Why weight matters for pets
Overweight is the most common nutritional problem in dogs and cats. In a 2022 survey, the Association for Pet Obesity Prevention estimated that 59% of US dogs and 61% of US cats were overweight or obese. Excess weight shortens life, and raises the risk of arthritis, diabetes, breathing problems and, in cats, urinary disease. A long-term study of Labrador retrievers found that dogs kept lean lived about two years longer than their littermates.
The body condition score
Weight alone does not say whether a pet is fat, because breeds and individuals differ so much. Veterinarians use a body condition score (BCS) from 1 to 9, developed by Dorothy Laflamme in 1997:
| Score | Description |
|---|---|
| 1 to 3 | too thin: ribs, spine and hip bones easily felt or visible |
| 4 to 5 | ideal: ribs felt under a slight fat cover, waist visible from above, belly tucked up |
| 6 to 7 | overweight: ribs harder to feel, waist barely visible |
| 8 to 9 | obese: ribs hard to feel under heavy fat, no waist, fat on the back and base of the tail |
Estimating ideal weight
Each point above 5 corresponds to roughly 10% excess weight. The calculator uses:
Ideal weight = current weight ÷ (1 + 0.1 × (BCS − 5))
Example
A 55-pound dog with a score of 7 is about 20% overweight: its ideal weight is about 46 pounds, so it should lose about 9 pounds. At 1.5% of body weight per week, that takes about 12 weeks.
Calories for weight loss
The calculator estimates the resting energy requirement at the ideal weight, 70 × (ideal weight in kg)^0.75 kcal per day, and uses it as the daily target for a dog, or 80% of it for a cat. This is a starting point; your vet will adjust it after weighing your pet every 2 to 4 weeks.
Safe weight loss
- Aim for 1 to 2% of body weight per week for dogs, 0.5 to 1% for cats.
- Never starve a cat: fasting can trigger hepatic lipidosis, a serious liver disease.
- Weigh the food with a kitchen scale rather than using a cup.
- Count treats and table scraps, which should stay under 10% of daily calories.
- Increase activity gradually with walks and play.
Limits
The 10% per point rule is an approximation, less reliable for very obese animals. Weight loss diets should be supervised by a veterinarian, especially for pets with health problems, puppies, kittens and pregnant animals.