A cat that gains a little weight in October is doing what the season tells it to do. A cat that gains more than 10 percent of its body weight between September and December is not storing fat for winter, it is becoming obese, and the extra 400 g on a 4 kg cat is the equivalent of 8 kg on a person. The difference between the two is arithmetic, not opinion.
Why autumn adds weight without extra food
Two things change at once. Daylight drops below 10 hours in most latitudes, and activity falls with it: outdoor cats come in earlier, indoor cats sleep more, and the 20 minutes of chasing a toy after dinner quietly disappears. At the same time, appetite rises. Many cats eat 10 to 15 percent more in cool weather, which is close to the size of the seasonal gain itself.
Cats also carry a genuine seasonal instinct to lay down fat, inherited from ancestors that faced winter prey shortages. The instinct is real; the shortage is not. A house cat with a full bowl in January is running a program that no longer has a purpose, which is why the weight stays on until spring.
Five to ten percent is the window
Weigh the cat now, at the start of the season, and write the number down. From that baseline, a rise of 5 to 10 percent by midwinter is acceptable in a cat that started at an ideal body condition. Above 10 percent is where the risk starts: at that point the cat is adding fat around the abdomen and inside the chest, and the pattern tends to continue into spring rather than reverse.
Weight alone is a blunt instrument, so score the body as well. Run your hands along the ribs: they should be easy to feel under a thin layer of fat, like the back of your hand. From above, there should be a waist behind the ribs; from the side, a tuck in front of the back legs. A cat at 5.5 kg with visible ribs and a waist is fine. A cat at 4.5 kg with no waist is not.
Do the calorie math once
Resting energy requirement is 70 x (body weight in kg to the power of 0.75). For a 4 kg cat that is about 198 kcal a day. A neutered indoor adult cat needs roughly 1.2 times that, so about 238 kcal a day. Inactive, older or already overweight cats sit closer to 1.0 times RER, which is 198 kcal, and a cat on a weight-loss plan is fed for its target weight, not its current weight.
Kilocalories mean nothing at the bowl, so convert. Dry food runs about 3.5 to 4.0 kcal per gram, close to 3.8 for most adult formulas, and a standard 85 g can of pate holds about 80 kcal. That puts a 4 kg cat at roughly 63 g of dry food, or 3 cans of pate, per day.
Weight to grams, at 1.2 times RER
| Weight | RER (kcal) | Daily target at 1.2 x | Dry food (3.8 kcal/g) | 85 g cans of pate |
|---|---|---|---|---|
| 3.0 kg | 160 | 191 kcal | 50 g | 2.4 cans |
| 3.5 kg | 179 | 215 kcal | 57 g | 2.7 cans |
| 4.0 kg | 198 | 238 kcal | 63 g | 3.0 cans |
| 4.5 kg | 216 | 260 kcal | 68 g | 3.2 cans |
| 5.0 kg | 234 | 281 kcal | 74 g | 3.5 cans |
| 6.0 kg | 268 | 322 kcal | 85 g | 4.0 cans |
The table is a starting point, not a verdict. Weigh food on a kitchen scale for 2 weeks: a measuring cup of dry food varies by 15 to 20 percent depending on how it is scooped, which is 40 to 60 kcal a day on a 4 kg cat. That is the size of the whole problem.
Where the extra calories actually come from
Rarely from meals. The usual sources are treats, shared human food and a second cat's bowl. Ten treats at 2 kcal each is 20 kcal, roughly 8 percent of a 4 kg cat's day, and free-feeding a bowl that is topped up before it empties adds an unknown amount on top. Count treats into the daily number, cap them at 10 percent of calories, and pick up the bowl between meals.
If two cats eat at different speeds, feed them in separate rooms for 15 minutes and take the bowls away. A cat that is losing weight while the other gains is often just slower at the bowl.
Weigh weekly, adjust in 2 percent steps
Use a baby scale or a kitchen scale with a box, same time of day, before the first meal. Weekly numbers are noisy, so compare 3-week averages. A healthy rate of loss is 1 to 2 percent of body weight per week: on a 5 kg cat, 50 to 100 g. Faster than that risks losing muscle and triggering hepatic lipidosis, which is a genuine emergency in cats.
If weight is climbing, cut the daily ration by 10 percent and hold it for 3 weeks before cutting again. Sudden cuts of 30 percent or more make cats frantic, cause crying at 4 a.m. and usually end with a broken plan. The full clinical picture, including when obesity becomes a disease rather than a number, is in obesity and weight loss, and a worked feeding schedule is in the weight loss feeding plan.
Six weeks from now
- Weigh the cat today and record the number, plus a body condition score from 1 to 9.
- Calculate RER at 70 x kg^0.75, multiply by 1.2, and convert to grams with the label's kcal per gram.
- Weigh the food on a scale for 2 weeks instead of using a cup.
- Cap treats at 10 percent of daily calories and move the bowl off the floor between meals.
- Re-weigh every week, compare 3-week averages, and adjust by 10 percent rather than by guesswork.
- If the cat is already 20 percent over ideal weight, book an exam before starting a diet: the food calculator gives a target, but a vet should confirm there is no other disease.
Frequently asked
How much autumn weight gain is normal for a cat?
A rise of 5 to 10 percent from the September weight is a normal seasonal shift in a cat that starts at an ideal body condition. Above 10 percent, fat is being laid down around the abdomen and inside the chest, and the gain usually persists into spring instead of reversing on its own.
How many calories does an indoor cat need per day?
Work out the resting energy requirement as 70 times body weight in kilograms to the power of 0.75, then multiply by 1.2 for a neutered indoor adult. A 4 kg cat lands near 238 kcal, which is about 63 g of dry food at 3.8 kcal per gram, or 3 cans of 85 g pate.
Should I cut my cat's food suddenly when it gains weight?
No. Cut the daily ration by 10 percent and hold it for 3 weeks before cutting again. Losing faster than 1 to 2 percent of body weight a week risks muscle loss and hepatic lipidosis, and a sudden 30 percent cut usually ends with a hungry cat crying at night and an abandoned plan.