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When Are Cats Fully Grown? Here’s What Science Says

Since kittens are literal living balls of fuzzy cuteness, it comes as no surprise most of us do not want to see them get past that stage of their lives. Nonetheless, like any other living creature, your adorable kitten will eventually grow to become the cliché grumpy old cat. But just when does that happen?

Cats grow at different rates, meaning different cats attain full size at different ages. In this article, we’ll discuss everything you need to know about how cats grow.

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Understanding the Stages of a Cat’s Lifecycle

While cats grow at different rates, they go through similar stages in their lifecycles. As such, understanding the general lifecycle of cats can help you determine when your cat is fully grown.

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Image Credit: Albina-Tiplyashina, Shutterstock

Kitten (0–6 Months)

Despite how desperately you want your little one to remain at this stage, cats typically grow past kittenhood at only 6 months of age. However, even though kittenhood marks the shortest stage of a cat’s life, felines grow fastest and change the most during this period.

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Junior (6 Months–2 Years)

This stage is akin to the adolescent years in humans. It marks the transition between kittenhood and adulthood. Most cats attain sexual maturity during the junior phase of their lives, with some reaching their full size by the time they are 2 years old.

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Prime (3–6 Years)

This is when a cat is at its prime as an adult. It has already attained its maximum size and has settled into its life. Expect your cat to be at its healthiest and strongest during this period. While energetic, it is no longer as excitable as it was as a young cat. This age group is equivalent to 28–40 years old in human years.

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Mature Adult (7–10 Years)

This is the transition stage between prime and senior years. In human years, it represents 44 to 56-year olds. Therefore, even though the cat is still relatively healthy during this stage, it starts becoming susceptible to health issues such as diabetes and kidney disease.

Your cat might also begin gaining weight exponentially during this stage due to being less active, as well as its metabolism slowing down. Therefore, you will need to adjust the cat’s diet accordingly.

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Senior (11–16+ Years)

In human years, this age group represents 60 to 80-year olds. As you can imagine, all cats want to do during this stage is rest. This is also when their health takes a turn for the worst, necessitating frequent vet visits.

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Factors Affecting a Cat’s Growth

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Image Credit: Carolyn R, Shutterstock

As mentioned, cats grow at different rates depending on several factors. Those factors include:


As you can imagine, larger cat breeds take a little longer to reach their full size. While the average housecat is typically fully grown by the time it is 2 years old, giant breeds such as the Maine Coon might need up to 4 years to reach their final size. The British Shorthair is another slow-growing cat breed, taking up to 3 years to attain peak adult size.

On the other hand, smaller cat breeds attain full size much earlier, with breeds such as the Siamese cat reaching full growth in as little as 1 year.


As mentioned, cats develop the fastest during the kitten phase, which is why it is crucial to ensure your kitty is getting the nutrition they need to facilitate that growth. Ask your vet to help you curate a diet plan for the young kitty.

Kittens that do not receive sufficient nutrition are at risk of stunted growth, reaching their full size prematurely. This explains why feral cats tend to be smaller than their domestic counterparts.

Health Defects

Some cats have the misfortune of inheriting poor genes, which might cause bone defects or deformities that stunt their growth, such as dwarfism. However, a good diet can go a long way towards lessening the impact of bad genes.

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If you want a definitive answer for when cats attain their peak adult size, we would have to say it is between 2 and 3 years old. Nonetheless, as mentioned, many factors are to be considered when determining when a cat stops growing, with the most important one being the specific breed.

Nevertheless, as long as your kitten is receiving proper care in the way of a nutritious diet, plenty of exercise, and lots of loving, it will attain its full size before you know it. Therefore, try to enjoy every stage of your kitty’s lifecycle, as each phase will pass in what feels like the blink of an eye.

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Featured Image: MirasWonderland, Shutterstock