When Do Cats Stop Growing? Ages, Weight Chart and Big Breeds

Most cats stop growing at around 12 months old. By their first birthday they are close to full size, and vets count them as young adults from then on. Females are often done at 10 to 12 months, while males can keep filling out until about 18 months. Large breeds such as the British Shorthair, Maine Coon, Ragdoll and Norwegian Forest Cat take much longer and are only fully grown somewhere between three and five years.

How long do kittens keep growing?

An average domestic cat reaches its adult size between 12 and 18 months. Growth is fastest in the first six months. A kitten roughly doubles its birth weight in its first week, and between four and five months it gains around 100 g a week, the most intense weight gain of its life. After six months growth slows down, and in the second half of the first year it mostly adds muscle and a little weight.

Sex makes a difference. A female kitten has usually stopped growing by 10 to 12 months. A male often keeps going a bit longer, sometimes until he is a year and a half. You see that in the end result too: in almost every breed, males end up heavier than females.

What actually stops the growth is the closing of the growth plates. These are soft zones near the ends of the long bones where new bone is made. Once they turn to solid bone, the legs cannot get any longer. In an average cat this happens around the first birthday. Neutering can delay it slightly, more on that below.

Vets use fixed life stages. In the life stage guidelines of the American vet associations AAHA and AAFP, a cat is a kitten from birth to 1 year and a young adult from 1 to 6 years. International Cat Care divides it more finely and calls a cat of 7 months to 2 years a junior. How the stages continue into old age is covered in how long cats live.

Kitten growth chart: weight by age

The figures below are for an average domestic cat. Treat them as a rough guide. Breed, sex and the size of the parents all play a part, and a large-breed kitten will be well ahead of these numbers.

Age	Typical weight	Source
Newborn	50 to 150 g (2 to 5 oz)	PetMD
1 week	150 to 250 g (5 to 9 oz)	PetMD
2 weeks	250 to 350 g (9 to 12 oz)	PetMD
4 weeks	450 to 550 g (about 1 lb)	PetMD
6 weeks	650 to 750 g (1.4 to 1.7 lb)	PetMD
8 weeks	850 to 950 g (1.9 to 2.1 lb)	PetMD, Cats Protection
3 months	about 1.4 kg (3 lb)	PetMD feeding chart
4 months	about 2 kg (4.5 lb)	PetMD feeding chart
5 months	about 2.5 kg (5.5 lb)	PetMD feeding chart
6 months	about 2.9 kg (6.5 lb)	PetMD feeding chart
8 months	about 3.4 kg (7.5 lb)	PetMD feeding chart
10 months	about 4.1 kg (9 lb)	PetMD feeding chart
12 months and older	adult average 3.6 to 4.5 kg (8 to 10 lb), normal range roughly 3 to 6 kg	PetMD, Purina UK

The weekly figures are ranges. From three months the chart gives an average weight per month, so expect a female to sit a little under it and a male a little over. Cats Protection uses a simple rule of thumb for young kittens: about 100 g at birth and 100 g extra every week, which gives 900 g at eight weeks.

Weigh your kitten on the same scale and at the same time of day. A kitchen scale works for the first weeks. For an older kitten, weigh yourself holding the kitten and subtract your own weight. A kitten that stops gaining for several days, loses weight or stops eating needs to see a vet.

How to tell if your cat has stopped growing

• The weight levels off. Weigh your cat once a month for a few months. If the weight stays the same while your cat eats well and is not getting fatter, the growing is done.
• The body looks finished. The gangly teenage look with long legs and big ears fills out into an adult shape. In large breeds that stage can last for years.
• The age fits. An average cat of 12 to 18 months is fully grown. A Maine Coon of the same age is not.

Your vet can tell you more at the yearly check-up. On an X-ray the growth plates show whether a cat can still grow.

A cat that keeps getting heavier after 18 months is usually putting on fat. Purina UK puts it plainly: cats can still gain after they reach their adult size, but it is more likely to be fat. Ask your vet to check the body condition if you are unsure.

What affects how big your cat gets

• Breed: the biggest factor. A slim domestic shorthair is done after a year, a Norwegian Forest Cat after five. Small breeds such as the Singapura can be finished at nine months or earlier, according to PetMD.
• Sex: males grow for longer and end up heavier.
• Food: a kitten needs food designed for growth. Underfeeding or a poor diet can hold growth back. Good food lets a kitten reach its natural size. It does not make it grow faster or bigger than its genes allow.
• Health: worms, illness or a hard start in life can set a kitten back. If your kitten grows noticeably slower than its littermates, have it checked. Regular worming is part of that, see the best cat dewormers for how often.
• Neutering: it can make a cat grow slightly longer, see the next section.

