How do you help a cat gain weight safely? Slowly, with a little more of a complete and balanced food, split into more meals a day, and a monthly weigh-in — and, first, a vet check to find out why the cat is underweight. A cat that is underweight because it is not getting enough food needs more food; a cat that is underweight because it is ill needs a vet, not just more food. This guide covers the difference, the feeding plan, and the mistakes to avoid. Every figure is an estimate, and a cat that is losing weight, or that has lost weight fast, should be seen by a vet promptly.
The short version is: see a vet first if the cat is losing weight, is off its food, is lethargic, or is a senior or a young animal that is not growing. If the vet says the cat simply needs more food, feed about 10% more than the normal amount, split into two or three meals a day, and re-weigh in a month. Aim for slow, steady gain — a few hundred grams a month for a dog, a little less for a cat — and keep the food measured, so you know what is working. The cat ideal weight calculator works out a target weight range, and the underweight cat signs and what to do guide lists the signs to watch for.
Why is my cat underweight?
An underweight cat is sometimes simply not getting enough food: a young animal growing fast, a nursing mother, or a very active cat can all need more than they are given, and a cat that is fed by eye rather than by measure can be underfed without anyone noticing. A cat that has recently changed homes, or that is stressed by a move or a new pet, may eat less for a while. Those causes are fixed by more food, fed little and often, and a calm routine.
But weight loss in a cat that is eating normally is a warning sign, and it needs a vet to find the cause. Dental pain, parasites, thyroid problems, kidney disease, diabetes, and some other conditions all cause weight loss, and they need treating, not just more food. An older cat that is losing weight needs a vet check promptly, because weight loss in a senior cat is never normal on its own. A young animal that is not gaining weight needs a vet check too, because a kitten that is not growing needs a vet, not just more food. The senior cat weight loss causes guide covers weight loss in older cats, and the kitten too skinny — what to do guide covers young animals.
How many calories does a cat need to gain weight?
Start with the resting energy requirement, or RER — the calories a cat burns at rest. The formula vets use is: RER equals 70 times body weight in kg to the power of 0.75. A typical neutered adult cat needs about 1.2 times its RER, and a cat that needs to gain weight usually needs about 10 to 20% more than its normal maintenance amount as a starting point — about 1.4 times its RER. The table below gives the daily calories for a cat at different weights, at the normal adult factor and at the weight-gain target. Use the row nearest the cat's current weight.
| 2 kg | 140 | 165 | | 3 kg | 190 | 225 | | 4 kg | 240 | 275 | | 5 kg | 280 | 330 | | 6 kg | 320 | 375 |
If weight is not moving after a month, add about 10% more food and re-weigh in another month. If the cat is eating well and still losing weight, or if it has gone off its food, see a vet promptly rather than feeding more. Note that calories are the real target and cups are only a translation: different foods have very different calorie densities, so always check the kcal per cup or per 100 g on your own bag or tin and work from that. The cat calorie calculator works out the same figures for any weight.
Feeding a cat that needs to gain weight
Feed a complete and balanced food, measured with scales or a measuring cup, split into two or three meals a day rather than one large meal — a cat that needs to gain weight often has a small appetite, and smaller meals more often are easier to eat than one large meal. A kitten food, or a food made for active cats, can help, because it carries more calories per mouthful — but only with your vet's agreement, and only if the cat is otherwise healthy. Do not add fatty scraps, gravy, or oil to the food: fat upsets the stomach, and a cat with an upset stomach eats less, not more.
Keep treats sensible: a few small treats are fine, but treats should not replace meals, and a cat that fills up on treats will not eat its proper food. Feed in a quiet place, at the same times every day, and take the bowl away after twenty minutes so the cat learns that food comes at meal times. If there are other pets in the house, feed the underweight cat separately, so it is not pushed away from its bowl. The how much food should a kitten eat guide gives the calorie tables for growing cats, and the feeding a nursing cat guide covers the time when a cat needs the most food of all.
How fast should a cat gain weight?
