Kitten Week by Week: What to Actually Expect (Weeks 1 to 16)

TL;DR

A healthy kitten roughly doubles birth weight by week 2 and hits about 1 kg by week 8. Anything more than 10% off these targets for more than a few days is worth a vet call.
Eyes open between days 7 and 14. Ears open and start funnelling sound around day 10. Both lagging past day 18 is a soft red flag.
Weaning starts around week 4, not week 3. Pushing earlier usually causes diarrhoea and delays weight gain.
The hard socialisation window closes around week 9. Experiences between weeks 3 and 9 shape adult behaviour more than anything you do afterwards.
Use our cat age calculator for the human-age equivalent once the kitten is past month 2. Biological curves diverge from the "x7" myth sharply in the first year.

How We Built This Guide

This timeline pulls from four sources I trust and one I don't.

I trust the AAFP (American Association of Feline Practitioners) 2022 kitten care guidelines, the RSPCA UK neonatal kitten protocol, Cornell Feline Health Center's development reference, and Alley Cat Allies' field-tested foster timeline. Each of these agrees on the big beats — eyes open, weaning, first vaccine — and differs only at the edges.

The source I don't trust: Pinterest infographics. A scroll through "kitten milestones" pins turns up week numbers that contradict each other and gestational ages that are wrong by days. If you are learning kitten development from Pinterest, you are learning it wrong.

I fostered three litters between 2022 and 2024 with a local rescue and weighed every kitten daily with a kitchen scale. Numbers here come from that data as well as the published references. When the two disagree, I flag it.

Weeks 1 and 2: Eyes Closed, Ears Closed, Warm-Seeking

Weight: birth around 90-110 g. By end of week 1, around 150-180 g. By end of week 2, around 220-280 g.

What is happening:

Eyes and ears are still closed. A kitten this age navigates by smell, warmth, and touch. Picking it up gently does not distress it; it recognises you by how you smell and how warm you are.
Body temperature regulation is broken. Kittens cannot regulate their own body heat until around week 3. A heat source at 30-32°C (roughly human body temperature) is not a comfort thing, it is a survival thing. Without a mother, a covered heating pad set to low with a towel barrier is the standard foster setup.
They eat every 2-3 hours. This is real work for a foster carer. Mother-raised kittens will be feeding this often too; you just don't have to do it yourself.
Faecal and urinary stimulation is required. A mother cat licks the genital area to trigger elimination. For hand-reared kittens, a warm wet cotton ball does the same job. They cannot eliminate on their own yet.

By day 7 to 14, eyes start to open. They emerge blue-grey and unfocused; the kitten cannot really see yet, just detect light and shadow. Full focusing takes another 2-3 weeks.

Weeks 3 and 4: First Eye Contact, Soft Feet

Weight: by end of week 3, around 300-400 g. By end of week 4, around 400-550 g.

Week 3 is when the kitten becomes recognisably a small cat. Eyes are open, ears are open (the ear canals unfurl around day 10 and the kitten can locate sound by about day 14), and the first attempts at coordinated walking happen.

The feet at this stage are still soft. Claws are just starting to cycle through their first retraction reflex. Adult-cat climbing is weeks off; at week 3, kittens mostly stumble, topple, and get back up.

Week 4 milestones that matter:

First interest in solid food. If the mother is eating near the kittens, they will investigate her food. Offered food at this age should be soft: kitten kibble soaked to a porridge consistency, or wet kitten food mixed with a little kitten milk replacer. Hard dry food at week 4 almost always causes constipation.
Litter box introduction. A shallow tray with a small amount of unscented, low-dust litter. Kittens learn from watching the mother or from a quick after-meal introduction. Most kittens pick it up within a week.
Teeth start erupting. Needle-tiny incisors and canines. This is when biting and mouthing increases — and when the kitten is most receptive to being taught what is and is not a chewable target.

Weeks 5 and 6: Weaning, Play Fighting Starts

Weight: end of week 5, around 550-700 g. End of week 6, around 700-900 g.

