’re getting much better hatch rates by the third or fourth hatch. Things I like to track are:
- date and time — write down the date and time of each measurement or note that you add to your logsheets
- temperature — what is the temperature inside the incubator? If possible, you may also want to record the room temperature, particularly if you think it may be somewhat variable.
- humidity — within the incubator. If possible, you may also want to record humidity in the room also, since it affects how quickly you lose moisture from the incubator. I’ve never tracked that, but it seems like a good idea.
- when you add water to the incubator to maintain humidity
- date when you moved the eggs out of the egg rotator trays
- results from candling and breaking out of eggs
- when did the chicks first start to pip (crack the shells)?
- when the first chicks started to hatch, when did most of the chicks hatch, and when did the last chick hatch?
How to Keep Eggs and Chicks Straight
I mark the top of each egg in pencil to indicate the date I collected the egg and which breeding pair (or pen) it was from.
When I move the eggs out of the egg turner on day 18, I place them into homemade mesh drawstring bags. The bags are large enough to hold several eggs each. They also have plenty of room for the chicks to break out of the egg and hatch. I also place a small paper note in the bag to tell which pen the eggs were from. When eggs start hatching, I monitor the incubators closely. This way, I can remove the chicks from the bags and mark them and update my records.
After Hatching in an Incubator
After your chicks hatch, give them some time to dry off in the incubator. Then they will need to be placed in a brooder with get supplemental heat. My preferred way to provide the heat is with a brooder panel, such as the one sold by Premier 1. I do NOT recommend brooding under a heat lamp because of safety reasons. For more information, please see my guide to raising chickens.