Weigh the cat once a month through autumn, on the same scale, to 5 grams, at the same hour, and compare each number with the September baseline rather than with last week. A drift of 5 percent in either direction is the alarm line. Gaining 3 to 5 percent before winter is normal reserve; gaining more than 10 percent is the start of an obesity problem that will be much harder to fix in February.
Once a month, same hour, same scale
Monthly is the right cadence for an adult cat because a cat's weight moves slowly and daily noise is large. Fix the date, ideally the first Sunday of the month, and the hour, between 06:00 and 08:00 before the first meal. One month is roughly 30 days, which is long enough for a real trend and short enough to catch a 5 percent slide before it becomes 10. Write the number on a paper taped inside a kitchen cabinet; an app works too, as long as it graphs.
Why 5 grams of resolution is the minimum
A 5 percent change on a 4 kg cat is 200 grams, which sounds easy to see, but the useful early signal is a 100 to 150 gram move, and a scale that rounds to 50 grams hides half of that. Use a digital scale with 5 gram or better resolution, tare a towel or shallow box, and take the reading twice. Check the scale with a 2 kg weight once a season; a scale that reads 1.5 percent high turns a normal cat into an alarm and a real 5 percent loss into nothing.
What moves the number before the cat does
Meal timing is the largest error source: a cat weighed 30 minutes after a 60 gram meal reads 40 to 60 grams heavy. A full bladder adds 20 to 40 grams, a full colon another 30 to 50. Weigh after the morning litter box visit, before food, and on the same spot on the floor, since a soft rug can shift a reading by 10 to 20 grams. In autumn, a thick winter coat does not add grams on the scale, but owners read a fluffier cat as a fatter cat and skip the check that would have caught the real change.
The plus or minus 5 percent rule
Three bands make the number actionable. Within 5 percent of baseline, log it and keep going. Between 5 and 8 percent, reweigh in 14 days and count calories for 7 days; a 200 gram drop on a 4 kg cat is 5 percent and deserves a reason. Above 8 percent, or any 5 percent change that comes with more drinking, more urination, vomiting, or a dull coat, book a vet visit within 7 days. Direction matters as much as size: a 5 percent loss over 3 months is slower and often more serious than the same loss over 3 weeks.
Baselines and both alarm lines
| September weight | Winter reserve ceiling, plus 5 percent | Alarm line, minus 5 percent | Vet line, minus 8 percent |
|---|---|---|---|
| 3.0 kg | 3.15 kg | 2.85 kg | 2.76 kg |
| 4.0 kg | 4.20 kg | 3.80 kg | 3.68 kg |
| 5.0 kg | 5.25 kg | 4.75 kg | 4.60 kg |
| 6.0 kg | 6.30 kg | 5.70 kg | 5.52 kg |
Winter reserve or the start of obesity
Appetite rises as daylight falls below 11 hours and the cat sleeps more, so a 3 to 5 percent gain between October and December is expected physiology, not a failure. On a 4 kg cat that is 120 to 200 grams. The line is 8 percent: above that, the gain is fat, not reserve, and a cat that enters spring 8 percent heavier carries most of it into summer. Check body condition with hands, not eyes: ribs felt under a thin fat layer with light pressure scores 5 of 9, ribs you must press for scores 6 or 7, and no ribs at all scores 8.
Autumn room numbers that change intake
Indoor temperature drives intake more than most owners expect. Keep the room at 18 to 22 degrees C; below 16 the cat eats more to hold heat, above 24 it moves less. Relative humidity of 40 to 60 percent keeps the coat and airway comfortable, and above 70 percent cats tend to lie still on cool floors. A cat on free feeding typically takes in 10 to 15 percent more food in the 8 weeks after the clocks change, which on a 250 kcal day is 25 to 38 extra kcal, roughly 30 grams of dry food. That surplus is fine for a lean cat and too much for a cat already at 6 of 9 body condition. Measure the daily ration with a kitchen scale for 7 days in October; most owners overestimate a scoop by 15 to 20 percent, and a 10 gram daily error becomes 300 grams over a month.
Weight down in autumn needs a reason
Autumn loss is not seasonal, so treat it as a symptom. A 5 percent drop with a good appetite points at hyperthyroidism or diabetes; with a poor appetite, at dental pain, nausea, or kidney disease (CKD). Cats over 10 years old lose muscle before they lose fat, so a senior can look the same size and be 300 grams lighter. Ask for a full panel with T4, renal values, and urine, and weigh again in 30 days to see whether treatment moved the line. Dental checks belong in the same visit; the autumn indoor mold piece covers the respiratory side of a closed-up house, and the toxicity lookup screens any new plant or product before it enters the room.
One weigh-in, four controls
- Same scale, same floor spot, checked with a 2 kg weight each season.
- Between 06:00 and 08:00, after the litter box, before the first meal.
- Two readings 30 seconds apart, recorded to the nearest 5 grams.
- Compare with the September baseline and mark the 5 and 8 percent lines on the sheet.
- Reweigh in 14 days after any change over 5 percent, and book a vet if it holds.
Terms mentioned in this article
Frequently asked
My cat gained 400 grams since September. Is that normal?
On a 4 kg cat that is 10 percent, which is past the 8 percent line where gain is fat rather than winter reserve. Normal seasonal gain for that cat is 120 to 200 grams. Cut the daily ration by 10 percent, stop free feeding, and reweigh in 30 days; if the number has not moved, ask for a body condition score and a calorie target.
Why is my cat losing weight in autumn?
Weight loss is not seasonal, so treat it as a symptom. A 5 percent drop with a good appetite points toward hyperthyroidism or diabetes, and with a poor appetite toward dental pain, nausea, or kidney disease. Cats over 10 years lose muscle before fat, so ask for a panel with T4, renal values, and a urine test, then reweigh in 30 days.
Can I weigh the cat on a human bathroom scale?
You can, but the error is 200 to 400 grams, which is the whole 5 percent line on a 4 kg cat. Weigh yourself, then yourself holding the cat, and subtract, three times in a row, and only trust the result if all 3 numbers agree within 100 grams. A 5 gram pet or kitchen scale with a towel is far more reliable.