Kitten Development by Month: Size, Teeth and Milestones from Birth to 12 Months

A kitten changes faster in its first year than at any other time of its life. At 1 month it fits in the palm of your hand, weighs around 400–500 g and is just starting to walk steadily and explore. By 2 months it weighs roughly 750–1000 g, has a full set of baby teeth, eats solid food and runs, climbs and plays. At 3–4 months it is about a third to half of its adult weight, and most domestic cats are close to full size by 12 months. This guide walks through each stage month by month: how big your kitten should be, what it should be able to do, and which care tasks belong to that age.

The short answer

• 1 month (4 weeks): about 400–500 g, eyes and ears open, wobbly walking, first baby teeth coming in, starting to try the litter box.
• 2 months (8 weeks): about 750–1000 g, full set of baby teeth, weaned onto kitten food, very playful. First vaccines are usually due around now.
• 3 months (12 weeks): about 1.2–1.5 kg, confident and fast, adult eye color settling. Second round of vaccines. A common age to go to a new home.
• 4–6 months: about 1.7–3.2 kg, baby teeth fall out and adult teeth come in, sexual maturity can start. Talk to your vet about neutering.
• 6–12 months: growth slows, the kitten fills out into an adult shape. Most cats are fully grown at 12–18 months; large breeds keep growing for years.
• Watch the trend: a kitten that keeps gaining and keeps reaching its milestones is almost always doing well. A kitten that stalls or falls behind needs a vet.

Kitten development at a glance

The weights below match our kitten weight chart by week and month, which has the full week-by-week figures. They are for an average domestic shorthair; large breeds and big litters can sit outside the ranges and still be healthy.

Week 0 to 4: the newborn kitten

Birth to 2 weeks

Newborn kittens are born with their eyes closed and their ears folded flat. They cannot see, hear well, or keep themselves warm, and they spend almost all their time sleeping and nursing. A healthy newborn weighs about 90–110 g and should roughly double that weight before it is 2 weeks old.

The eyes usually open between 7 and 14 days. All kittens start with blue eyes, whatever color they will have as adults. Until about 3 weeks of age the mother licks her kittens to make them pee and poo; orphaned kittens need a person to do this gently with a warm, damp cloth after every feed.

2 to 4 weeks

This is the transitional stage. The ear canals open and the ears begin to stand up, the kitten starts to respond to sound, and the first wobbly steps appear at around 3 weeks. The first baby teeth (the small front incisors) usually break through at around 2 to 4 weeks.

Kittens also start to show interest in a shallow litter tray at about 3 to 4 weeks. Routine deworming often starts at around 2 to 3 weeks; how often to deworm a cat has the full schedule.

1 to 2 months: weaning, play and the socialization window

Between 4 and 8 weeks a kitten goes from a milk-only diet to eating solid kitten food. Weaning usually starts at around 4 weeks with wet kitten food softened with kitten milk replacer, and most kittens are fully weaned by 8 weeks. Never give cow's milk.

By 6 to 8 weeks the full set of 26 baby teeth is in. Coordination improves week by week: kittens run, pounce, wrestle with littermates and climb anything they can reach.

This period also contains the socialization window, roughly from 2 to 7 weeks of age. What a kitten experiences now shapes how relaxed it will be as an adult. Gentle daily handling by different people, normal household sounds and short, positive experiences make a big difference. A kitten with little human contact in these weeks can still become a good companion, but it usually takes more time and patience.

At about 2 months a kitten is still small enough to sit in two cupped hands, but it is no longer fragile. This is a good age for a first health check; our guide to the first vet visit for a puppy or kitten explains what happens and what to bring.

2 to 4 months: vaccines, adult eye color and a new home

A typical kitten weighs about 0.8–1.0 kg at 2 months, 1.2–1.5 kg at 3 months and 1.7–2.0 kg at 4 months. That is the fastest growth phase after the newborn weeks, often around 100 g a week.

