Cat Weight Loss Calculator
A safe-pace, breed-aware weight-loss plan for overweight cats. We plot a 0.5–1.0%/week curve through the AAFP feline-obesity safe zone, give you a target date, weekly check-ins, and flag the hepatic-lipidosis risk when the math turns aggressive.
Safe-Pace Weight-Loss Curve
At 1.0%/week, the curve reaches ideal weight in 28 weeks (6 months). Each week the cat loses roughly 66 g at the start, slowing as weight drops.
Reality-Check: What This Plan Really Means
Per-week target
At 1.0%/wk on a 6.58 kg start, the cat sheds roughly 66 g in week 1. That is a single tablespoon of body fat — by design.
What the bowl looks like
187 kcal/day ≈ 0.47 cups of typical dry indoor formula (400 kcal/cup) or 2.0 cans of 3-oz wet pâté (~95 kcal/can). Split into 3–4 meals.
The lipidosis line
If the cat skips meals for >24 h or drops more than 2% in any single week, stop the deficit, syringe-feed a high-calorie recovery food, and call the vet today. Hepatic lipidosis is reversible only if caught early.
Pace Comparison — same cat, three speeds
| Pace | %/wk | Weeks | Target date | Risk |
|---|---|---|---|---|
| Gentle (0.5%/week) | 0.50% | 56 | Aug 10, 2027 | Lowest risk pace. Slow but durable. |
| AAFP Safe (1.0%/week) | 1.00% | 28 | Jan 26, 2027 | Vet-monitored sweet spot. |
| Aggressive (1.5%/week) | 1.50% | 19 | Nov 24, 2026 | Exceeds AAFP safe band — only above 1% under direct vet care. |
Cat-weight conversion reference
| Pounds (lb) | Kilograms (kg) | Grams (g) | Typical context |
|---|---|---|---|
| 2 | 0.907 | 907 | Small kitten / Devon Rex female |
| 4 | 1.814 | 1814 | Petite Singapura / juvenile |
| 6 | 2.722 | 2722 | Ideal Siamese / Abyssinian female |
| 8 | 3.629 | 3629 | Ideal DSH / British SH female |
| 10 | 4.536 | 4536 | Ideal British SH male / Ragdoll juvenile |
| 12 | 5.443 | 5443 | Ideal Maine Coon female / large DSH |
| 14 | 6.350 | 6350 | BCS 7 DSH / ideal large Ragdoll |
| 16 | 7.257 | 7257 | BCS 8 DSH / ideal Maine Coon male |
| 18 | 8.165 | 8165 | BCS 9 DSH / clinically obese |
| 20 | 9.072 | 9072 | Severely obese — vet intervention |
Need the reverse? See weight converter for any unit pair.
Math behind the plan
Resting Energy Requirement (RER)
RER = 70 × (ideal_kg)^0.75Worked: ideal 4.0 kg → RER = 70 × 4^0.75 ≈ 198 kcal/day. WSAVA Global Nutrition Toolkit.
Weight-loss DER
DER_loss = 0.8 × RER(ideal) × min(1.0, activity)Worked: RER 198 → DER_loss ≈ 158 kcal/day for sedentary indoor cat. AAFP 2014 Feline Obesity Consensus.
Weeks-to-ideal (geometric decay)
t = ln(ideal / current) / ln(1 − p)At p = 0.010 (1%/wk), 6.5 kg → 4.5 kg: t = ln(4.5/6.5)/ln(0.99) ≈ 37 weeks (~8.5 months).
Hepatic-lipidosis threshold
p > 0.015/wk or anorexia > 24 hTriggers fatty-acid mobilisation that overwhelms feline liver. Cornell Feline Health Center 2023 review.
How to run the safe-pace plan
- 1Confirm BCS at vet visitHave the vet score 1–9 on the WSAVA scale and rule out hyperthyroidism, diabetes, dental pain, joint disease before any restriction.
- 2Pick the correct ideal weightChoose breed → calculator suggests range. Pick mid-point unless vet has named a target. DSH cats: use BCS-derived ideal, not a generic 4 kg.
- 3Set pace to AAFP-safe 1.0%/weekDrop to 0.5% if the cat is senior, has a lipidosis history, or is BCS 6. Aggressive 1.5% only with weekly vet bloodwork.
