Twelve weeks takes a 6.2 kg cat to 4.99 kg at 1.5 to 2 percent of body weight a week, which is the range most vets will accept without losing muscle. The mechanics are 3 numbers: a target weight set by body condition, a daily calorie figure 20 percent below what the cat eats now, and a reweigh every 7 days that recalculates the food. The table below can be checked with a calculator.
Set the target from body condition, not from the scale
Body condition is scored 1 to 9. At 5 the ribs are easy to feel under a thin fat layer; at 8 they are hard to find and there is no waist behind the ribs; at 9 there is a belly pad and a rounded back. A 6.2 kg cat at 8 out of 9 usually has an ideal weight of 4.8 to 5.2 kg, so 5.0 kg is the planning target. Weigh monthly and score by hand every 2 weeks: a cat can hold 6.2 kg while trading muscle for fat.
The 20 percent cut, and where it lands
Resting energy is 70 times weight in kilograms to the power 0.75. For 6.2 kg that is 275 kcal, and an inactive indoor cat eating at maintenance takes in roughly 275 kcal a day. Cut 20 percent and the plan starts at 220 kcal. Cut 40 percent and the cat is at 165 kcal, below what it needs to hold lean mass, and most cats respond by begging, then by refusing food altogether.
Measure the current intake for 5 days before cutting anything. Weigh the bowl, weigh what is left, divide by 5. The number is usually 15 to 25 percent above what the label suggests, because treats and the second cat never make it into the estimate.
Why 1 to 2 percent a week is the speed limit
Faster loss in cats costs muscle first and brings hepatic lipidosis, the fatty liver that kills obese cats that stop eating. Below 1 percent a week the plan stalls and the owner gives up. Between 1 and 2 percent, a 6.2 kg cat loses 62 to 124 g a week, which is measurable on a kitchen scale but invisible day to day. A home scale is accurate to 20 to 50 g, so judge progress on a 2 week average rather than a single reading.
| Week | Weight (kg) | kcal per day | Grams at 390 kcal/100 g | Total lost (%) |
|---|---|---|---|---|
| 0 | 6.20 | 220 | 56 | 0 |
| 2 | 5.98 | 214 | 55 | 3.6 |
| 4 | 5.77 | 208 | 53 | 7.0 |
| 6 | 5.56 | 203 | 52 | 10.3 |
| 8 | 5.36 | 197 | 51 | 13.5 |
| 10 | 5.17 | 192 | 49 | 16.6 |
| 12 | 4.99 | 187 | 48 | 19.6 |
Recompute at every weigh-in
Every row of that table comes from one line: kcal per day equals 70 times current weight to the power 0.75, times 0.8. At 5.98 kg the answer is 214; at 5.36 kg it is 197. Recalculating weekly means the deficit stays proportional as the cat gets lighter, instead of shrinking to nothing at month 3.
Then convert to grams once: kcal divided by 3.9 gives grams of a 390 kcal per 100 g dry food, or divide by 0.8 for an 80 kcal per 100 g wet food. Write the gram weight on the lid and feed by scale, not by cup. If the 7 day change is under 0.5 percent, check the scale and the treat count before cutting food.
Never fast an overweight cat past 48 hours
Fasting is not a shortcut in cats. An overweight cat that eats nothing for 48 to 72 hours can start mobilizing fat faster than the liver can process it, and hepatic lipidosis follows. This plan never uses a fasting day: the lowest day is 187 kcal, split into 3 to 4 meals. If the cat refuses food for 24 hours, that is a call to the clinic the same day; no overweight cat should go past 48 hours without eating, with or without a weight plan.
Plateaus: the 3 week rule
A flat week is normal. Three flat weeks in a row is data. Check 3 things in order: the gram weight actually fed, the treat and lickable count, and whether a second person or a second cat is adding food. If all 3 are clean, cut 5 percent of calories, never more, and hold for 2 weeks. Do not go below 0.8 times the resting energy of the target weight — 187 kcal for a 5.0 kg cat — without a vet supervising.
Protein, water and muscle
Weight loss that takes muscle looks like success on the scale and failure in the cat. Aim for 6 to 7 g of protein per kg of target weight, so 30 to 35 g a day for a 5.0 kg target, and keep water at 40 to 60 ml per kg. Wet food helps both: at 80 kcal per 100 g a 187 kcal day is 234 g of food, which is 180 ml of water before the cat drinks anything.
Two checks tell you the loss is fat and not muscle: the ribs get easier to feel at the same time as the waist appears, and the cat still jumps onto the same surfaces. A cat that drops 250 g in 2 weeks, stops jumping and sleeps more is losing the wrong tissue, and the answer is more protein and a slower rate, not a bigger deficit.
Week one checklist
- Score body condition by hand and photograph the cat from above and from the side.
- Weigh 5 days of current food and divide by 5 to get the real starting intake.
- Set the start number at 80 percent of that intake and write the gram weight on the lid.
- Weigh the cat on the same scale, same time of day, every 7 days, and log it next to the grams fed.
- Book a vet check at week 6 with bloodwork if the cat is over 8 years old or lost more than 2 percent in any week.
The plan fails in 2 places: an unmeasured bowl at the start, and a stall that nobody recalculated. Both are arithmetic, not discipline. For the cost side of a 12 week plan, the cost tool and the gram-level feeding plan use the same numbers; the winter calorie note matters if the plan runs through a cold month and the cat starts asking for more.
Frequently asked
Is 1 to 2 percent of body weight a week safe for a cat?
For an overweight cat under supervision, yes, with 1 to 1.5 percent as the safer end and 2 percent reserved for cats well above their ideal weight. The risk above that speed is muscle loss and hepatic lipidosis. Weigh weekly, keep protein at 6 to 7 g per kg of target weight, and stop the cut if the cat goes more than 24 hours without eating.
What do I do when the weight stops moving?
Hold the plan for 3 weeks before changing anything, then check the gram weight actually fed, the treats and lickables, and whether someone else is feeding. If all three are clean, cut 5 percent of calories and hold for 2 weeks. Do not drop below 0.8 times the resting energy of the target weight, which is 187 kcal for a 5.0 kg cat, without a vet.
Can I just feed less of the current food instead of switching?
Yes, and it is the simplest start: 80 percent of the measured intake, weighed in grams, with the treats deducted from that total. The catch is nutrient density. Once calories fall below about 187 kcal a day, a maintenance food may not deliver enough protein and the B vitamins, so many vets move the cat to a higher-protein, lower-calorie formula at that point.