How home-cooked portions are worked out

A home-cooked diet starts from the same calorie figure as any other diet: daily calories = RER × activity factor, where RER = 70 × (body weight in kg)^0.75. This calculator gives you that figure and converts it into a daily weight of cooked food, assuming roughly one kilocalorie per gram of cooked food — a reasonable average for a mix of lean meat, rice or potato, and vegetables. A ten-kilogram neutered adult dog needs about 630 kcal a day, which is about 630 grams of cooked food; a 4.5-kilogram neutered adult cat needs about 260 kcal, or about 260 grams. The calculator also shows a starting template by cooked weight: about forty percent lean protein, forty percent carbohydrate and twenty percent vegetables. That template is a way to visualise the portion, not a recipe — and the distinction matters enormously.

The template is not a balanced diet. A home-cooked diet made from meat, rice and vegetables, without a supplement, is deficient in calcium, zinc, iodine, vitamin E and vitamin D, and the calcium-to-phosphorus ratio will be wrong. Studies of home-cooked diets have repeatedly found that the great majority — in one well-known study, over ninety percent — are nutritionally incomplete when they are put together without veterinary guidance. The consequences are not theoretical: calcium deficiency causes fractures in puppies, iodine deficiency causes thyroid disease, and zinc deficiency causes skin disease. That is why this calculator is deliberately limited to portion size, and why the recipe itself must come from your vet or a board-certified veterinary nutritionist, with a proper vitamin and mineral balancer added.

Cats are not small dogs — especially at home

The warning is doubly important for cats. Cats are obligate carnivores: they need taurine, arginine and arachidonic acid from animal tissue, they cannot make vitamin A from plant sources, and they need a much higher proportion of protein than dogs. A home-cooked dog recipe fed to a cat will cause taurine deficiency, which leads to blindness and heart disease, and it can do so within months. A cat's home-cooked diet must be formulated for cats specifically, with the right protein level and the right supplements, and it must be checked regularly. If you are cooking for a cat, do not adapt a dog recipe — get a cat recipe from a veterinary nutritionist.

What affects the portion

Weight is the main input, and it should be the target weight if your pet is overweight. The activity factor matters as much as for any diet: a neutered adult dog uses 1.6, an intact adult 1.8, a puppy 2.0–3.0 and a senior 1.2; a neutered adult cat uses 1.2 and a kitten 2.0–2.5. The energy density of your own cooking matters too — the calculator assumes about one kilocalorie per gram, but a fatty meat or a lot of oil raises that, and a watery vegetable mix lowers it. The only way to know your own recipe's energy density is to work it out from the ingredients, which is another reason to have the recipe formulated professionally: the nutritionist will give you the calories per gram as part of the recipe, and you can use that figure instead of the assumption here.

Common mistakes

The most common mistake is cooking without a recipe — "chicken and rice" is not a diet, it is a bland meal, and feeding it for weeks causes deficiencies. The second is using a recipe from the internet or a book without checking it: most published home-cooked recipes have been found to be incomplete. The third is forgetting the supplement: a vitamin and mineral balancer is not optional, it is the part that makes the diet complete. The fourth is feeding the same recipe to a dog and a cat. The fifth is not weighing the food — home-cooked portions are even harder to eyeball than kibble, because the density varies with every batch. Weigh each meal on kitchen scales until you know what the portion looks like.

When to see a vet

Talk to your vet before starting a home-cooked diet, and have the recipe formulated by a veterinary nutritionist. See a vet promptly if your pet loses weight, has a dull coat, seems lethargic, has persistent diarrhoea, or shows any sign of illness on the new diet. Puppies, kittens, pregnant and nursing pets, and pets with kidney disease, diabetes or pancreatitis should never be put on a home-cooked diet without veterinary supervision — their nutritional needs are too specific and the risks of getting it wrong are too high. For the calorie figure behind the portion, use the dog calorie calculator or the cat calorie calculator; for the raw-food alternative, the raw food calculator.