When is a cat fully grown? The answer depends on its size: most cats are usually fully grown at about 12 months, but large breeds such as the Maine Coon can keep growing until they are 2 to 4 years old. Those are guides, not hard lines: a cat grows fast in its first year, then slows down, and it may fill out — gaining muscle and breadth — for months after it has stopped growing taller. This guide gives the growth ages by size, what 'fully grown' means, and when to switch from young to adult food. Every figure is a guide, because individual cats vary. The kitten weight predictor estimates adult weight from a kitten's current weight and age.
The short version is: small breeds finish growing first, large breeds last, and a cat is fully grown when it has reached its adult height and weight — which is not the same as being an adult. A cat that has stopped growing still needs training, socialisation, and care, and it should not be switched to adult food until it has finished growing, or it may not get the nutrients it needs. The kitten growth chart by size guide gives the growth shares by age, and the when is a cat considered a senior guide gives the senior thresholds by size.
When is a cat fully grown
The table below gives the age at which a cat of each size is usually fully grown, with the typical adult weight for that size. Use it to know when to expect your cat to stop growing — and when to switch from young to adult food.
| Size | Fully grown at | Typical adult weight |
|---|---|---|
| Small | About 12 months | 2–4 kg |
| Medium | About 12 months | 3–6 kg |
| Large | 12 months–2 years (Maine Coon up to 4 years) | 5–11 kg |
Read the table from top to bottom and the pattern is clear: the smaller the cat, the sooner it finishes growing. A toy dog is usually fully grown at 9 to 12 months, while a giant dog is usually fully grown at 18 months to 2 years. A cat is usually fully grown at about 12 months, but a large breed such as the Maine Coon can keep growing until it is 2 to 4 years old. The cat age calculator works out the human-age equivalent for any age.
What 'fully grown' means
'Fully grown' means a cat has reached its adult height and weight — but it does not mean it has stopped changing. A cat that has stopped growing taller may still fill out, gaining muscle and breadth, for months afterwards, and it may still be maturing in behaviour: a cat that is fully grown at 12 months may still be an adolescent in behaviour until it is 18 months or 2 years old. A cat that is fully grown should be switched to adult food, but it still needs training, socialisation, and exercise.
A cat grows fastest in its first few months: a kitten is about a fifth to a quarter of its adult weight at 8 weeks, about half at 6 months, and about four-fifths or more at 12 months, when small breeds are near-adult and large breeds are still growing. The kitten weight chart by age guide gives the growth shares by age, and the kitten age calculator by weeks guide gives the development at each age.
When to switch from young to adult food
Switch from young to adult food when your cat has finished growing: at about 9 to 12 months for a small breed, about 12 months for a medium breed, 12 to 18 months for a large breed, and 18 months to 2 years for a giant breed. For cats, switch at about 12 months, or later for a large breed such as the Maine Coon. Switch gradually, over a week: mix the new food with the old, increasing the new food a little each day, so the stomach has time to adjust.
Do not switch too early: a kitten that is switched to adult food before it has finished growing may not get the nutrients it needs, and it may grow more slowly or less well. Do not switch too late, either: an adult cat that is still eating young food will get too many calories, and it may gain weight. The kitten feeding schedule by age guide gives the feeding schedule from weaning to adulthood, and the cat food calculator works out the daily calories for any weight and stage.
Growth by breed
Growth varies by breed as well as by size: a breed that is large for its size will grow for longer than a breed that is small for its size, and a breed with a heavy frame will fill out for longer than a breed with a light frame. A cat that is a crossbreed will grow at a pace between its parents' breeds, and its adult weight will be between theirs — so a crossbreed's growth is harder to predict, and the ranges on this site are typical estimates, not guarantees for any one cat.
To judge your own cat's growth, weigh it every two weeks as a young animal, and write the result down: a single reading matters less than the line over weeks. A kitten that is gaining weight steadily is growing well; a kitten that is not gaining weight at all over two weeks, or that is losing weight, needs a vet check. The cat growth chart by breed guide gives the growth ages breed by breed, and the kitten weight predictor estimates adult weight from a kitten's current weight and age.
When to ask a vet about growth
Ask a vet if your kitten is not gaining weight at all over two weeks, if it is losing weight, if it is growing much faster or much slower than expected for its breed, or if it is limping, stiff, or in pain. A kitten that grows too fast can develop joint problems, especially in large breeds, and a kitten that grows too slowly may have a health problem. A vet can work out whether the growth is normal, and what to do about it.
Ask your vet, too, about when to switch from young to adult food: the ages above are guides, and your vet may move them earlier or later depending on your individual cat's breed, its weight, and its health. A cat that is overweight should be switched earlier, and a cat that is underweight should be switched later. The how much food should a kitten eat guide gives the calorie tables for young cats.
For related reading, see the kitten weight predictor, the kitten growth chart by size guide, the kitten weight chart by age guide, the kitten age calculator by weeks guide, the cat growth chart by breed guide, the kitten feeding schedule by age guide.
Frequently asked questions
When is a cat fully grown?
Most cats are usually fully grown at about 12 months, but large breeds such as the Maine Coon can keep growing until they are 2 to 4 years old. Those are guides, not hard lines.
When should I switch from kitten food to adult food?
Switch when your cat has finished growing: at about 9 to 12 months for a small breed, about 12 months for a medium breed, 12 to 18 months for a large breed, and 18 months to 2 years for a giant breed. For cats, switch at about 12 months, or later for a large breed such as the Maine Coon. Switch gradually, over a week.
Does 'fully grown' mean my cat is an adult?
Not quite — a cat that has stopped growing taller may still fill out for months afterwards, and it may still be an adolescent in behaviour until it is 18 months or 2 years old. A cat that is fully grown should be switched to adult food, but it still needs training, socialisation, and exercise.
How fast does a kitten grow?
A kitten grows fastest in its first few months: it is about a fifth to a quarter of its adult weight at 8 weeks, about half at 6 months, and about four-fifths or more at 12 months, when small breeds are near-adult and large breeds are still growing. Weigh it every two weeks, and write the result down.
How do I know if my kitten is growing well?
Weigh it every two weeks and write the result down: a kitten that is gaining weight steadily is growing well. A kitten that is not gaining weight at all over two weeks, or that is losing weight, needs a vet check. The line over weeks matters more than any single reading.
When should I ask a vet about growth?
Ask a vet if your kitten is not gaining weight at all over two weeks, if it is losing weight, if it is growing much faster or much slower than expected for its breed, or if it is limping, stiff, or in pain. A kitten that grows too fast can develop joint problems, especially in large breeds.
Results on this page are estimates for general information only and are not veterinary advice. If your pet is ill, underweight, overweight, pregnant, or has a health condition, consult your veterinarian before changing diet or care.