Once a hen goes broody and starts setting on eggs, it takes about 21 days for the eggs to hatch, which is the same amount of time it would take in an egg incubator.

When it comes to eggs that your home flock is laying, there is some variability in how long it takes, so don’t be surprised if it takes 22 or 23 days for some of the eggs to hatch.

If your hen has just begun to set

What I recommend in this case is to remove the early eggs that she’s sitting on every day for a few days.

This will accomplish two things:

• One, if she isn’t serious about setting, then she’ll get annoyed with you and stop setting.
• Second, it gives you a chance to gather the eggs that you want hatched and place those under her. Those might not be the same eggs as the ones she chose.

I go into more detail on hatching in an article on hatching chicken eggs under a broody hen.

If you are using an incubator instead of a broody hen

When I’ve incubated eggs from our flocks 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 hatch time

Especially with backyard eggs, you will probably seem some variability 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.

This is because, in order to be efficient, large hatcheries need a narrow 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.

The result?

Effectively, large hatcheries are thus selectively breeding 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 your 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.

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.

What percentage of eggs will hatch?

It depends, but if things go well, and if all the eggs are fertile, you can expect around 70-80% of them to hatch.