Enter your pet’s weight and pick their life stage, then the food you use. The calorie number on the bag or tin (kcal per 100 g, or per cup) makes the result far more accurate than the defaults.
For weight loss, enter your pet’s target weight, not their current weight.
Vets start from the resting energy requirement (RER) — the calories needed at rest: RER = 70 × (body weight in kg)0.75. That’s multiplied by a factor for life stage and activity to get the daily energy requirement. For a neutered adult dog the factor is about 1.6; for a neutered adult cat, about 1.2.
Example: a 20 kg neutered dog has RER = 70 × 200.75 ≈ 662 kcal, and needs about 662 × 1.6 ≈ 1,059 kcal a day. With 10% from treats, 953 kcal comes from food — about 258 g of a 370 kcal/100 g kibble, or 2.7 cups at 350 kcal a cup.
Calorie content varies a lot between foods, from about 300 to 450 kcal per 100 g for dry food and 70 to 130 for wet. It’s printed on the packaging (sometimes as kcal/kg — divide by 10 for per 100 g).
Roughly: RER = 70 × weight(kg)^0.75, times 1.6 for a typical neutered adult. A 10 kg dog needs about 630 kcal, a 20 kg dog about 1,060 and a 30 kg dog about 1,440 kcal a day. Divide by your food’s calories to get grams or cups.
A typical 4 kg neutered indoor cat needs about 240 kcal a day (RER × 1.2): around 60 g of dry food, or two to three 85 g pouches of wet food, depending on the brand.
Bag guides are deliberately generous averages for all dogs or cats of a weight. Neutered, indoor or less active pets often need 10–30% less. Use your pet’s body shape as the final guide.
Use your pet’s target weight and the weight-loss option, keep treats small, and aim to lose about 1–2% of body weight a week. Always plan weight loss with your vet, especially for cats.
Keep treats and snacks to about 10% of daily calories. This calculator takes that share off the food amount so the total stays the same.