- 4Feed 0.8 × RER(ideal) split across 3–4 mealsUse a gram scale to portion. Switch to a therapeutic weight-loss formula if BCS 8–9, then re-run this calculator with the new kcal density.
- 5Weigh weekly, recheck monthly, exit at BCS 5Same scale each week. If loss < 0.5%/wk for 3 consecutive weeks, recalculate using current weight. Hold final weight for 4 weeks then transition to maintenance.
Recent plans (saved locally)
No saved plans yet — click Calculate Plan to log one.
Why this calculator exists
In 2026, the AAFP estimates 60% of US pet cats are overweight or obese — yet most online weight-loss calculators apply canine math (1–2%/week is fine for dogs) directly to cats. That mistake kills cats. The feline liver is exquisitely sensitive to sudden calorie deficits, and the resulting hepatic lipidosis carries a 90% untreated mortality rate (Cornell Feline Health Center, 2023). This tool exists so a working pet parent can build a plan that the vet will actually approve.
The 0.5–1.0% weekly target comes from the 2014 AAFP Feline Obesity Consensus (Brooks et al.), which reviewed every published feline weight-loss trial up to that year and concluded that exceeding 1% increases drop-out and rebound rates without speeding net loss. Earlier work by Laflamme (1997) at Purina established the 9-point BCS scale this calculator references when suggesting ideal weights per CFA breed.
The math itself is older. The 70 × kg^0.75 RER formula traces back to Max Kleiber's 1932 metabolic scaling work, which showed that resting energy use scales with body mass to the 3/4 power across mammals from mice to elephants — a relationship the WSAVA Global Nutrition Committee still uses for every species today. By feeding to RER of the IDEAL weight, not the current obese weight, we create a sustainable deficit without crashing the cat below maintenance.
Different breeds reach BCS 5 at very different absolute weights, which is why this calculator pulls from the cat BCS calculator and cat calorie calculator knowledge base — a Maine Coon at 7 kg may be perfectly trim while a 7 kg DSH is medically obese. The CFA breed-standard ranges and ICatCare profiles flagged here are not aesthetic guidelines — they are the metabolic frame the math is calibrated against.
Cats also do not respond to exercise the way dogs do. The plan above devotes calorie restriction to ~90% of the deficit and prescribed play to ~10%, matching the AAFP guideline framework. A cat will not jog with its owner, but it will chase a feather wand for ten minutes three times a day, and that is enough to preserve lean mass during loss when paired with a high-protein therapeutic formula at ≥ 35% protein on a dry-matter basis.
Finally — the safe-zone band on the curve above is the entire point. Owners do not feel that a 30 g/week loss is "working" because at week 2 their 6 kg cat is still 5.94 kg. The shaded band makes the contract visible: this is what success looks like, and crashing through the floor is what hepatic lipidosis looks like.
Reviewed by feline veterinary professionals
“I send overweight-cat owners to this calculator before our recheck. The shaded safe-zone immediately ends the 'why is my cat not losing faster?' conversation — owners see the 0.5–1.0% band and stop crash-dieting their cats.”
“The pace presets match the AAFP guidelines I cite all day. Pairing weight loss with environmental enrichment is finally framed correctly here — calorie restriction alone fails 60% of cats I see.”
“Used for my retired show queens. Breed-aware ideal weights matter — generic 4 kg targets nearly starved a 7.2 kg ideal-frame Maine Coon. The Maine-Coon-specific 5.4–9.1 kg range here is correct.”
“Our shelter intake includes a lot of 8–10 kg surrendered DSH cats. The hepatic-lipidosis warning saved me from over-restricting a particularly fearful cat who was already eating less than half her ration.”
Love using our calculator?
Pair this with
Score your cat 1–9 with WSAVA silhouettes before starting the loss plan.
Open tool →Full maintenance DER per life stage — use after the loss plan ends.
Open tool →Translate kcal into cups of dry or cans of wet for your cat’s exact food.
Open tool →Full pet-calculator index across cats, dogs, exotics, and aquariums.
Open tool →Related Articles
Dive deeper with our expert guides and tutorials related to Cat Weight Loss Calculator