Kitten Growth Chart — Weight by Age, Predicted Adult Weight, and Development Milestones

In 2026, a kitten foster volunteer in Birmingham weighs three orphaned 2-week-old Domestic Shorthair kittens on a digital kitchen scale and finds one of them is 130 g lighter than its littermates — below the 85% healthy band on the breed growth curve. The runt-of-litter pattern is well-known to foster networks, but knowing when to intervene clinically vs when to assume it's a normal litter-rank effect requires real curve reference data. This calculator exists because that decision — to feed-supplement, to call the vet, to assume normal — happens dozens of times per day in foster networks worldwide, and the curve reference is the single most useful piece of data.

The growth-curve reference data in this tool comes from three sources. The first is Royal Canin's breed-specific growth research, published in their veterinary diet documentation and updated approximately annually for the major CFA breeds. The second is Hill's Science Diet large-breed growth research, particularly the Maine Coon and Ragdoll late-maturation curves. The third is the Cornell Feline Health Center kitten-medicine archive, which tracks growth trajectories across mixed-breed shelter and foster populations. These three sources converge on a consistent picture: breed-specific anchor points at birth, 4 weeks, 3 months, 6 months, and 12 months, with linear interpolation between as a reasonable working model.

Milestone markers come from Cornell's developmental biology archive and the AAFP Kitten Care Guidelines (2020). Eyes open between days 7 and 14 with a target window of day 10. Weaning starts at 4 weeks and completes by 8 weeks — never separate a kitten from its queen before 8 weeks because the social learning that occurs in this window is irreplaceable. The FVRCP vaccine series at 6/9/12 weeks reflects ACVIM consensus on maternal-antibody decay curves: vaccinating earlier than 6 weeks risks interference from maternal antibodies still present; vaccinating later than 12 weeks risks the immunity-gap window where the kitten is no longer protected by mom but not yet protected by vaccine. The 4–6 month neuter window represents a compromise between early-age neuter safety data (proven down to 8 weeks / 1 kg minimum in shelter-medicine research) and most private vets' preference for fully-developed surgical anatomy.

The healthy band of 85–115% is empirically derived from clinical experience: kittens within this band rarely warrant intervention; kittens below 85% benefit from feeding adjustment and a parasite check; kittens below 70% need vet workup within 24–48 hours because the differential includes serious causes (congenital cardiac defects, inadequate milk supply in large litters, viral infections, severe intestinal parasitism). Kittens above 115% are usually fine — kittens can be plump — but consistent over-tracking, especially in cobby breeds (British Shorthair, Persian), warrants portion control before adult obesity sets in.

Breed-specific differences in growth velocity are striking. A Siamese reaches adult weight at 12 months; a Maine Coon takes 36 months. Both are normal trajectories for the breed but would represent gross under-growth and gross over-feeding respectively if you applied the wrong curve. Royal Canin's breed research shows that feeding a Maine Coon kitten on a small-breed growth curve under-feeds them and risks skeletal mineralization deficits in adults; feeding a Siamese kitten on a Maine Coon curve over-feeds them and accelerates the adult obesity loading curve. The per-breed curves in this tool exist specifically to keep the right kitten on the right curve.

For the calorie math behind feeding plans, see cat calorie calculator; for portion-mix planning, see cat food calculator; for body-condition assessment, see cat BCS calculator. Last reviewed: 2026-05.