Cat BMI Calculator

Human BMI is calculated from height and weight and works because human body proportions are relatively consistent. Cats vary enormously in body frame, breed, and muscle-to-fat ratio, making a height-weight index unreliable. The BCS system assesses fat cover and muscle condition directly through visual observation and touch, which is far more clinically accurate for cats.

Run your hands along both sides of your cat's ribcage with light pressure. At BCS 5 (ideal), you should feel the ribs easily - like the back of your hand - without seeing them. Then look at your cat from above: a clear waist should be visible behind the ribs. Finally, look from the side: a slight upward tuck of the abdomen is ideal. If ribs are invisible from across the room, your cat is likely overweight.

No more than 0.5-1% of current body weight per week, which for a 12 lb (5.4 kg) cat is about 1-2 oz (30-60 g) per week. Faster weight loss increases the risk of hepatic lipidosis, a potentially fatal fatty liver disease that can develop in overweight cats who cut calories too sharply or stop eating due to stress. Always work with a veterinarian for a supervised program.

Neutered and spayed cats have lower calorie maintenance needs - roughly 20-25% less than intact cats - but their ideal body composition (BCS 4-5) remains the same. The ideal weight target itself is based on body condition, not reproductive status. However, intact cats can typically eat somewhat more food without gaining weight.