How Long Do Cats Grow? Which Differences Are Real and Which Are Noise

Most domestic cats stop growing between 7 and 12 months old, and the width of that range comes from which endpoint you measure. The Merck Veterinary Manual puts the weight plateau at 150–160 days and states that growth "is usually completed within 200–220 days." The WALTHAM centile curves published by Salt and colleagues in PLOS ONE in 2022, built from Banfield Pet Hospital records, run from 8 to 78 weeks, and in that data the median male kitten keeps climbing until about 10 months while females track close to the median throughout. Bone finishes last. In a study of 783 feline radiographs, the distal femoral growth plate was assessed at 13 months and the tibial tuberosity at 17. Large pedigree breeds are the genuine exception, and the Cat Fanciers' Association says a Maine Coon "can take up to three years to reach full growth."

Two growth clocks run at once, and they stop months apart

A kitten's weight and a kitten's frame are separate measurements with separate endpoints, and most confusion about how long cats grow comes from collapsing them into one number.

Weight moves first and fastest. Merck gives a normal birth weight of 90–100 g and a gain of 50–100 g per week, exceptionally rapid through the first three to four months. Then it flattens. The plateau begins at 150–160 days, and Merck considers growth usually complete within 200–220 days, roughly seven months.

Population data is less tidy. In the centile curves Salt, German, Henzel and Butterwick built from Banfield's records, the median male trajectory crosses the 75th centile at about seven months before levelling out between the 75th and 91st lines at about ten months. Female kittens deviate far less.

The frame runs behind both. Perry, Fordham and Arthurs examined 783 radiographs of cats' hind limbs, using assessment ages drawn from earlier literature: greater trochanter at 7 months, proximal femur and proximal tibia at 9, distal femur at 13, tibial tuberosity at 17. Individual cats held plates open considerably later.

The 2021 AAHA/AAFP Feline Life Stage Guidelines run the kitten stage from birth to one year, which for an owner is the sane planning date. Use Merck's eight to twelve months to decide when to switch foods, and ten to twelve months to decide when a mixed-breed cat's adult size is settled.

Which changes on a growth chart are real, and which are noise

WALTHAM's guidance for its own kitten charts is to weigh every two to four weeks up to six months, then every one to three months until the cat is fully grown. It discourages weighing more often, because meals and litter box visits make a kitten's weight appear to fluctuate. The instrument is fine; the sampling rate manufactures the false signal.

The charts also define a real change. There is no ideal centile line; the 50th is not a target and neither is the 99.6th. What matters is the shape of one cat's line: a move of more than two centile lines in either direction, or a flat line before adult weight, is a warning sign.

Until roughly the start of 2024 I told owners to weigh weekly for the whole first year, on the theory that more data could only help. I stopped. In freezer-loss work, a probe sampling every thirty seconds renders a healthy appliance's duty and defrost cycle as a sawtooth that looks like failure; the record that decides a claim is the daily minimum and maximum. Weekly kitten weights past four months lay meal-sized noise over a curve whose genuine monthly change has shrunk to about the same magnitude.

The first month is the exception. Merck's neonatal protocol is daily weights for two weeks, then every three days until one month, because a healthy neonate gains 5–10% of body weight per day and that daily gain is the vital sign. A plateau then is an emergency.

The procedure I would hand a first-time owner is short:

1. Use one scale all year and weigh before a meal, so each number means the same.
2. Weigh every two to four weeks until six months, then every one to three months until the line goes flat.
3. Plot on the sex-specific WALTHAM chart; the male and female curves separate.
4. Pair every weigh-in with a hands-on body condition score.
5. Call the vet if the line crosses more than two centiles or flattens before adult weight.

What body condition score measures that the scale cannot

Weight alone answers little about whether growth is going well, because it cannot separate frame from fat. The 9-point body condition score closes that gap. Laflamme validated it for cats in Feline Practice in 1997, and WSAVA publishes it in its global nutrition toolkit, running from 1 for emaciated through 5 for ideal to 9 for grossly obese.

The validation numbers set your expectations. Bjornvad and colleagues at the University of Copenhagen scored 72 indoor-confined neutered domestic shorthairs against dual-energy X-ray absorptiometry, reporting in the American Journal of Veterinary Research in 2011. Body condition score correlated with percentage body fat at r = 0.87, ahead of body weight at 0.74 and girth at 0.78. Shoveller's evaluator study later put the veterinarian's correlation with DXA fat at 0.80. The score is a skill, not a glance.

