# Kitten Age Calculator

How old is my kitten? Weigh it: this estimates a kitten's age from its body weight, using DiGangi et al. (2019), who weighed shelter kittens from newborn to 20 weeks.

## How accurate it is, measured by the authors

Accuracy to within one week ran at 98.8% at two weeks of age and fell to 17.9% by 20 weeks. Past about 10 weeks, weight alone often over- or underestimates age, and teeth and eye colour tell you more. The chart stops at 20 weeks because the data does — we do not extend a curve past its measurements.

## What the eyes and teeth say (ASPCA Pro)

Eyes: closed in week one, opening in week two, open with a blue cast in weeks three and four, changing colour in weeks five and six, adult colour by weeks seven and eight. Teeth: none for the first 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. ASPCA Pro also notes a normal kitten gains 7-15 g a day, and says weight should be used together with these milestones rather than on its own.

## Where the two sources disagree

Almost nowhere. 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 gap 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.

## 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.

## Sources

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- Wikidata — cat breed mass (property P2067) — Wikimedia Foundation, query run 2026-07-28, CC0 license (https://query.wikidata.org/)
- Breed weights — official AKC breed standards — American Kennel Club, breed pages, accessed 2026-07-29 (https://www.akc.org/dog-breeds/)
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- Growth standard charts for monitoring bodyweight in dogs of different sizes — Salt et al., PLoS ONE, 2017, vol. 12, no. 9, e0182064 (correction 2024: data availability only) (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0182064)
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- Effect of diphenhydramine and cetirizine on immediate and late-phase cutaneous allergic reactions in healthy dogs — Papich et al., Veterinary Dermatology, randomized, double-blinded crossover study, 12 dogs (abstract, PMID 31899570) (https://pubmed.ncbi.nlm.nih.gov/31899570/)
- Approximate Gestation Periods — gestation length in the bitch and the queen — Merck Veterinary Manual, “Approximate Gestation Periods” table, accessed 2026-07-30 (https://www.merckvetmanual.com/multimedia/table/approximate-gestation-periods)
- Dystocia in Small Animals — Merck Veterinary Manual, “Diagnosis of Dystocia in Small Animals” section, accessed 2026-07-28 (https://www.merckvetmanual.com/reproductive-system/reproductive-diseases-of-the-female-small-animal/dystocia-in-small-animals)
- Factors affecting gestation duration in the bitch — Eilts et al., Theriogenology, 2005, vol. 64, no. 2, p. 242–251 (https://pubmed.ncbi.nlm.nih.gov/15955350/)
- Nutritional Requirements of Small Animals — energy requirements of the dog and cat — Merck Veterinary Manual, “Energy” section, accessed 2026-07-23 (https://www.merckvetmanual.com/management-and-nutrition/nutrition-small-animals/nutritional-requirements-of-small-animals)
- Chocolate Toxicosis in Animals — Merck Veterinary Manual, “Methylxanthine Content of Various Types of Chocolate” table and “Etiology” section, accessed 2026-07-28 (https://www.merckvetmanual.com/toxicology/food-hazards/chocolate-toxicosis-in-animals)
- ASPCA Poison Control — ASPCA, 24-hour emergency line, accessed 2026-07-28 (https://www.aspca.org/pet-care/aspca-poison-control)
- Cat pregnancy — how long pregnancy lasts in cats — International Cat Care, accessed 2026-07-30 (golden-test source, not used to build the calculation) (https://icatcare.org/articles/cat-pregnancy)
- Estrous length, pregnancy rate, gestation and parturition lengths, litter size, and juvenile mortality in the domestic cat — Root et al., Journal of the American Animal Hospital Association, 1995, vol. 31, no. 5, p. 429–433 (golden-test source, not used to build the calculation) (https://pubmed.ncbi.nlm.nih.gov/8542362/)
- How old is your cat? — life stage and human equivalent age — International Cat Care (Cat Friendly Clinic), accessed 2026-07-28 (https://icatcare.org/resources/cat-friendly-clinic/how-old-is-your-cat-handout.pdf)
- The Special Needs of the Senior Cat — cat age in human years — Cornell Feline Health Center, Cornell University, accessed 2026-07-28 (golden-test source, not used to build the calculation) (https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/special-needs-senior-cat)
- Calorie Needs for an Average Healthy Adult Cat in Ideal Body Condition — WSAVA Global Nutrition Committee, updated July 2020 (golden-test source, not used to build the calculation) (https://wsava.org/wp-content/uploads/2020/07/Calorie-Needs-for-Healthy-Adult-Cats-updated-July-2020.pdf)
- 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) (https://doi.org/10.1177/1098612X19844846)
- Kitten Age & Weight Chart — ASPCA Pro, 2023 (golden-test source, not used to build the calculation) (https://www.aspcapro.org/sites/default/files/2023-08/aspca_kittenchart_2023.pdf)

Full method: https://petmeasure.com/sources

_Verified 2026-07-28. Estimates only — this does not replace veterinary advice._