Kitten Milestones from 0 to 12 Months: What Happens When

Kitten development runs on a schedule tight enough to use as a health check. Eyes open between seven and fourteen days, baby teeth at about three weeks, adult canines at four to five months, and a queen can come into her first heat at five, before many owners have booked the spay. Knowing what belongs in each window tells you when something is late — and late is usually the first symptom a kitten shows.

Weeks 0-3: almost all body

A newborn is blind, deaf and largely helpless: eyes sealed, ear canals closed, finding the teat by smell and warmth. Eyes open between day seven and day fourteen, the ear canals at about two weeks, and the true eye colour settles between two and three months.

Weight is the only reliable scoreboard. A kitten should gain 10 to 15 g a day and roughly double its birth weight by week two. By three weeks it can stand, walk with a wobble and hiss — a threat display that appears before it can do anything about a threat.

Month-by-month milestones

Age	Body	Behaviour and skills
0-1 week	90-120 g; eyes and ears sealed	Nurses, sleeps about 90 percent of the time
1-2 weeks	Eyes open day 7-14; ears open; 200-260 g	Recognises the queen by scent; crawls toward warmth
3 weeks	250-330 g; deciduous incisors erupt; walks	First play, first hiss; can right itself
4 weeks	350-450 g; canines and premolars arriving	Litter box use begins; starts sampling solid food
5-6 weeks	500-650 g; full baby teeth (26)	Social play peaks; learns bite inhibition from littermates
7-8 weeks	700-900 g; runs, climbs, lands well	Weaned; the usual minimum age for rehoming
2-3 months	1.0-1.5 kg; first vaccinations	Socialisation window closing; fear responses sharpen
3-4 months	1.5-2.0 kg; adult incisors replace baby ones	Chewing everything; carries and bats objects
4-6 months	2.0-3.0 kg; adult canines and premolars in	Sexual maturity: first heat, or spraying and mounting
6-9 months	2.5-4.0 kg; 75-90 percent of adult weight	Independence, boundary testing, longer naps
9-12 months	3.2-4.5 kg; 6 mm+ of growth left at most	Settles into adult social patterns; still playful

Track the numbers with the weight tracker: a late milestone is easier to judge against a curve than against memory.

Weeks 3-7: the window that closes

The socialisation window is the most consequential stretch of a cat's life, and it is short. Between roughly three and seven weeks a kitten learns what is safe: other species, handling, noises, surfaces. It starts closing around nine weeks and is shut by fourteen. A kitten that meets fifty gentle strangers before sixteen weeks is a different adult from one that met three.

This is why eight weeks is a floor, not a target. Between six and eight weeks the queen and littermates are still teaching bite inhibition: that a bite hurts and play stops. Kittens separated at six weeks are noticeably more likely to mouth hard as adults, and twelve to fourteen weeks is the better rehoming age.

Two to four months: teeth and the second series

The baby teeth start being replaced at three to four months, incisors first, then canines and premolars by six. Kittens chew now because their gums ache: wires, plants, shoelaces, fingers. Offer cold firm things to bite and put cables out of reach; the habit peaks around five months and fades once the adult set is complete.

Two to three months is also when the vaccine series runs. Follow the vaccine calendar, not the diary: the intervals carry the protection, and the final dose belongs at sixteen weeks or later.

Four to six months: adolescence starts early

Sexual maturity arrives well before social maturity. A queen may have her first heat at five to six months, occasionally four; a tom begins spraying and mounting between six and nine months, and the urine changes smell before the behaviour appears. Hence the case for neutering at four to six months, before marking becomes habit and while the animal is small enough to recover quickly.

Adolescence shows up as testing: the kitten that came when called at ten weeks ignores you at six months, climbs the curtains, and plays rough the moment you sit down. Nothing is broken. Play needs are peaking while confidence is new, and two short wand-toy sessions do more than any amount of telling off.

Six to twelve months: filling out, not growing up

Length growth is largely finished by eight months in a domestic shorthair; after that the cat adds muscle and fat, not height. The curve flattens to 40-60 g a week between six and nine months and nearly stops by a year, and a lanky, long-legged seven-month-old is normal, not underfed.

Large breeds are the exception and need their own timeline: a Maine Coon keeps growing for three to four years, and a chart built for a shorthair will make it look overweight long before it is. Social maturity, meanwhile, arrives at two to three years, which is why a one-year-old still acts like a teenager.

What should be true at twelve months

By the first birthday a cat should be near its adult weight, have all thirty adult teeth, be vaccinated to the sixteen-week standard plus a one-year booster, be microchipped and neutered, tolerate handling and claw trims, use the litter box reliably, and play with toys rather than hands. Anything missing is cheaper to fix at twelve months than at three years.

Two milestones are worth flagging to a vet rather than waiting out: still not walking at four weeks, and no adult teeth by six months. Both are uncommon and cheaper to investigate early. The kitten section covers feeding and first-week setup.

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