A second measurement does what the score cannot, and I had not heard of it until I went looking. The Feline Body Mass Index combines rib cage circumference at the ninth rib with a leg index measurement, taped from the middle of the patella to the dorsal tip of the calcaneal process on the left hind limb. That leg index is skeletal, so it does not move when the cat gains or loses fat, which makes it the closest an owner gets to a direct reading of frame growth. Iwazaki and Mori's 2026 review in Animals is candid about the limits: the arithmetic is fiddly, and the ninth rib cannot be located on a severely obese cat.

I should be plain about where my competence stops. I have never been trained to palpate a cat, and the evaluator data above says untrained scoring drifts, so nobody should take my body condition score over their vet's. What I vouch for is the half that matches my job: reading a series of measurements over time and telling a genuine break from a wobble. That transfers. Palpation does not.

Do cats stop growing after neutering?

No, and the evidence leans the other way. Neutering delays growth plate closure, so a neutered cat's long bones usually get more time to lengthen.

Root, Johnston and Olson ran the direct test in Veterinary Radiology and Ultrasound in 1997. They gonadectomised kittens at 7 weeks or at 7 months, kept an intact group, and radiographed the right forelimb until the distal radial growth plate closed. Closure was delayed in gonadectomised males and females alike, and final radial length came out significantly greater in every gonadectomised group. Perry's team found the same direction in the hind limb, in males only: delays at the greater trochanter, distal femur and tibial tuberosity, none in females, and open distal femoral plates as late as 24 months in neutered males against 15 in entire males. They added that the clinical significance for fracture risk remains unclear.

None of this argues for delaying surgery. The Veterinary Task Force on Feline Sterilization reviewed the literature in January 2016 and found no evidence of increased complications or long-term harm in cats sterilised under five months. The AVMA endorsed the consensus statement in June 2017, alongside the AAFP, AAHA, the Association of Shelter Veterinarians, CFA and TICA. Five months is now the recommended age for cats not intended for breeding.

What changes after neutering is weight, and the mechanism is the part owners get backwards. Wei and colleagues at UC Davis followed nine adult male domestic shorthairs, mean weight 5.2 kg. Total energy expenditure adjusted for lean body mass did not change from before neutering to nine days after. Food intake did: 62 g a day before, 70 g at day nine, staying elevated for roughly 27 weeks on free access. Six months on, body weight was up 20% and fat mass up 75%, from 0.8 kg to 1.4 kg, lean mass unchanged. Fettman's 1997 work pointed the same way.

I once condemned a chest freezer's compressor. The contents had thawed, the restart notes read wrong to me, and I paid to have the compressor swapped. The fault was a lid gasket I had folded under a wire basket myself, holding the seal open by a few millimetres. I paid for a compressor with nothing wrong with it, and I had already binned food I could have refrozen. Blaming a neuter for weight gain has that shape. The mechanism everyone condemns, the metabolism, is running fine. The open seal is the food bowl, and nobody measured it.

Mixed-breed cat versus large pedigree breed: what actually differs

The Maine Coon is the exception every article mentions, and owners routinely apply it to cats it does not describe.

| Property | Mixed-breed cat | Maine Coon (pedigree large breed) | Source | |---|---|---|---| | Weight growth largely finished | 200–220 days | still filling out past 12 months | Merck; CFA | | Adult size settled | 10–12 months | up to 3 years | Salt et al.; CFA | | Typical adult weight | 2.7–5.4 kg (6–12 lb) | males often 20 lb or more | Britannica; CFA | | Adult length | male ~71 cm, female ~51 cm | living record 120 cm | Britannica; Guinness | | Growth plate closure | no significant breed effect | no significant breed effect | Perry et al. | | Switch to adult food | 8–12 months | 8–12 months | Merck |

The fifth row surprises people. Perry's dataset included 96 pedigree and 687 non-pedigree cats, and found no statistically significant effect of breed at any physis examined. A Maine Coon's three years go into filling out, meaning chest breadth, muscle and coat, rather than bone that lengthens indefinitely. The CFA show standard asks judges to allow for slow maturation, an instruction about proportion in the ring, not a claim that the skeleton is open at 36 months.

