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How Fast Do Chickens Grow to Full Size?

When you get your first batch of chicks, you are probably too excited to think about when they are going to start giving you eggs. How long do you need to wait? How fast do chickens grow, anyway? The average length of time for a chicken to get to full size depends on genetics, but the average is 90-100 days for organically raised birds. Is there more to it than that? Yes. Here is what you need to know.

How Fast Does a Chicken Grow to Full Size?

adult chickens

Like people, the growth rate of a chicken is often determined by their bloodline. In other words, some breeds grow faster than others. For example, larger breeds grow more slowly than small breeds. The Cornish Cross, a broiler chicken, reaches full size at 7 weeks old. The immense Jersey Giant breed takes about 18 months!

Here is a look at the specific time it takes for a chicken to be considered full size:

Fast vs Slow Growing Chickens: What Does It Mean?

As you are now aware, chickens have varying growth rates. When shopping around for chicken breeds, you may notice that some are considered “fast-growing” breeds. Others may be called “slow-growing.” What does this mean?

Faster growing chickens are usually hybrids or broilers that were produced to grow and then be used as meat as quickly as possible. They are designed to keep up with the ever-growing demand for chicken meat.

A slower growing chicken, sometimes referred to as heritage breeds, are going to take twice as long to develop when compared to a broiler. You can also think of slow-growing chickens as those predominantly meant for eggs. One example is the Brahma, which is generally not used in industrial meat production because it takes 2 years to reach full size.

Timeline of Chicken Development

In order to better understand how chicks develop into full grown chickens, let’s look at a timeline.

1. Fertilization & Hatching

Once a rooster and hen fertilize the eggs, the process begins. Within 25 hours of fertilization, the egg begins to form. The hen then lays her egg.

chicken hatching eggs

It takes around 21 days for the chick to develop inside the egg. Once the chick is fully developed, it begins to hatch. Eggs must be incubated at the correct temperature in order for development and hatching to begin.


2. The Life of a Chick

During the first few days, a chick remains visibly the same. They will be clustered together under the heat lamp (which is needed for about 4-10 weeks). You may be able to pick out the females from the males right away, if the breed can be auto-sexed. Soon, those little balls of down start to grow. Within 3-6 weeks of hatching, the fluff disappears and real feathers sprout. Combs and wattles also start to develop.

baby chicken in poultry farm

At this point, the chick has either become a pullet or cockerel.

3. Entering Adulthood

Around 16-24 weeks old, the pullet is ready to begin laying eggs. This is the sign when your chick is no longer a baby or teenager but a full-fledged adult. In other words, the pullet is now a hen, and the cockerel is now a rooster. That said, hens and roosters still need time to become full size. Growing up will take a few more months or years, depending on the size and genetics of the chicken in question.

bantam cockerel and a pullet

On average, it takes 12 months for chickens to become full grown.

Want to know more about the life cycle of a chicken? This short video has all the details:

What Factors Affect How Fast a Chicken Grows?

Of course, while genetics play a significant role in the development of an animal, that is not the only thing needed for growth. Chickens can be affected by a number of factors. If you are planning on raising a flock of your own, you need to be aware how such factors can impact your chickens’ growth.


From the time a chick hatches, it needs nourishment. You will need to provide your chicks with a high protein starter for a couple of weeks before swapping over to regular chicken feed. Do not forget that, while feed is essential to the health of your chickens, the occasional treat does wonders too. Do not forget to provide your flock with plenty of clean water, as well.


Did you know that chickens born and raised in lower temperatures tend to eat more and, thus, grow faster? This may come as no surprise. Even humans tend to eat more when the temperature drops. However, this does not mean you should expose your chickens to cold temperatures in hopes of them developing faster. What it means is that you should make them comfortable.

Avoid extreme temperatures — either too hot or cold — and keep your chickens away from excessive humidity. Temperature fluctuations can stress out your chickens, which impacts their overall health.

Breeder & Raiser Practices

chicken big coop

If you want your chickens to grow as healthily and as big as possible, then you need to commit to ethical practices. For instance, keeping the coop and run clean and free of contaminants. Ensuring the coop is well-ventilated and not too stuffy in the summertime. Providing your chickens with quality litter and feed is also crucial to their development.

As mentioned earlier, prioritize keeping your chickens comfortable. Do not overcrowd the coop. Separate sick chickens and get them veterinary care before their disease spreads. So long as you are providing adequate care, as well as food and water, your chickens will grow up as nature intended.

And you will be thanked with loads of eggs.

Final Thoughts on the Growth of Chickens

Even though chickens will continue to grow a little after reaching sexual maturity, most of their development is done around the time the hens begin laying eggs. That said, there are breeds who develop much faster than others. How fast does a chicken grow? Most will reach adulthood in about 18-26 weeks, while some broilers only take 7 weeks to mature and 16 weeks to reach full size!

Knowing this, you can figure out which breeds to use in your flock to ensure you are getting enough eggs, meat, and chicks throughout the year.