Slowly. A cat that gains weight fast is gaining fat, not muscle, and a cat that is fed a lot more all at once can get an upset stomach. Aim for a few hundred grams a month for a dog, and a little less for a cat, re-weighed monthly. Weigh the cat monthly, at the same time of day, on the same scales, and write the number down — the line over months is what matters, not any single reading. Feel the ribs at every weigh-in too: you should be able to feel them easily under a thin layer of fat, and see a waist from above and from the side.
A cat that is gaining weight but still has ribs that are easy to see is still underweight, and a cat whose ribs are hard to feel and whose waist has gone has gone too far. The cat body condition score chart gives the full nine-point scale, from 1 (emaciated) to 9 (obese), with 4 to 5 as the ideal range. If the cat is not gaining weight after two months of more food, or if it is losing weight despite eating well, see a vet — a cat that does not gain weight on more food needs a vet check, not more food.
Mistakes to avoid
The most common mistake is feeding a lot more all at once: a cat that is suddenly given much more food can get an upset stomach, and a cat with an upset stomach eats less, not more. Add about 10% at a time, wait a month, and then decide. The second is feeding fatty scraps and gravy: fat upsets the stomach, and a cat that is fed scraps will fill up on scraps and not eat its proper food. The third is changing food every few weeks: a weight-gain plan needs at least two months before it can be judged, and a food changed after two weeks has not had a fair trial.
The fourth mistake is skipping the vet check: a cat that is losing weight without a change in food, or that is not gaining weight on more food, needs a vet, not just more food — dental pain, parasites, thyroid problems, kidney disease, and diabetes all cause weight loss, and they need treating. The fifth is forgetting exercise: a cat that gains weight without moving will gain fat, not muscle, so keep exercise regular but gentle — short, frequent walks or play sessions, every day. The best exercise for overweight cats guide is written for heavy cats, but the same gradual build-up applies to a cat gaining weight.
For related reading, see the cat ideal weight calculator, the underweight cat signs and what to do guide, the cat body condition score chart, the how to weigh your cat at home guide, the senior cat weight loss causes guide, the cat calorie calculator.
Frequently asked questions
How do I help my cat gain weight safely?
Slowly, with a little more of a complete and balanced food, split into two or three meals a day, and a monthly weigh-in. Feed about 10% more than the normal amount, re-weigh in a month, and aim for slow, steady gain. See a vet first if the cat is losing weight, is off its food, is lethargic, or is a senior or a young animal that is not growing.
How many calories does my cat need to gain weight?
As a starting point, about 10 to 20% more than its normal maintenance amount — about 1.4 times its resting energy requirement (RER), where RER equals 70 times body weight in kg to the power of 0.75. A cat of 3 kg needs about 225 calories a day to gain weight, against about 190 at normal maintenance.
Why is my cat losing weight even though it eats well?
Weight loss in a cat that is eating normally is a warning sign: dental pain, parasites, thyroid problems, kidney disease, diabetes, and some other conditions all cause weight loss, and they need a vet to find them. See a vet promptly rather than feeding more — a cat that does not gain weight on more food needs a vet check, not more food.
Should I feed my cat more treats to help it gain weight?
No — treats should not replace meals, and a cat that fills up on treats will not eat its proper food. Keep treats sensible, feed a complete and balanced food in measured amounts, and split it into two or three meals a day. Do not add fatty scraps or gravy: fat upsets the stomach, and a cat with an upset stomach eats less, not more.
How fast should my cat gain weight?
Slowly — a few hundred grams a month for a dog, and a little less for a cat. A cat that gains weight fast is gaining fat, not muscle. Weigh monthly, feel the ribs at every weigh-in, and check the body condition score, where 4 to 5 is ideal.
When should an underweight cat see a vet?
See a vet promptly if the cat is losing weight without a change in food, if it is lethargic or off its food, if it is a senior, if it is a young animal that is not growing, or if it is not gaining weight after two months of more food. Bring the weight record and the food details.
Results on this page are estimates for general information only and are not veterinary advice. If your pet is ill, underweight, overweight, pregnant, or has a health condition, consult your veterinarian before changing diet or care.