Overview
Most kittens reach full size between 12 and 18 months, but their growth can reveal early signs of health issues too. Research shows that kittens who gain weight too fast are more likely to become overweight adults, while regular weighing can help spot potential illnesses early. Kitten growth doesn’t happen all at once, and it varies between breeds.
From birth to eight weeks: Newborn phase
Newborn kittens are small, blind, and utterly dependent on their mother. In their first two weeks, they spend most of their time sleeping and feeding, but significant changes are already happening.
When do kittens open their eyes?
Kittens are born with their eyes closed. Their eyes usually start to open between seven and 14 days after birth, but their vision remains blurry at first. Around the same time, their ears begin to unfold and their sense of hearing develops.
By three weeks, they take their first steps and start exploring their world. If you’ve adopted a young kitten, knowing how to tell the age of a cat can be tricky, but their eyes, teeth, and mobility offer good clues. For example:
Eyes still closed: under 10 days old
Starting to walk and play: 3–4 weeks
Full set of baby teeth: around 6 weeks
Read more: Is my cat a healthy weight?
Two to six months: playful, growing fast
This is when growth speeds up. You might be surprised at how quickly your kitten’s body and behaviour change.
Between eight and 16 weeks, kittens play, wrestle, climb, and test their limits. They’ll also go through teething and start replacing baby teeth with adult ones. They’ll still need regular meals, feeding 3-4 times a day until transitioning to twice daily at around 6 months old.
At this stage, you can start using a kitten growth chart to monitor their progress. Remember, regular weighing isn’t just about tracking progress, it can help spot early signs of illness, like sudden plateaus or drops.
For example:
Kitten age | Average weight |
8 weeks | 900g |
12 weeks | 1.4–1.8kg |
16 weeks | 2.2–2.5kg |
Weights vary by breed, but regular weigh-ins will help spot any issues early.
Download our kitten weight tracker — this is great to print and stick to your fridge
Six to 12 months: looking grown-up
By six months, most kittens are around 80% of their adult size. They start to look more mature, and their growth begins to slow. While a Siamese or domestic shorthair may be almost done growing, larger breeds like Maine Coons or Ragdolls will keep growing for much longer.
Neutering is usually recommended by 4–6 months, before puberty sets in.
You can usually transition to two meals a day around 6 months, and to adult food around 12 months.
Continue using your kitten growth chart to track weight — it should now start to plateau.
Beyond 12 months: when growth stops
Most cats reach full growth by around 12–18 months. Some might still fill out a little after that, but their bones have usually stopped growing. Larger breeds may continue to gain size until they are around two years old.
Signs your kitten has stopped growing:
Height and weight remain steady
Appetite levels off
Adult proportions (head, paws, body) look balanced
If you’re unsure whether your kitten is still growing, your vet should be able to confirm their approximate age by examining their teeth, weight, and even bone growth. That’s especially useful if you’ve adopted a rescue cat and need to tell the age of a cat more accurately.
Kitten growth timeline at a glance
Age | Key milestones |
0–2 weeks | Eyes closed, relies on mum, starts to open eyes by seven to 14 days |
3–4 weeks | Starts walking, baby teeth appear |
6–8 weeks | Weaned, playful, uses litter tray |
3 months | Rapid growth, baby teeth begin to fall out |
6 months | Most adult teeth in place, may reach 75–80% adult weight |
12 months | Adult size for most cats; transition to adult food |
18+ months | Fully mature, especially in larger breeds |
What science says about helping your kitten grow
How a kitten’s mum can influence their weight
This long-term study showed that kittens born to overweight mothers were more likely to become overweight themselves, especially males. Higher birth weight also increased the risk, while kittens from larger litters were less prone to weight gain. The research suggests that early monitoring of birth weight and the mother’s condition can help predict whether a kitten might need more support in maintaining a healthy weight later on. If your kitten was born with a high birth weight or their mother was overweight, they may require closer monitoring to prevent weight gain.
Using growth charts to spot weight issues early
Researchers in this study developed new growth charts for domestic kittens using data from vet practices. They found that kittens who quickly moved up two or more weight “centile” lines were more likely to become overweight by adulthood. Female kittens generally tracked more steadily, while males gained weight faster. Using a growth chart can help owners and vets track weight, and if your kitten suddenly jumps a few centile lines, it might be a sign they’re gaining too fast.
Growth and illness in foster kittens
A study of more than 200 kittens in rescue centres found that most gained weight steadily, even in less-than-ideal conditions. Daily weighing proved vital, especially for spotting subtle signs of illness like lethargy, which was linked to slower weight gain. Surprisingly, food sources didn’t greatly affect growth. It found that monitoring weight helps catch issues early, improves survival, and ensures better care for kittens from day one.
Need more information?
Kittens stop growing at different times depending on their breed, size, and health, but most reach their full size between 12 and 18 months. A kitten growth chart is a great way to track changes, and regular weight checks help catch any issues early.
From the moment their eyes open to the day they curl up on your lap as an adult cat, every stage of kittenhood is special. Knowing how to tell the age of a cat, what to expect next, and how to support their development gives your pet the best chance of growing up healthy.
If you’re ever unsure, find a vet near you for expert advice, or join our Pet Health Club to get regular check-ups, weight monitoring, and all the support your kitten needs to thrive.
Join the club today
Get regular health checks, vaccinations, and more, all included in your plan.
Show references
Salt, C., German, A.J., Henzel, K.S. and Butterwick, R.F., 2022. Growth standard charts for monitoring bodyweight in intact domestic shorthair kittens from the USA. PLOS ONE, 17(11), p.e0277531. https://doi.org/10.1371/journal.pone.0277531
Berliner, E.A., Scarlett, J.M., Cowan, A.C. and Mohammed, H., 2022. A prospective study of growth rate, disease incidence, and mortality in kittens less than 9 weeks of age in shelter and foster care. Journal of Applied Animal Welfare Science, 25(6), pp.607–622. https://doi.org/10.1080/10888705.2021.2021409
Opsomer, H., Liesegang, A., Brugger, D. and Wichert, B., 2022. Growth curves and body condition of young cats and their relation to maternal body condition. Animals, 12(11), p.1453. https://doi.org/10.3390/ani12111453
American Veterinary Medical Association (AVMA), 2021. Pet Ownership and Demographics Sourcebook. Schaumburg: AVMA.
Cornell University College of Veterinary Medicine, 2020. Feline Development and Socialization. Ithaca: Cornell Feline Health Center. Available at: https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center
Hill’s Pet Nutrition, 2023. Kitten Developmental Milestones. Available at: https://www.hillspet.com/cat-care/kitten-care/kitten-growth-milestones
Rezende, M.P.F., et al., 2020. Radiographic growth plate closure times in domestic cats. Journal of Feline Medicine and Surgery, 22(2), pp.197–203. doi:10.1177/1098612X19877836.
Royal Canin Vet Focus, 2021. Understanding the Stages of Kitten Development. Vet Focus. Available at: https://vetfocus.royalcanin.com/en/kitten-development-stages
Medically reviewed by Lizzie Youens, BSc(Hons) BVSc MRCVS
Published on 15/05/2025 • Reviewed on 15/05/2025