Free Kitten Growth Estimate calculator with clear step-by-step results.
Healthy kittens gain roughly 100 grams a week for the first several months, so the ratio between actual and expected weight for age gives a growth index. That index is carried forward to the target age and capped at expected adult weight, since growth plateaus rather than continuing linearly.
Expected weight for age
Grams = 100 + age in weeks x 100, capped at adult weight
Projected weight
Projected = expected weight at target age x (current weight / expected weight now)
A rough growth guide only. Weight trends matter far more than a single reading, and any kitten failing to gain weight should be assessed by a veterinarian.
The kitten is lighter than typical for its age. That can be normal for a small breed or a large litter, but persistent slow gain warrants a veterinary check for parasites or underfeeding.
Most reach adult weight between nine and twelve months, though large breeds such as Maine Coons continue filling out until two to four years.