How old is my kitten?

Island of Cats · 2 October 2026 · 7 min read

Maybe a kitten turned up under your car. Maybe you took in a street cat and the vet asked how old it is. Either way, you can get surprisingly close by looking at a few things: eyes, ears, teeth, weight, and how it moves.

Kittens: what to look at

Eyes. Kittens are born with their eyes shut. They open over the first two weeks, and every kitten’s eyes start out blue. The adult colour starts coming in from about six or seven weeks. So blue eyes on a big, confident kitten don’t mean much, but a kitten with green or yellow eyes is very likely past two months.

Ears. Newborn ears are folded flat against the head. They unfold over the first couple of weeks and stand up by about three weeks, according to Alley Cat Allies’ week-by-week kitten guide.

Teeth. The most reliable clue. Kittens have no teeth at birth. The tiny front ones come in at two to four weeks and the baby premolars at five to six weeks, 26 baby teeth in all. The adult teeth usually start at around four months and there are 30 of them. If you can see big, white canines next to smaller baby ones, you’re looking at a kitten of about four to six months.

Walking and eating. Crawling at two weeks, wobbly walking at three, steady at four, running and pouncing by six. Kittens start trying solid food at around four weeks and are usually fully weaned by eight.

Weight. Useful if you have kitchen scales. A kitten roughly doubles its birth weight in the first week and reaches about a kilo at eight weeks. After that, a common shelter rule of thumb is about half a kilo for each month of age, up to around five months. Thin street kittens can weigh less than their age, so check the teeth too.

Grown cats: harder to tell

Once the adult teeth are in, a cat’s age becomes a guess. A vet can usually narrow it down, but these are the rough clues:

• Teeth. Young adults have clean white teeth. Tartar, wear and gum problems build up over the years, though diet makes a big difference.
• Eyes. From middle age, the lens of the eye often turns slightly hazy and blue-grey. It’s normal and doesn’t usually affect sight.
• Body and coat. Older cats lose muscle, especially along the spine and back legs, groom less and may grey around the face.

Vets group cats into four life stages: kitten up to one year, young adult from one to six, mature adult from seven to ten, and senior over ten. Seniors should see a vet every six months, the rest at least once a year.

Vaccines: when to start

Every cat, everywhere, should have the core vaccines. They protect against feline panleukopenia (a parvovirus that kills many kittens) and the two viruses behind most cat flu.

Under the World Small Animal Veterinary Association’s 2024 guidelines, kittens start at six to eight weeks, get a dose every three to four weeks until they’re at least sixteen weeks old, and then a booster at around six months. The last kitten dose has to be at sixteen weeks or later, because antibodies from the mother’s milk can block the vaccine before then.

After that, how often depends on the vaccine and on the cat’s life. Your vet may also suggest feline leukaemia (FeLV) for cats that go outside, and rabies where the law requires it or for travel.

A street kitten you’ve taken in should see a vet before it meets any cats you already have.

Worming and fleas

Kittens can pick up roundworms from their mother’s milk. The European parasite experts at ESCCAP recommend worming from three weeks old, every two weeks until two weeks after weaning, then monthly up to six months for kittens that go outside.

For fleas, always check the product’s minimum age and weight, because many aren’t safe for young kittens. And never use a dog flea treatment on a cat. Some contain permethrin, which is poisonous to cats.

Neutering: around four months

Female kittens can get pregnant from about four months old, so International Cat Care recommends neutering at around four months, before they can. Shelters and street cat programmes often neuter even earlier, from eight weeks and about a kilo, so kittens go to new homes already done. There’s more on why in our World Spay Day story.

Found a very young kitten on its own?

Don’t scoop it up straight away unless it’s in danger. The mother is often nearby, out finding food, and kittens do best with her. Watch from a distance for a few hours.

If she doesn’t come back, remember that kittens under about four weeks can’t keep themselves warm. Warmth comes first, then food. Never give cow’s milk, which upsets their stomachs. Use kitten formula from a vet or pet shop, and call a vet or a local cat rescue for help.

This guide is general information, not veterinary advice. Every kitten is different, and your vet can check its age and health properly.

Every cat you catch lands on the map, from the smallest kitten up.

Get the App →