Key changes in these months:

• Eye color: the blue kitten eyes start to change at around 6 to 8 weeks, and the adult color usually settles by about 3 to 6 months.
• Vaccines: the first core vaccines are usually given at around 8 to 9 weeks, with further doses every 3 to 4 weeks until about 16 weeks of age. The cat vaccination schedule by age shows the timing.
• Leaving the mother: kittens should not leave their mother before 8 weeks. Many shelters and breeders wait until around 12 weeks, when the kitten is weaned, partly vaccinated and better socialized.
• Adult teeth: from about 3 to 4 months the baby incisors start to fall out and adult teeth push through.

Kittens at this age need about four small meals a day of a complete kitten food. How much to feed a dog or cat explains how to work out daily portions as your kitten grows.

4 to 6 months: teething and the start of adolescence

Between 4 and 6 months the kitten keeps growing quickly, from about 1.7 kg to 2.7–3.2 kg. Its legs and body look longer and lankier, and its personality becomes clearer.

Teething is in full swing. The baby teeth are replaced by 30 adult teeth, and the full adult set is usually in place by about 6 to 7 months. You may find tiny teeth on the floor, or see your kitten chew more than usual; both are normal. A baby tooth that is still there when the adult tooth next to it has fully erupted should be checked by a vet.

Sexual maturity can arrive surprisingly early. Some female kittens come into heat from about 4 to 6 months, and males may start to spray. This is why vets often discuss neutering at around 4 to 6 months. The right timing depends on your kitten, so ask your vet. Neutering lowers energy needs, so check the weight curve after the operation and adjust portions if the kitten starts to gain too fast.

6 to 12 months: the teenage kitten

Growth slows down noticeably after 6 months. Most kittens weigh about 2.7–3.2 kg at 6 months and 3.2–4.5 kg at 12 months, and the weekly gain becomes small. From now on, body condition tells you more than the scale: you should be able to feel the ribs under a thin layer of fat and see a waist from above.

Most domestic cats reach about 80–90% of their adult weight by 9 to 12 months and are fully grown somewhere between 12 and 18 months. Many owners switch to adult food at around 12 months; large breeds may stay on kitten food longer, as your vet advises. If you are curious how old a 1-year-old cat is in human terms, see dog and cat years to human years.

Large breeds grow for longer

Breed makes a big difference to the timeline. Maine Coons, Norwegian Forest Cats, Ragdolls and Siberians are bigger at every age and may not reach full adult size until 3 to 5 years old. Slender breeds such as the Siamese or Devon Rex often finish near the lower end of the ranges. The cat weight chart by breed lists adult targets for common breeds.

How to track your kitten's growth

1. Weigh your kitten on a digital kitchen scale: daily in the first weeks, weekly from 8 weeks to 6 months, then every 2 to 4 weeks.
2. Write down each weight with the date, and compare it with the kitten's own previous weights rather than only with a chart.
3. Note milestones as they happen: eyes open, first steps, litter box use, weaning, lost baby teeth.
4. Keep vaccine and deworming dates in one place so the next dose is never missed.
5. Take your notes to every vet visit. A clear record helps the vet spot a problem early.

Log your kitten's weight, vaccines and milestones in PetVitals. The app draws the growth curve, reminds you when the next vaccine or deworming is due and keeps every vet visit in one place.

When to call the vet

Kittens have small reserves and can get sick quickly, so do not wait and see with these signs:

• A newborn that loses weight over 24 hours (after the normal first-day dip), or a kitten under 8 weeks that does not gain for two days in a row.
• A kitten that is clearly smaller, weaker or slower than its littermates and keeps falling further behind.
• Eyes that have not opened by about 2 weeks, or eyes that are swollen, crusted or have a discharge.
• Not walking steadily by about 4 to 5 weeks, a head tilt, or repeated falling.
• Diarrhea, vomiting, not eating, sneezing with a blocked nose, a pot belly, or a cold body.
• A baby tooth still in place next to a fully erupted adult tooth, or bleeding and swelling in the mouth.

Keep a weak or cold kitten warm while you arrange the visit, and do not force-feed a chilled kitten. Our list of signs your cat is sick covers other changes worth acting on.

Every kitten follows its own curve. If yours keeps gaining, keeps reaching its milestones and stays bright and curious, it is on the right track.