Pet Weight Calculator

Weight management for pets comes down to comparing current daily calorie needs against target daily calorie needs, since the gap between the two is what drives the actual feeding change required to shift body weight over time. This calculator computes both figures independently in two steps: first a resting energy requirement (RER) -- roughly 30 calories per kilogram of body weight plus a flat 70-calorie baseline for dogs, or 70 times body weight in kilograms raised to the 0.75 power for cats (the standard allometric form, which stays smooth across the whole weight range instead of jumping at a cutoff) -- then a maintenance multiplier on top of that (1.6x for dogs, 1.2x for cats) to estimate typical adult maintenance calories, not just resting calories. Both formulas are applied once to current weight and once to target weight -- current weight only feeds current daily calories, and target weight only feeds target daily calories, so each calorie figure moves with just one of the two weight inputs, not both.

Weight to lose or gain is a straightforward subtraction of target from current weight: raising current weight (with target held fixed) increases how much needs to come off, while raising target weight (with current held fixed) shrinks that gap since the goal is now closer to where the pet already is. Percentage change expresses that same weight gap as a share of current weight, so it responds to both inputs but not always in an obviously symmetric way -- for example, raising current weight while target weight stays fixed increases both the absolute weight gap and the percentage figure together, since a bigger current weight makes the same fixed target look like a proportionally larger reduction. What this calculator doesn't account for: body condition score and where the pet currently sits relative to a genuinely healthy weight (which a formula alone can't tell you), individual variation in activity level, spay/neuter status, and breed (the 1.6x/1.2x multipliers are averages, not a substitute for a body-condition assessment), and safe rate of weight loss (crash dieting a pet is a real health risk, especially for cats -- see the FAQ below).