Kitten Age Calculator
How old is your kitten? If you found it or took it in, nobody can tell you its birth date — but its weight puts it close. The estimate below comes from a published study of shelter kittens, and it comes with the accuracy the authors measured themselves.
Estimated age
4 weeks
about 4 weeks old — for a kitten of 16 oz.
Inside the range where the study found weight a good guide to age.
A kitchen scale works. 16 oz is one pound — weigh the kitten before a feed rather than after, and use the same scale each time so the trend means something.
How to tell how old a kitten is
Weight is the easiest measure to take, and DiGangi et al. (2019) tested exactly how well it works. Their answer is encouraging early and blunt later: accuracy to within one week ran at 98.8% at two weeks of age and fell to 17.9% by 20 weeks. That is why this page stops promising precision after about 10 weeks rather than printing a confident number anyway.
What the eyes and teeth say
Past the point where the scale stops helping, development does. ASPCA Pro publishes the markers shelters use: eyes are closed in the first week and opening in the second; they are open with a blue cast through weeks three and four, changing colour through weeks five and six, and at their adult colour by weeks seven and eight. Teeth follow their own order — none at all for the first two weeks, then the baby incisors around week three, the canines around week four, the lower premolars around week five and the upper ones around week six, with a full set of baby teeth by weeks seven and eight.
ASPCA Pro also notes that a normal kitten gains 7–15 g a day, and says plainly that weight should be used together with those milestones rather than on its own. Read both, and let the one you can see most clearly lead.
Where the two sources disagree
They very nearly don’t, which is worth saying. At two weeks DiGangi et al. put the average kitten at 11 oz, while the top of the ASPCA range for that week is 295 g — a gap of 1.7%. Two organisations, two populations, two methods, and they land within a rounding error of each other. We show the gap rather than averaging it away.
Common questions
How old is my kitten?
Weigh it, and read the estimate above. It comes from DiGangi et al. (2019), who weighed shelter kittens from newborn to 20 weeks and published the average weight at each age. The estimate is good early and loose later: the authors measured accuracy to within one week at 98.8% at two weeks of age, falling to 17.9% by 20 weeks. Past about 10 weeks, teeth and eye colour tell you more than the scale does.
How to tell how old a kitten is without weighing it?
Look at the eyes and the teeth. ASPCA Pro publishes the markers shelters use: eyes closed in the first week, opening in the second, open with a blue cast in weeks three and four, changing colour in weeks five and six, and adult colour by weeks seven and eight. Teeth arrive in order — none for two weeks, baby incisors around week three, canines around week four, lower premolars around week five, upper premolars around week six, a full set of baby teeth by weeks seven and eight.
Why does this stop at 20 weeks?
Because that is where the data stops. DiGangi et al. weighed kittens up to 20 weeks and no further, so extending the curve past that would mean inventing numbers. If your kitten weighs more than the chart covers, it is simply older than the study followed.
My kitten weighs less than others its age — is something wrong?
Not necessarily, and one weighing tells you little either way. ASPCA Pro notes that a normal kitten gains 7–15 g a day, so the direction of travel across several days matters far more than a single figure. A kitten that stops gaining, or loses weight, should be seen by a veterinarian rather than measured again.
Do the two sources agree?
Almost exactly, which is worth knowing. At two weeks DiGangi et al. put the average kitten at 300 g; the top of the ASPCA range for that week is 295 g — a difference of 1.7%. Two organisations, two populations, two methods, landing within a rounding error of each other. We show the gap rather than averaging it away.
Will this tell me how big my cat will get?
No. This estimates age from weight while a kitten is growing; it says nothing about adult size. No published study supports predicting an individual cat's adult weight from an early weight, so this site does not claim to.
Weight alone gives an estimate, not a birth date, and it stops being a reliable guide after about ten weeks. Teeth and eye colour tell you more from then on. A veterinarian can date a kitten far better than any calculator.
Verified on . Based on Assessment of body weight for age determination in kittens (DiGangi et al., Journal of Feline Medicine and Surgery, 2019 (tables 1 and 2, weight-for-age, male and female)) and Kitten Age & Weight Chart (ASPCA Pro, 2023 (golden-test source, not used to build the calculation)). See the method.