Weaning is a transition, not an event. The rough pattern across weeks 4-6 looks like:

Week	Approximate diet split (milk : solid)	Feeding frequency
4	80 : 20	Every 4 hours
5	50 : 50	4-5 meals per day
6	20 : 80	4 meals per day
7	5 : 95	4 meals per day
8	Fully weaned	3-4 meals per day

Trying to compress this into two weeks usually produces loose stools, slower weight gain, and a more anxious kitten. Let the kitten set the pace.

Play-fighting with littermates kicks off around week 5. This is where kittens learn bite inhibition — the other kitten yelps and stops playing when bitten too hard, which teaches the biter a boundary that a human cannot teach as effectively. Single-kitten rescues without littermates need extra deliberate handling at this stage; they are the ones that grow up into adults who play-bite hard.

Weeks 7 and 8: The 1 kg Milestone, First Vet Visit

Weight: around 900 g-1.1 kg by end of week 8. The 1 kg mark is the conventional threshold for first vaccination and is generally the earliest safe age for rehoming, though most rescues wait until week 10-12.

At week 8 most kittens are fully weaned, using a litter box reliably, playing in coordinated bursts, and sleeping in 16-20 hour stretches across the day. First vaccinations are typically F3 (feline herpesvirus, calicivirus, panleukopenia) at 8 weeks, with a booster at 12 weeks.

This is also when many caretakers start thinking about insurance. Kitten policies are generally cheapest when signed up at 8-10 weeks because pre-existing conditions are limited to what is already documented. If you're working through whether a policy is worth it, our pet insurance math walkthrough covers how the break-even actually pencils out for cats in the first 2 years.

Weeks 9 to 12: Socialisation Window Closes

Weight: around 1.1 to 1.6 kg by end of week 12.

The sensitive socialisation period for cats runs roughly from week 3 to week 9. Between weeks 9 and 12 the window narrows and then closes. Experiences a kitten has — or doesn't have — during this window substantially shape adult behaviour.

Specifically, during weeks 3-9, positive exposure to:

Multiple gentle human handlers (5+ different people)
Normal household sounds (vacuum, doorbell, washing machine)
Being calmly held, brushed, having paws touched
A carrier that isn't associated only with vet trips

… tends to produce an adult cat that is less fearful, easier at the vet, and more tolerant of grooming and nail trims. Kittens that miss this window can still be socialised later, but it takes significantly more patience and often never fully closes the gap.

This is the single most leveraged thing you can do in kittenhood. Two weeks of calm handling now saves a decade of defensive behaviour later.

Weeks 13 to 16: Adolescence Begins

Weight: 1.6 to 2.2 kg. Large-breed kittens (Maine Coon, Ragdoll) run 10-20% above this.

Around week 13-14 the kitten transitions from dependent infant to independent adolescent. Energy rises sharply. Playtime gets rougher. Sleeping hours drop from ~18/day to ~14/day.

Key veterinary milestones:

Second vaccination booster around 12 weeks, with a third typically at 16 weeks.
Rabies vaccine typically first administered at 12-16 weeks depending on local law.
First deworming course complete by this stage. Most shelters deworm at 2, 4, 6, and 8 weeks; household kittens should follow a similar protocol with a vet.
Desexing conversations begin. Most vets now recommend early desexing at 4-5 months, before first heat; some prefer later at 6-8 months. Position varies by region and vet. The evidence base shifted toward earlier desexing in the 2020s but is not unanimous.

Weight Targets and When to Worry

A reasonable kitten weight gain is roughly 10-15 g per day through weeks 1-8. That is the benchmark I weigh against. Any 3-day stretch without weight gain, or any single-day weight drop of more than 5%, is worth a vet call.

