Is your cat at a healthy weight?

Over half of pet cats are overweight, and — as with dogs — most owners do not realise it. Cats gain weight gradually, a few grams a week, and a long-haired cat can hide a kilogram of fat under its coat. This calculator gives you two checks: the typical adult weight range for your cat's breed, from the published breed standard where one exists, and the body condition score (BCS), the nine-point scale your vet uses, where five is ideal. It combines them into an estimated ideal weight, using the rule that each BCS point is roughly ten to fifteen percent of body weight. If the two checks agree, you can be confident; if they disagree, trust the BCS — it accounts for your cat's build, muscle and coat in a way the scale cannot.

The breed range is wide. A Persian's typical adult weight is three to six kilograms, a Maine Coon's is six to eleven — and a domestic shorthair, the most common cat of all, can be healthy anywhere from three to six kilograms depending on its frame. That is why the calculator shows a range and a midpoint rather than a single number. A cat inside its breed range with a BCS of five is almost certainly fine. A cat above the range with a BCS of seven is overweight. A cat above the range with a BCS of five is simply a large example of its breed — Maine Coons in particular are often mistaken for overweight cats by owners who have only ever had smaller cats.

The body condition score for cats

Feel the ribs with flat fingers: at BCS five you can feel them easily under a thin layer of fat, without pressing hard. If you have to press, your cat is probably a six or seven; if you cannot feel them at all, it is an eight or nine. If the ribs are prominent and there is no fat cover, it is a three or four. Look from above: at an ideal weight you can see a waist behind the ribs. Look from the side: the belly tucks up. Cats also carry fat in a pouch under the belly — the primordial pouch — which is normal in many cats and is not the same as obesity; the ribs and the waist are the reliable signs, not the pouch. The calculator asks you to pick the BCS that matches what you feel, and estimates the ideal weight from it.

The one warning that matters most

Cats must never lose weight fast. Rapid weight loss in cats can trigger hepatic lipidosis, or fatty liver disease, in which fat floods the liver and the liver fails. It is life-threatening, it can develop after only two days without food, and overweight cats are at the highest risk — which creates a cruel trap: the cats that most need to lose weight are the ones most at risk from losing it too fast. A safe rate for a cat is under one percent of body weight per week, and any weight-loss plan for a cat must be vet-supervised, with the food measured and the weight checked regularly. Never starve a cat, never cut its food by half overnight, and never assume that a cat that stops eating is on a hunger strike — a cat that has not eaten for twenty-four to forty-eight hours needs a vet urgently.

What affects the result

Breed sets the range, but sex, age and build shift the target: males are usually heavier than females, and large breeds such as Maine Coons and Norwegian Forest Cats keep growing until eighteen months or later. Neutering lowers calorie needs by twenty to thirty percent and is the most common trigger for weight gain — the risk is highest in the months after the operation. Indoor cats gain weight more easily than outdoor cats because they move less, and older cats gain weight more easily because their metabolism slows. Some breeds, such as British Shorthairs, are prone to weight gain, while others, such as Siamese and Abyssinians, are naturally lean.

Common mistakes

Free-feeding dry food is the biggest mistake — a bowl that is always full is an open invitation to overeat. The second is judging weight by looking rather than feeling, which a thick coat defeats. The third is crash dieting, which risks fatty liver disease. The fourth is using the breed range as a single target and ignoring the BCS. The fifth is forgetting treats, which can be a quarter of a small cat's daily calories. The sixth is feeding dog food, which lacks taurine and vitamin A and will cause serious deficiency within weeks.

When to see a vet

See your vet if your cat is more than twenty percent above its ideal weight, is losing weight without trying, or has a BCS of eight or nine — and see a vet urgently if your cat stops eating. Sudden weight loss can be an early sign of kidney disease, hyperthyroidism, diabetes or cancer. If your cat is overweight, ask your vet to set a target weight and a calorie plan, and to check for the conditions that make weight loss harder. Use the cat calorie calculator for the daily calories at the target weight, the cat food calculator for the food amount, and the feeding schedule generator for mealtimes. Re-weigh monthly and keep a record.