The instinct with an overweight pet is to cut the food hard and get it over with. That is the one approach that reliably backfires: lose weight too fast and what comes off is muscle, not fat — and in cats, rapid loss can trigger a life-threatening liver condition.
Slow is not a compromise here. It is the method.
How we label our evidence
- Source-supportedStated directly in the cited institutional publication.
- Our editorial guidanceA conservative reading of the evidence applied to a caregiver decision. Not a validated clinical protocol.
- Evidence gapWe could not verify this in our approved sources, so we have not invented a number.
Safe rates
| Species | Per week | A 30 kg dog / 6 kg cat |
|---|---|---|
| Dogs | 1–2% of body weight | 300–600 g per week |
| Cats | 0.5–1% of body weight | 30–60 g per week |
Those numbers look slow because they are. A dog that needs to lose 5 kg is on a three-to-four month project, not a three-week one. The calculator's weight log exists to make that timescale tolerable — you can see the trend even when a single week looks like nothing happened.
How the calorie target is set
When you switch the goal to weight loss, the calculation changes shape. Instead of resting energy × an activity factor, it becomes:
- Dogs: RER × 1.0
- Cats: RER × 0.8
Critically, that RER is calculated from the ideal weight, not the current one — which is why getting the body condition score right matters more in weight-loss mode than anywhere else on the site.
Cats
This is the important one. Cats that lose weight too rapidly — particularly overweight cats that stop eating — can develop hepatic lipidosis, or fatty liver disease. Fat mobilised faster than the liver can process it accumulates there, and the condition can be fatal.
Do not exceed 1% a week. If an overweight cat stops eating for any reason, that is not a convenient head start on the diet — it is a reason to call the vet.
Measuring, not guessing
- Re-weigh every two weeks and adjust by 5–10%. Individual variation from any calculated figure reaches ±50%, so the number you start with is a hypothesis you then test.
- Weigh the food. Measuring cups are off by 30% or more depending on kibble density. A deficit you intended can vanish entirely into cup error.
- Count the treats. They come out of the daily total — see the 10% rule.
When to involve a veterinarian
What the action labels mean
- Emergency now —
- contact an emergency veterinary service and arrange immediate assessment. Do not wait for the next scheduled feed or weigh-in.
- Call now for triage —
- telephone the veterinary service when you notice the sign. The veterinarian decides how quickly the animal needs to be seen.
- Contact today —
- get in touch when you notice the issue to agree on a time. This does not mean waiting until evening.
Call now for triage
Contact today
Contact today
Sources
- AAHA 2021 Nutrition and Weight Management Guidelines for Dogs and Cats
- Today's Veterinary Nurse (2022) Energy Calculations
- Pet Nutrition Alliance Calculating Calories Based on Pet Needs