Dog and cat weight loss calculator
Feed for the target weight, not the current one: about 1.0 × RER at the target weight for dogs and 0.8 × RER for cats. A safe pace is 1 to 2% of body weight a week for dogs and 0.5 to 1% for cats, so losing 5 kg from a 30 kg dog takes roughly 10 to 19 weeks.
Free, no sign-up · Reviewed October 2026 · How it works
Pet
Ideally set by your vet. Not sure? Our body condition score check gives a rough target.
kcal per cup, from the bag. Weight-loss foods let pets eat more volume for fewer calories.
Daily calories for weight loss
783kcal
Including treats. About 2.2 cups a day of your food. To lose 5.0 kg.
Steady pace (1.0% a week)
19 weeks
by February 2027
Fastest safe pace (2% a week)
10 weeks
by December 2026
First weekly goal: lose about 0.3 kg to 0.6 kg.
Weigh every 2 weeks. If weight isn't moving after 4 weeks, cut calories by about 10% with your vet's advice. Check with your vet before starting, especially if your pet has a health condition.
For information only, not a diagnosis or a substitute for your vet. If your pet seems unwell or you're worried, call your vet.
How this tool works
The calculator works out the resting energy requirement (RER = 70 × weight in kg^0.75) at your pet's target weight and applies the AAHA 2021 weight-loss factor: 1.0 for dogs and 0.8 for cats.
It then estimates how long the loss will take at 1 to 2% of body weight per week for dogs and 0.5 to 1% for cats, within the 0.5 to 2% per week range used in veterinary weight-loss plans. Cats are kept to the slower end because rapid weight loss can cause a serious liver disease.
Plans need adjusting as you go: weigh every 2 weeks and, with your vet, cut by about 10% if your pet stops losing.
Questions.
How fast should my dog lose weight?
About 1 to 2% of body weight a week. For a 30 kg dog that's 300 to 600 g a week. Faster loss risks losing muscle and is hard to keep up.
How many calories should an overweight dog eat?
Roughly 1.0 × RER at the target weight. For a dog aiming for 25 kg, that's about 780 kcal a day, including treats.
Why can't cats lose weight quickly?
When cats eat too little, they can develop hepatic lipidosis (fatty liver), which can be fatal. Keep weight loss slow and supervised by your vet.
Related tools
- Is my dog or cat overweight? Body condition score checkPets don't have a BMI: vets use a 9-point body condition score.
- Dog and cat calorie calculatorHow many calories does your dog or cat need a day? Enter weight and life stage to get daily kcal using the vet RER formula and AAHA life stage factors.
- How much should I feed my dog or cat?Get daily cups or grams for your dog or cat from their weight, life stage and the calories in your food, plus the amount per meal.
- How much exercise does my dog need?Find your dog's daily exercise needs by breed type, age and health, from 20 minutes for flat-faced breeds to two hours or more for working dogs.