Does neutering affect growth?

Yes, a little, and in a direction that surprises many owners. Neutering slightly delays the closing of the growth plates, so a neutered cat grows for a bit longer.

The best-known study is by Root and colleagues, published in Veterinary Radiology and Ultrasound in 1997. They X-rayed the front legs of kittens neutered at 7 weeks, kittens neutered at 7 months and kittens left entire. In both neutered groups the growth plates in the forearm closed later, and the forearm bone ended up slightly longer than in entire cats. Whether the cat was neutered at 7 weeks or at 7 months made no difference. PetMD says the same in plain terms: in neutered cats the growth plates often close later, so they can grow for longer.

In practice the difference in size is small. What you do notice is body shape. A tomcat that stays entire until after puberty often becomes bulkier, with a broad head and heavy cheeks. Purina UK notes that males neutered after sexual maturity are usually larger.

International Cat Care recommends neutering at around four months, before a cat becomes sexually mature, and says that neutering at that age does not cause problems with development, behaviour or health. For very large breeds such as the Maine Coon, it suggests discussing the timing with your vet.

The bigger effect comes after the operation. A neutered cat needs less energy and is more prone to weight gain, according to International Cat Care. Keep an eye on the scales and reduce the portion if your cat starts to put on weight.

When do large breeds stop growing?

The bigger the breed, the longer the growth takes. Breed registries such as the American CFA and the British GCCF give a few years for the large breeds. They still become sexually mature early: a Maine Coon kitten can be fertile at a few months old while it has years of growing ahead.

Breed	Fully grown at around	Source
Domestic cat (moggy, domestic shorthair)	12 months (males up to 18 months)	AAHA/AAFP, PetMD
British Shorthair	3 years (breed standard: 3 to 5 years)	CFA
Maine Coon	3 to 4 years	CFA, Royal Canin
Ragdoll	3 to 4 years	GCCF, CFA, Royal Canin
Norwegian Forest Cat	up to 5 years	CFA, Royal Canin

Maine Coon

The CFA gives around three years for the Maine Coon, many breeders say three to four, and some males keep getting broader until they are five. A grown male typically weighs 6 to 8 kg (13 to 18 lb). Because they grow for so long, a one-year-old Maine Coon still has a lot of filling out to do. Everything about the breed is in our Maine Coon guide.

Ragdoll

According to the GCCF, a Ragdoll is fully grown at around three to four years, and the CFA and Royal Canin say about four. The coat and colour also need time: the full colour only comes through after a few years. More in our Ragdoll guide.

Norwegian Forest Cat

The slowest of the group. The CFA and Royal Canin give up to five years before a Norwegian Forest Cat is fully grown. Males in particular keep gaining breadth and coat in those years.

British Shorthair

The British Shorthair is a slow grower too. According to the CFA it does not reach its full size until around three years of age, and the breed standard speaks of three to five years for full maturity. Males especially get wider and heavier in that time. A British Shorthair of one year is often still a lanky version of the solid, round-faced cat it will become.

Growing up: sexual maturity and the teenage phase

Stopping growing and growing up are two different things. Kittens become sexually mature from around four months, according to International Cat Care. A female usually has her first season at around six months, sometimes earlier, and can get pregnant at four or five months, even by a brother from the same litter. How a pregnancy goes is explained in how long cats are pregnant.

Cats Protection counts puberty from four to about twelve months. An entire male starts spraying strong-smelling urine to mark his territory, roams further from home and fights more. If that has already happened indoors, how to get rid of cat pee smell helps. Neutering at around four months prevents most of this.

Behaviour takes longest of all. Wild bursts of energy, biting hands during play and mood swings are normal for a cat between four and twelve months, and many cats stay playful and silly until they are two. Large breeds often stay kittenish for even longer.

When to switch from kitten food to adult food

Kitten food has more energy, protein and minerals than adult food, because a kitten needs them to grow. Once growing is done, that extra only adds extra weight.

• Average domestic cat: switch at around 12 months.
• Large breeds such as the Maine Coon and Norwegian Forest Cat: Royal Canin advises around 15 months, because they grow for longer.
• After neutering: a neutered cat needs less energy. Watch the weight and adjust the portion if your cat gains.

Change gradually, over about a week. Royal Canin gives this schedule:

Day	Kitten food	Adult food
1 and 2	75%	25%
3 and 4	50%	50%
5 and 6	25%	75%
7	0%	100%

If your cat gets diarrhoea or leaves the new food, go back a step and build up more slowly. If it carries on, call your vet. What makes a good adult diet is covered in our guide to feline nutrition, and if you want to keep costs down, see the best cheap cat food.

Frequently asked questions