Updated
Cat ideal weight calculator
Score your cat’s body condition on the 9-point WSAVA scale, and this page turns it into an ideal weight by the rule veterinarians use — each point above or below 5 is about 10 % of body weight — then into a safe timeline at the feline rate. Three steps most guides leave you to do alone.
9.9 lb, ideal weight
+30 % from ideal: lose 3.1 lb over 23.1–46.2 weeks at 0.5–1 % of body weight a week.
- Rule: each BCS point away from 5 ≈ 10 % of body weight (Laflamme 1997)
- 13 lb ÷ (1 + 0.1 × 3) = 9.9 lb
- Range (10–15 % per point)
- 9 lb to 9.9 lb
- Weeks to goal at 0.5–1 % a week (faster risks hepatic lipidosis)
- 23.1 weeks at the fast rate, 46.2 at the slow rate
- Next step
- Feed to the ideal weight, not today’s: the cat food calculator’s weight-loss mode takes the ideal weight and the WSAVA factor.
- See a vet
- A score of 8 is outside what a home plan should handle alone (3 and below, 8 and above).
What this means
Body condition score is a hands-on measure, and it is what the ideal weight comes from — not the breed average, which says nothing about this animal’s frame. Feel for the ribs, look for a waist from above and a tuck from the side, and pick the score that matches the chart.
The 10 %-per-point rule is Laflamme’s approximation: her work found each point to be 10–15 % of body weight, which is why the range row exists. Safe loss for cats is 0.5–1 % a week — faster risks hepatic lipidosis, a liver disease that can be fatal; several online tools quote the wrong unit or the wrong species.
Weight loss is planned on the ideal weight, not the current one: the diet’s calories come from the target weight’s resting energy, which is what the feeding calculator’s weight-loss mode does.
When to see a vet
- A score of 8 or 9: obesity at this level needs a supervised plan and a check for underlying disease.
- A score of 3 or below, or any cat losing weight without a diet change — thinness is a symptom before it is a feeding question.
- Weight changing faster than 0.5–1 % a week on any plan.
- A cat that stops eating during a diet: cats must never be starved to lose weight.
Formula and sources
Sources reviewed 18 September 2026. Each names the figure it supports.
- The 9-point body condition score and the 10–15 % of body weight per point behind the ideal-weight rule — Laflamme D. P., "Development and validation of a body condition score system for dogs", Canine Practice 22(4), 1997; and "… for cats: a clinical tool", Feline Practice 25(5–6), 1997
- The body condition score descriptors beside the selector (dog) — WSAVA Body Condition Score chart, dogs
- The body condition score descriptors beside the selector (cat) — WSAVA Body Condition Score chart, cats
- Safe weekly loss (dogs 1–2 %, cats 0.5–1 %) and planning the diet on the ideal weight — AAHA Nutrition and Weight Management Guidelines for Dogs and Cats, 2021
This page is an educational estimate, not veterinary advice.
Frequently asked questions
What should my cat weigh?
Score the body condition on the 9-point scale, then divide today’s weight by 1 plus 0.1 for every point above 5 (or 1 minus 0.1 for every point below). A 13 lb cat at score 8 has an ideal weight of about 9.9 lb.
How do I body-condition score my cat?
Run your hands along the ribs: at an ideal 5 they are easy to feel under a thin layer of fat, like the back of your hand. From above there is a visible waist behind the ribs; from the side the belly tucks up. If you have to press to find ribs, the score is 6 or more; if you can see them, 4 or less. The WSAVA chart in the sources shows every score.
How fast can a cat lose weight safely?
About 0.5–1 % of body weight a week. Faster than that risks hepatic lipidosis, a liver disease brought on when a cat’s body mobilises fat too quickly, which is why cat diets are slower than dog diets and why a cat must keep eating throughout.
How much should I feed a cat to lose weight?
Calories for the ideal weight, not the current one: the resting energy of the target weight times the WSAVA weight-loss factor (0.8). The cat food calculator’s weight-loss mode does that sum when you enter the ideal weight from this page.