Estimating the calorie need
Body weight in kilograms drives the base figure: resting energy requirement (RER) is 70 x kg^0.75. A life-stage multiplier turns that into maintenance energy requirement (MER): roughly 1.6 for a neutered adult, 1.8 for an intact adult, 2.0 to 3.0 for growing puppies and kittens, and about 1.0 for weight loss. Age and activity do not change the base formula; they only change the multiplier applied to it.