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Home > Cats > When Does My Kitten Become an Adult Cat? Vet Reviewed Facts & FAQ

When Does My Kitten Become an Adult Cat? Vet Reviewed Facts & FAQ

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Reviewed & Fact-Checked By

Dr. Lauren Demos

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

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Getting a new kitten is an exciting time, but if you already own a cat, you understand how short-lived that time may seem. It can sometimes feel like your kitten has reached its next milestone in the blink of an eye, and it’s suddenly not a kitten anymore.

Kittens develop fast; by 12 months, you will have an adult cat on your hands. Your cat may still carry some mischievous, kitten-like qualities, but generally, by that time, they have calmed down, grown bigger, and their needs have changed.

Looking after a kitten may present challenges, but it becomes easier as they grow up. However, it’s important to understand the timeline of their development so that you can raise a happy and healthy cat.


Kitten Development Stages

Kittens grow quickly, which makes the change seem seamless, but several changes occur while becoming an adult. By understanding and taking notice of these developmental changes, you can determine when your kitten has reached or is close to reaching the adulthood milestone.

cute adorable funny munchkin kitten
Image By: MDavidova, Shutterstock

1–2 weeks: Toward the end of their second week, most kittens would have opened their eyes for the first time. They will be nourished by their mother’s milk, gaining about 10-30 grams a day.

4 weeks: At 4 weeks or one month old, your kitten will start getting curious and eager to explore. This is also when they begin to become a little playful. Their milk teeth will start appearing, and they can start eating a bit of solid food.

10–12 weeks: Kittens are much more independent around this time, so they can now be separated from their mother. Your kitten will also be ready for its first vaccine.

4 months: At 4 months, the milk teeth will begin to fall out and be replaced by adult teeth. Growing adult teeth should be complete by 6–7 months.

6 months: This is the halfway mark. You will notice your kitten has grown a lot bigger, and it won’t get much larger as it continues to develop. Your kitten is also maturing sexually and will begin heat cycles and mating behavior. This is an excellent time to have your kitten at, or before.

12 months: Your kitten is now just reaching early adulthood. They have typically reached their full size and are fully socialized.


Factors that Influence a Kittens Growth Rate

Many factors will determine how fast a kitten will reach adulthood, which is why the growth rate in some cats and other breeds may seem different.


The growth rate of a cat can be affected by its breed. Naturally, larger breeds will take longer to reach their full size. Maine Coon’s, one of the largest breeds of cats, can take up to 4 years to reach their full size. Knowing your cat’s breed will help you determine when it has reached adulthood.


A kitten’s diet will significantly affect its development. If they are fed a protein-rich, high-quality diet, they will have a natural growth rate. Kittens that do not receive a proper diet may have slow or stunted growth.


The age at which a kitten is spayed or neutered will also influence its growth rate. Once a kitten has been fixed, its appetite may increase.

kitten eating
Image By: MaraZe, Shutterstock

When Exactly Do Cats Reach Their Full Size?

The first week of a kitten’s life is when it grows the fastest. They usually double their size in the first week and will continue to grow about an ounce every 3 days.

Most experts agree that a cat will reach its full size or adulthood at 12 months old. Even though most cats stop growing at 12 months, some can reach full size at any age between 18 months and 4 years, but it will be at a slower rate.

How Will My Cat Change Once It’s an Adult?

We know that our kittens will generally reach adulthood at about 1 year of age, but some behavioral and physical changes will take place, which will indicate that your kitten is reaching maturity.

  • If you have more than one cat in the house, you will begin to notice your cat fighting for alpha status. Your cat may growl, hiss, and swipe its feline roommate in a battle to establish their hierarchy. This is all very normal, so just be patient with the process.
  • Your cat’s coat may lighten or change color.
  • Your cat loses its baby teeth.
  • Your cat will be more independent.

The best way to know when your cat has stopped growing and is reaching adulthood is to weigh and measure it every month. You will eventually notice that the measurements only increase slightly until they stop changing.


You must transition your cat from kitten food to adult food; however, the right time depends on many factors. Generally, the appropriate transition age is 10–12 months. It is recommended to slowly transition your cat from kitten food to adult food by gradually introducing it over 5–7 days. It is best to get advice from your veterinarian as your vet can recommend a suitable adult food and ensure you are meeting your cat’s nutritional needs.

At about 14 months, it is recommended that your cat receives a booster vaccination to maintain immunity from disease. This is also a good time for deworming and flea medication to protect your cat from parasites.

Now that your cat is bigger and its muscles have developed, your adult cat will need regular exercise to stay healthy and fit. This will keep your cat’s mind active, but just because it is now an adult doesn’t mean it won’t enjoy its toys. Keep your cat mentally and physically healthy by keeping its favorite toys around.

If your cat is not fixed, it’s time to consult your vet about your cat being neutered or spayed. If you are uncertain, your vet will happily discuss the benefits.

fluffy white cat walking on tree stumps outside
Image By: Alyona Bogomolova, Unsplash

How to Keep Your Kitten Healthy

For your cat to grow into a healthy adult and reach its suitable size, it is crucial to keep your kitten healthy. Here are some essential tips you can follow:

  • Ensure your kitten is fed a well-balanced diet and high-quality kitten food.
  • Get your kitten vaccinated and follow your vet’s recommended schedule.
  • Treat your kitten for internal parasites.
  • Provide a quiet and comfortable place for your kitten to sleep. On that note, never wake a sleeping kitten!
  • Make time to play and bond with your kitten.
  • Learn your kitten’s body language. This will help you pick up signs that your cat may be ill.
  • Consider getting your kitten spayed or neutered.



A kitten is said to reach its full size by 12 months old when it is considered an adult. However, their growth rate can depend on many factors, such as their breed, diet, and if they have been fixed. It is vital to know your kitten’s growth cycle and recognize when changes are taking place so that you can provide your cat with the best and appropriate care. The first year of your kitten’s life will pass by rapidly, and even though it may seem challenging, make sure you take it all in and enjoy the short period of adorable kittenhood.

Featured Image Credit: Lux Blue, Shutterstock

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