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Kittens to 18 Months, When do Cats Stop Growing?

Whether you’re an experienced cat parent or just adopted your first kitten, one of the questions that may cross your mind is when do cats stop growing?

It’s not as simple as human children who generally reach their full size by 21. There’s no universal answer for when your little fluff ball will reach maturity. But there are some pretty good insights from experts about what to expect as your cat goes from kittenhood to adulthood.

So, when do cats actually stop growing?

Veterinarians and experts report that cats are likely to stop growing when they’re approximately one year old. For the average cat, about 95% of their growth is complete at this point.

Dr. Lauren Demos, BVMS, American veterinarian board-certified Feline Practitioner and Chief Veterinary Officer at Pettable, has valuable insight on this. In their first six months, Demos says that kittens grow “exponentially.” In these crucial early months, kittens began to gain weight, lean muscle mass, and build up strong bones.

What factors affect my cat’s growth?

There are four major factors that can affect your cat’s growth:

  1. Genetics, including breed
  2. Nutrition
  3. Health conditions and disorders
  4. Their sex and when they’re spayed or neutered

How big should my cat be?

How big your cat “should” be varies from feline to feline. Many factors contribute to the size your kitty reaches in adulthood.

On average, veterinarians tend to agree that the ideal weight for the average adult cat is 10 pounds.

That is the average cat, mind you. This number doesn’t take into consideration our feline friends who are on the heftier size.

Genetics play a huge role in how big your kitten can grow in their adulthood. The largest cat breeds like stockily-built Maine Coons and Norweigan Forest Cats could easily tip the scales at 20 pounds. They also tend to grow for longer periods, with Maine Coon cats growing until they’re 4 years old.

If your cat has a broad frame, and significant muscle mass like one of these larger breeds, then how big they grow could exceed the average.

Sex is also something to take into consideration. Across the board, male cats generally tend to be larger than female cats. Dr. Lauren Demos puts those numbers at 10 – 15% larger.

The best way to find out how big your cat should be is to consult your veterinarian or another expert in feline health and medicine. A full exam is the best way to gauge where your cat is in terms of a healthy size and weight.

when do cats stop growing small siamese kitten

Why is my cat so small?

If you’re concerned about having a cat that’s too small, the first place to start is how old they are.

Healthy kittens grow rapidly in their first six months.

If your kitten is at a particularly early stage in their life, they can be very small. It’s normal for kittens to weigh as little as 2 lbs when they’re 8 weeks (or 2 months) old.

My kitten isn’t growing

What if your kitten is growing at a much slower rate than expected? If you notice that your kitten isn’t growing at all as the weeks go by, it’s time for a trip to the vet.

Poor nutrition and improper diet is a huge factor in your kitten’s growth. Kittens who aren’t consuming enough calories or eating balanced, nutritionally complete foods could become malnourished. As a result they could suffer slow or stunted growth.

Genetics also plays a role here. Your cat may be full or part Singapura, Abyssinian, Cornish Rex, or Siamese. These naturally petite felines stay small. They can weigh as little as five pounds when they reach adulthood.

There are also some health conditions that your cat may have inherited from their biological feline family.

Conditions that stunt growth in cats

If you’re concerned about your kitten’s growth or worried that they may have one of the conditions below, do not wait to see your vet. Some of these conditions require immediate care.

Internal parasites

Tapeworms, also known as Dipylidium caninum, are known for causing digestive upset in cats and stunting growth in kittens.

Feline Leukemia

Also known as FeLV, this virus often causes stunted or very slow growth in kittens. FeLV depletes your kitten’s appetite, depriving kittens of the nutrients they need to grow and forcing their organs to work overtime.

Dwarfism

Feline dwarfism is a mutation that causes abnormally small proportions and stunted growth. There’s a lot we don’t know about this rare and complex genetic defect.

Bone deformities or disorders

Known as osteochondrodysplasia, this condition causes abnormally short bones, a large head, and poor or very little growth.

when do cats stop growing kitten

What happens in the early weeks and months of your kitten’s growth?

You should expect to see very noticeable growth in your kitten as the weeks and months pass. If you’re a visual learner, Alley Cat Allies put together a chart that shows pictures of every stage of kitten growth and development.