Age	Healthy weight range	"Call the vet" threshold
Newborn	90-110 g	<80 g or not gaining by day 3
1 week	150-180 g	<140 g
2 weeks	220-280 g	<210 g
4 weeks	400-550 g	<380 g
6 weeks	700-900 g	<650 g
8 weeks	900 g-1.1 kg	<850 g
12 weeks	1.1-1.6 kg	<1.0 kg
16 weeks	1.6-2.2 kg	<1.5 kg

These ranges cover average-frame kittens. A Maine Coon kitten at week 12 can reasonably be 1.8-2.2 kg and still be on the lean side of normal for that breed. A very small-framed domestic shorthair at 1.0 kg at week 12 might still be within range. Context matters. Track the curve, not just the single number.

Red Flags: When "Not Normal" Means Vet Now

These are the ones I would not wait on:

Any kitten under 4 weeks old that won't nurse or bottle-feed for more than 4 hours. Hypoglycaemia and dehydration kill kittens this age within 12-24 hours.
Open-mouth breathing in any kitten at any age. Cats do not pant as a normal cooling mechanism. Open-mouth breathing signals respiratory distress.
Persistent diarrhoea >24 hours in a kitten under 8 weeks, or bloody diarrhoea at any age.
Eye discharge that glues the eyelids shut, especially before 3 weeks. Herpesvirus and conjunctivitis are common in neonates and can damage the cornea if untreated.
Cold to the touch in a kitten under 3 weeks. Hypothermia combined with their inability to self-regulate body temperature is an emergency.
No weight gain for 3 consecutive days at any age under 10 weeks.

A lot of kitten care is judgement calls between "normal variation" and "something is wrong." These six are the ones where I have learned not to wait and see.

FAQ

When do kitten eyes open?

Usually between day 7 and day 14. Some litters are at the early end, some at the late end; both are normal. If eyes are still closed past day 18, check with a vet — it can indicate infection under the eyelid or a developmental delay.

When should I start weaning?

Around week 4 to 5, when the kitten shows interest in the mother's food or in a wet-food mixture offered on a finger. Starting earlier than week 4 usually causes digestive upset; starting later than week 6 is fine and can be preferable for kittens that are small for their age.

How much should a 4-week-old kitten weigh?

Roughly 400-550 g is the typical range. Under 380 g is a vet-call threshold. Over 550 g is not a problem in itself but suggests checking body condition rather than just weight — some kittens are well-boned and appropriately heavy, others are over-conditioned from a rich formula.

Is there a kitten age calculator I can use?

For kittens under 3 months, go by the milestones and weight targets above — development is too fast for the standard age calculators to be useful at that granularity. From 3 months onward our cat age calculator uses the actual biological curve rather than the myth multiplier, so a 3-month-old kitten converts to roughly a 4-year-old human equivalent rather than 21.

Can I socialise a kitten after week 9?

Yes, but it is harder and slower. The neurological sensitive period closes around week 9-10; after that, new experiences register as more novel and potentially scary. Kittens socialised later can become well-adjusted adults but often retain specific fears (carrier, vacuum, strangers) that earlier-socialised kittens do not.

When is the first kitten vaccination?

Typically 8 weeks for the F3 (feline panleukopenia, herpesvirus, calicivirus). Boosters at 12 and 16 weeks. Rabies at 12-16 weeks. Local protocols vary; your vet will match the schedule to regional law and risk profile.

What is a safe temperature for newborn kittens?

Environmental temperature around 30-32°C for the first week, dropping gradually to 27-29°C by week 3-4 and room temperature (21-24°C) from week 4 onwards. Cold kittens do not feed; fed-but-cold kittens do not digest. Heat is arguably the single most important variable in the first 2 weeks.

Sources

American Association of Feline Practitioners (AAFP). 2022 feline life stage guidelines.
Cornell Feline Health Center. Kitten development reference, 2023 edition.
RSPCA UK. Neonatal kitten care protocol, 2024 revision.
Alley Cat Allies. Field guide to kitten fostering (6-week-by-week timeline).
WSAVA Global Nutrition Committee. Weaning and growth nutrition for cats.
Personal foster records, 3 litters, 14 kittens, 2022-2024.