Put an adult cat on a 10 gram scale once a week, and make both the weekday and the hour non-negotiable. Write grams in 1 column, and judge the trend with 1 line: a 5 percent change across 30 days. For a 4.5 kg cat that line sits at 225 grams, and crossing it in either direction is the point to look at the bowl, the teeth, or the blood work rather than waiting for the next checkup.
Once a week beats once a day
Across a single day a healthy adult can swing 50 to 150 grams on meals, water and litter box timing, so a daily habit mostly records noise. One fixed weekly slot sits still enough for a real trend of 100 grams a month to appear. Weekly also stays sustainable: 52 rows a year is a page, while 365 rows is a habit that dies in 3 weeks. The exception is a cat on a weight-loss plan or one recovering from illness, where 2 or 3 weigh-ins a week catch a stall before it becomes a 300 gram loss.
Set the scale up so 10 grams means something
A digital baby scale or a kitchen scale with 10 gram steps is enough for a cat up to 6 kg; above that, 20 gram steps are acceptable because 20 grams is 0.3 percent of 6.5 kg. Put a shallow box or a folded towel on the platform, tare to zero, and set the cat in with all 4 feet down. Take 3 readings inside 10 seconds and note the median rather than the first number you saw, since a shifting cat swings 30 to 50 grams. Never weigh in pounds, and never round to the nearest 100 grams; the line you are watching is 225 grams wide.
Establish a baseline before you judge anything
One number is not a baseline. Take 3 weekly readings, average them, and use that figure as week 0. At the same session, score body condition on the 9 point scale, where 5 is ideal: ribs felt under a thin fat layer, a visible waist from above, a small belly tuck from the side. Write the score next to the weight, because a cat can hold 4.5 kg while losing muscle and gaining fat. Owners who track only weight miss the 8-year-old that is 200 grams lighter and much softer in the loin.
The 30-day 5 percent line, in grams
Five percent is chosen because it is above scale noise and below the point where most owners notice. Use the highest weight of the last 30 days as the reference, not week 1 forever, so a slow drift is caught in the month it happens. The table shows the same line at 5 common weights, plus the safe change rate for a cat on a diet.
| Current weight | 5% in 30 days | Weekly equivalent | Action at the line |
|---|---|---|---|
| 3.5 kg | 175 g | 41 g | recheck in 7 days, check the teeth |
| 4.0 kg | 200 g | 47 g | recheck in 7 days, book blood work |
| 4.5 kg | 225 g | 52 g | recheck in 7 days, book a visit |
| 5.5 kg | 275 g | 64 g | recheck in 7 days, weigh the ration |
| 6.5 kg | 325 g | 76 g | recheck in 7 days, weigh the ration |
A cat losing weight on purpose should move at 0.5 to 1 percent of body weight a week, which is 22 to 45 grams for a 4.5 kg cat, so a 5 percent drop in 30 days is inside a deliberate plan and alarming in a cat that is eating normally. That is why the sheet needs a second column: is this cat on a diet, yes or no. Without it, the same 225 grams reads 2 different ways.
The log page, 8 weeks filled in
| Week | Weight (g) | Change vs week 0 (g) | Change vs week 0 (%) | Note |
|---|---|---|---|---|
| 0 | 4520 | 0 | 0.0 | baseline, BCS 6/9 |
| 1 | 4555 | +35 | +0.8 | new bowl, bigger portion |
| 2 | 4590 | +70 | +1.5 | no change |
| 3 | 4620 | +100 | +2.2 | portion cut to 45 g |
| 4 | 4605 | +85 | +1.9 | stable |
| 5 | 4580 | +60 | +1.3 | stable |
| 6 | 4560 | +40 | +0.9 | stable |
| 8 | 4530 | +10 | +0.2 | back to baseline |
Two tables look redundant and are not: the first converts a percentage into a number you can check against a scale, the second is the actual sheet. Five columns are enough. Add a 6th for appetite, and a 7th only if the cat is on medication, since a drug log already has its own page.
Reading a rise: bowl, boredom, or fluid
A 5 percent gain in 30 days usually traces to portions, treats, or a second cat eating from the same bowl. Weigh the daily ration on a kitchen scale in grams and compare it with the bag's kcal per kg; a 4.5 kg neutered adult needs roughly 200 to 240 kcal a day, and free feeding easily adds 30 percent. A rise that comes with a tight belly, rapid breathing, or a cat that stops jumping is not a diet problem, and fluid or a mass needs a visit within days rather than weeks.
Reading a fall: teeth, kidney, thyroid, gut
A 5 percent loss in 30 days in a cat that eats normally is the pattern most worth a vet visit. Common causes are dental pain, chronic kidney disease, hyperthyroidism, diabetes and intestinal disease, and early blood work plus a urine test separates them better than waiting 3 months. A 10 percent loss in 90 days, or any loss with vomiting, hides under the bed, or a coat that stops being groomed, moves the visit to this week. In cats over 10 years, monthly weighing is fair, since 300 grams a year is 6 percent and easy to miss quarterly.
Portion math that keeps the line flat
Resting energy needs scale with weight to the power 0.7, so a 4 kg cat needs about 25 percent fewer calories than a 6 kg cat, not the 33 percent the weight ratio suggests. Multiply the resting figure by 1.2 for a neutered indoor adult and by 0.8 for a weight-loss plan, then divide by the food's kcal per kg to get grams per day. A 250 kcal plan on a 3.8 kcal per gram food is 66 grams a day. Weigh that portion once, mark the scoop, and recheck the math after every 500 grams of change, because the target moves with the cat.
Five habits that keep the page alive
- Fix 1 weekday and 1 hour, before the first meal, and put it in the calendar as a 3-minute task.
- Store the scale where you feed the cat, so the step is not a decision.
- Write grams only, 4 digits, no units mixing.
- Photograph the page on the 1st of each month as a backup.
- Review 30 days at a time, and never react to 1 reading.
The whole routine costs 3 minutes a week and 1 page a year. It turns questions like is she getting fat into a 30-day number, and it gives a vet a trend instead of a snapshot on the day something is actually wrong.
Terms mentioned in this article
Frequently asked
My cat hates the scale. Can I weigh myself holding her?
Yes, if you subtract your own weight and repeat 3 times, but the error is 100 to 200 grams, which is most of the 5 percent line. Better options are a baby scale with a shallow box, or weighing the cat in its carrier on a luggage scale and subtracting the carrier. A 10 gram step on a proper scale is worth the 20 dollars.
Is 5 percent in 30 days too strict for an older cat?
The line is a trigger, not a diagnosis. In a cat over 10, age-related muscle loss can move weight slowly, but 5 percent in a month is faster than aging and deserves blood work plus a urine test. Keep the same 30-day window and add a monthly body condition score, since muscle loss can show there before the scale moves.
How do I weigh a cat that will not sit still?
Weigh in the carrier, on a luggage scale with a strap, and subtract the carrier weight once. Set the carrier down, let the cat walk in, and read after 3 seconds. Two people help: one holds the carrier steady, one reads. Do it before the morning meal, when the cat is hungry and more likely to cooperate for food.