To give you a sense of the gravity of your kitty’s growth, by the time your kitten hits their first birthday, they could be twenty times larger than they were at birth.

Feline growth markers

Beyond gaining weight and growing longer, your kitten is also developing in other physical and biological ways. Here are some feline growth markers to look out for:

Newborn kittens to 1 month

  • Newborns: kittens weigh about 3.5 ounces, eyes and ears are shut
  • Week one: kittens weigh 7 ounces, their weight has doubled since birth
  • Week 2: kittens weigh 8 – 12 ounces, eyes are fully open
  • Week 3: kittens weigh 12 – 15 ounces, teeth begin emerging
  • Week 4: kittens weigh 12 – 15 ounces, can walk, run, and play

Kittens 3 to 12 months

  • Three months: kittens weigh 2 – 4 pounds, can eat solid food, and all teeth have emerged
  • Six months: kittens weigh about 6 pounds, reach sexual maturation
  • One-year-olds: kittens weigh between eight to 15 pounds

To make sure your kitten is hitting the appropriate developmental markers, keep up with regular veterinarian visits. Because your kitten needs crucial vaccinations in their early weeks and months, it’s best to start taking them to your vet when they’re 2 months old or slightly before that.

Regular medical visits will provide your vet with a chance to make sure that your kitten is developing appropriately.

When is a kitten considered fully grown?

Assistant director of the Animal Medical Center of Mid-America, Dr. Nicole Fulcher, expands on that point. Fulcher says although kittens generally stop growing at 12 months that they aren’t considered fully grown until they’re 18 months old.

when do cats stop growing male kitten

When do male cats stop growing?

The sex of your cat and whether they’re neutered also play a key role in your kitty’s growth. Like female kittens, male kittens tend to stop growing at 12 months and reach their full adult size by 18 months.

It’s when these male kittens are neutered (or left intact) this question gets a little more complicated. We know for a fact that neutering cats affects their hormone levels and that their metabolism slows down a bit. But when it comes to physical size, we haven’t been able to find any concrete scientific evidence*.

What we know from experts and veterinarians, like Dr. Demos, is that your male kitten’s growth is more than their body mass. For one, their urethra is still growing.

Because of this, Demos advises cat parents to wait until their male cat is five months before neutering them. By neutering your male kitten at five or six months, you allow their urethra to grow large enough to pass urinary crystals and stones more easily. This is SO important because urinary obstructions from these masses can lead to life-threatening complications.

What should I feed my kitten?

In their kittenhood, cats grow “exponentially.” A balanced diet is key, but kittens also have distinct nutritional needs.

For one, growing kittens need three times more energy than adult cats. So, they need to eat higher protein and higher calorie diets than adult cats. It’s best to feed kittens at least three meals a day and consider free-feeding them, especially if they’re very energetic and physically active.

The ASPCA recommends kittens eat a combination of wet and dry cat food specifically formulated for kittens up until they turn 1 year old. The best, highest quality kitten foods will have one of the following written clearly on their labels.

 “Meets the nutritional requirements of kittens established by the American Association of Feed Control Officials (AAFCO)” or, “Complete and balanced nutrition for kittens based on AAFCO feeding trials.” 

If you are having trouble deciding what food is right for your kitten, be sure to check our articles on kitten nutrition. You could always reach out to your veterinarian as well.

They’ll fill you in on feline nutrition and there’s a good chance that they might even have a few free food samples! You can see which food your kitten likes the best, and they’ll be getting all the right nutrients they need to grow!

Key points on when do cats stop growing

The most literal reply to when cats stop growing is 18 months for the average cat.

As we’ve explored in this deep dive into your kitten’s development, there are many factors that determine this growth rate.

The sex of your kitten, genetics, breed traits, and access to healthy food all contribute to their growth.

The most important thing to takeaway is that when your kitten is done growing is subject to change. While feline health experts and scientists can share average numbers with us, these aren’t one-size-fits-all facts.

You should regularly take your kitten to the vet throughout their early weeks so your veterinarian can make sure they’re meeting their developmental milestones and that they’re growing up into a strong and healthy kitty, ready to take on the world!

Final note * If you’re a veterinarian, feline health expert, or scientist who has any facts about the size and growth difference between neutered vs. intact male cats, please leave us a comment below or contact us! We’d love to hear from you.

Victoria Tomis
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