Method and practical guidance
For healthy dogs and cats, resting energy requirement (RER) is 70 × (body weight in kg)^0.75 kcal/day. One factor gives an initial daily maintenance energy requirement (MER): the Merck Veterinary Manual table gives adult dogs 1.6 × RER when neutered or 1.8 when intact; cats 1.2 or 1.4; puppies under 4 months 3 and older puppies 2; kittens 2.5. Young animals use a growth factor instead of an adult neuter or activity factor. Sedentary uses Merck’s obesity-prone starting factors (dog 1.4, cat 1.0). For active dogs, we use the PetMD light-exercise factor of 2 × RER, not a stacked activity adjustment; moderate and heavy exercise in that veterinary guide have substantially higher factors and require individualized guidance. No standardized active-cat factor is applied: an active cat displays the adult reproductive-status baseline, so ask your veterinarian to tailor it. Senior animals retain the adult baseline: age alone does not justify automatically reducing calories. Monitor body condition score (BCS), weight and actual activity, then adjust with your veterinarian.
For adult horses of 200–600 kg, this tool estimates maintenance digestible energy (DE) = 1.4 + 0.03 × kg Mcal/day, a formula described by Kentucky Equine Research, with indicative light/moderate/heavy workload factors 1.2/1.4/1.6. The Merck equine nutrition chapter discusses NRC workload guidelines and 20%, 40%, and 60% increases over maintenance. Horse DE in Mcal/day is not the same metric as dog/cat MER in kcal/day; 1 Mcal = 1,000 kcal, but a feed mass cannot be inferred without its DE density. Merck recommends roughly 1.5–2% of body weight as forage dry matter daily; this is a separate forage-intake guideline, not a percentage of the energy result.
These figures are starting estimates, not feeding prescriptions for pregnancy, lactation, obesity treatment, disease, or growing horses. Treats count toward daily intake; feed labels supply energy density needed to translate a target into portions. Ask a veterinarian or equine nutritionist about changes to diet or body condition. For related planning see the Pet Gestation Calculator, Pet Age Calculator, and Dog Size Predictor.
Frequently asked questions
Is RER the amount I should feed?
No. RER is resting energy, while an estimated daily MER uses one life-stage or adult factor. Individual needs vary with body condition and health.
Do seniors always need fewer calories?
No. Senior needs vary. This estimate starts at the adult factor and should be adjusted based on body condition, muscle and veterinarian guidance.
Does the horse result tell me how many kilograms of feed to give?
No. Horse digestible energy is in Mcal/day. Feed amounts depend on the dry-matter content and digestible-energy density of the actual ration.