Guinness verified Barivel, an Italian brown tabby Maine Coon, at 120 cm as the longest living domestic cat on 22 May 2018, aged two. His length was settled well before three.

The strongest case against me is real, and I grant it first. Breed does move the endpoint, and an owner of a large-breed kitten who applies domestic-shorthair timelines will see a curve still climbing at fourteen months and assume something is wrong. Worse for my position, Perry's pedigree group was 96 cats of assorted breeds rather than a Maine Coon cohort, so it cannot settle whether Maine Coon plates close on anyone else's schedule. I do not have a study that does. What I have is the shape of the claim: CFA describes slow maturation and a mature male at 20 pounds or more, and neither is a statement about bone lengthening. For a mixed-breed kitten, borrowing that timeline to explain a flat curve at nine months is how a real problem gets a folk excuse.

One caution on length, the number most often quoted and least often sourced. The widely repeated 46 cm, or 18 inches, from nose to tail base traces to Wikipedia rather than to any measured population study I could find, and Britannica's own figures disagree with it, giving about 71 cm for a full-grown male and 51 cm for a female. Measure your own cat instead of ranking it against a number with no cohort behind it.

How diet energy density changes what you see on the scale

Every growth curve is partly a record of what came out of the bag, and the label gives the conversion. AAFCO's Model Regulation PF9, amended in January 2013 with enforcement grace ending in June 2015, requires a calorie content statement on non-exempt cat and dog food labels: metabolisable energy in kilocalories per kilogram as fed, kilocalories per household measure such as a cup, and whether the figure was calculated or fed.

That number is the only honest way to compare two foods. AAFCO's nutrient profiles use a reference density of 4,000 kcal ME per kilogram of dry matter, and a cat food qualifies as light or low calorie only below 3,250 kcal/kg at under 20% moisture. Moisture is why an as-fed comparison between canned and dry tells you almost nothing.

The arithmetic that matters for a growth chart is mine, not a published finding. Moving a kitten from a 3,600 kcal/kg dry food to a 4,200 kcal/kg dry food at the same weight of food raises calorie intake by about 17% with nothing changed about the cat, which is enough to bend a centile line. Merck puts the switch to adult food between eight and twelve months, and that switch is usually a density change as well as a formula change. When a curve moves within weeks of a new bag, read the label before you examine the cat.

Questions owners actually ask

At what age is a cat fully grown?

Most mixed-breed cats are fully grown between 10 and 12 months. The Merck Veterinary Manual places the weight plateau earlier, at 150 to 160 days, with growth usually complete by 200 to 220 days. The 2021 AAHA/AAFP Feline Life Stage Guidelines run the kitten stage to one year, which is the safer planning date for an owner.

Can you tell how big a cat will get?

Not precisely for a mixed-breed kitten. Knowing both parents is the strongest clue available, and a pedigree gives you a documented breed range. Frame measurements help more than weight does: the patella-to-calcaneus leg index used in the Feline Body Mass Index tracks skeleton rather than fat, so it stays stable as body condition changes.

How much more do cats grow after 6 months?

Less than most owners expect. In the WALTHAM centile data the median male kitten keeps climbing until about 10 months, while females stay close to the median throughout. The remaining gain arrives at tens of grams per week rather than the 50 to 100 grams per week Merck reports for the first three to four months.

When do cats stop growing in length?

Length depends on growth plates, which close after the weight curve has flattened. Perry and colleagues assessed the distal femoral physis at 13 months and the tibial tuberosity at 17 months across 783 feline radiographs. Individual cats held plates open later still, as late as 24 months at the distal femur in neutered males.

Do cats stop growing after neutering?

No. Gonadectomy delays growth plate closure, so neutered cats often finish slightly longer in the long bones. Root and colleagues found final radial length significantly increased in every gonadectomised group. Weight gain after neutering comes from eating more. Wei's 2014 study found energy expenditure unchanged while food intake rose within nine days.

Is the kitten following its own growth curve?

That question matters more than the number on the scale. Plot each weight on a sex-specific centile chart and watch the shape of the line. WALTHAM treats a move of more than two centile lines in either direction, or a flat line before adult weight is reached, as a warning sign worth a veterinary appointment.