Putting a cat on a diet is not the same as putting a dog on one. Cats are more at risk if they eat too little or lose weight too fast, and many will refuse a food they dislike. That makes planning and checking more important, not less. This guide explains how a weight-loss plan is put together: the starting calories, how they turn into grams, what a safe pace looks like on the scale, how treats fit and what should make you call the vet. It gives the numbers our calculator uses so you can follow them, but the plan itself is for your vet. If you have not yet worked out how far over your cat is, start with how overweight is my cat.
The starting point
Daily energy for weight loss in our cat calculator is:
kcal a day = 0.8 × 70 × (ideal weight in kg)^0.75
The ideal weight is the one your vet gives. Using it instead of today’s weight sets the cat up to finish at the right place. The 0.8 factor sits below the 1.2 used for a neutered adult at maintenance and the 1.0 used for an inactive adult. See cat RER and MER explained.
| Ideal weight | RER | Weight-loss start (0.8 × RER) | Maintenance (1.2 × RER) |
|---|---|---|---|
| 3.5 kg | 179 | 143 | 215 |
| 4.0 kg | 198 | 158 | 238 |
| 4.5 kg | 216 | 173 | 260 |
| 5.0 kg | 234 | 187 | 281 |
| 5.5 kg | 251 | 201 | 302 |
These are starting points to discuss with the vet. The vet can raise or lower the number after the first weigh-ins.
From calories to grams
Grams a day = kcal ÷ kcal per gram of the food.
| Ideal weight | kcal a day | Dry food at 3.8 kcal/g | Wet food at 0.9 kcal/g |
|---|---|---|---|
| 3.5 kg | 143 | 38 g | 159 g |
| 4.0 kg | 158 | 42 g | 176 g |
| 4.5 kg | 173 | 46 g | 192 g |
| 5.0 kg | 187 | 49 g | 208 g |
| 5.5 kg | 201 | 53 g | 223 g |
A cat on a reduced diet needs a precise scale: a 42 g portion is small, and a 5 g error is 12% of the day. See how to split a day’s food into meals for dividing the total without drifting.
Why not just feed less of the usual food
A smaller portion cuts calories but also cuts everything else in the food: protein, vitamins, minerals. A food is balanced for a cat eating the amount it is made for. At about 58% of what a 5.4 kg cat would need at maintenance, a cat on an ordinary food may fall short of some nutrients. That is why vets often recommend a diet formulated for weight loss, which has more nutrients per calorie. Whether that applies to your cat is a decision for your vet. Do not switch foods suddenly; see how to switch dog food for the general idea of a gradual change, and ask your vet for cat-specific advice.
The pace
The AAHA guidelines describe about 1 to 2% of body weight a week as a safe general range. For cats your vet decides, and many cats are kept at the lower end.
| Cat | Weekly loss at 1% | Weekly loss at 2% |
|---|---|---|
| 5.4 kg | 54 g | 108 g |
| 5.0 kg | 50 g | 100 g |
| 4.5 kg | 45 g | 90 g |
These amounts are small. A cat that loses 54 g a week has lost 216 g in a month, about the weight of a large apple, and the scale has to read to 10 to 50 g to see it. If a cat loses faster than the plan, do not celebrate; call the vet. Loss that is too fast is a risk to the cat.
When to call the vet
- The cat eats much less than the plan or stops eating.
- The cat loses weight faster than the agreed pace.
- The cat seems unwell, tired or hides.
- The weight does not move for several weeks.
- You are unsure whether the food or amounts are right.
Phone first, and say what the cat has eaten and for how long. This list is general; your vet may give you more specific warning signs.
Treats, toppers and multi-cat homes
Treats count. Keep them inside the plan, at a small share of the day; see treat calories per treat for the sums. In a home with more than one cat, a diet for one cat is hard to run if the others eat from the same bowl. Feed in separate rooms, at set meal times, or use a feeder that recognises each cat. Remember that other cats may need a different amount; see indoor cat calorie needs.
Making it last
Weight regained after a diet is a common outcome, so the end of the plan needs a plan too. At the goal weight the calories rise to maintenance for the new weight, and the weigh-ins continue. Our Pet Weight Goal Date Calculator gives a date for the end of the loss phase, and the vet will set the maintenance amount.
A worked example
Rina’s cat weighs 5.4 kg and the vet has set an ideal weight of 4.5 kg with a slow plan.
| Step | Working | Result |
|---|---|---|
| Weight-loss start | 0.8 × 70 × 4.5^0.75 | 173 kcal a day |
| Dry food | 173 ÷ 3.8 | 45.5 g (46 g) |
| Treats | 5% of the day | 9 kcal, about 2 small treats |
| Meal food after treats | 173 − 9 | 164 kcal, 43 g |
| Weekly loss at 1% | 5.4 × 0.01 | 54 g |
| Check at 4 weeks | about 5.2 kg |
Rina feeds 43 g of the food in two meals, weighed on a scale that reads to 1 g, and gives two small treats a day. She weighs her cat every two weeks, sends the weights to the clinic and rings if her cat misses a meal. At the first review the vet keeps the plan the same.
A check-in routine
A plan works when the numbers are looked at on a schedule. A simple routine for the first three months:
| When | What to do |
|---|---|
| Day 1 | Weigh, photograph the cat from above and the side, write down the daily grams |
| Every 2 weeks | Weigh on the same scale at the same time, record the weight and the change |
| Every 4 weeks | Send the numbers to the vet’s nurse or book a weigh-in |
| Any time | Call the vet if the cat eats little, hides or seems unwell |
At each check, compare the weight with the plan.
| Result against the plan | What it suggests | What to do |
|---|---|---|
| On track | The amount is about right | Keep going, keep the log |
| Faster than planned | The pace may be too quick | Tell the vet before changing anything |
| Slower than planned | Extras or too-large portions | Re-weigh the food and count treats, then ask the vet |
| No change for several weeks | The plan may need review | Ask the vet; do not cut food on your own |
Keep the photographs: a change in shape can be clearer than a change in weight over a few weeks. Over a three-month plan the log gives your vet a record to adjust from, which is better than memory.
Questions for the vet at the first visit
Going in with questions makes the first visit more useful.
- What is my cat’s ideal weight, and how did you decide it?
- Is there any medical reason for the weight gain that we should check first?
- What daily calories do you advise, and is my cat’s current food right for a weight-loss plan?
- What pace of loss do you want, and what should I do if my cat loses faster or slower?
- How often should I weigh, and do you want the numbers sent in?
- How many treats are allowed, and which ones?
- What signs should make me phone you straight away?
- When do we review the plan, and what happens at the goal weight?
Write the answers on the same page as the calorie figures, so that everyone in the house follows one plan. If your cat shares a home with others, ask how to feed them separately.
Common mistakes
- Feeding for the current weight, not the ideal.
- Cutting a regular food without asking the vet.
- Using a scale too coarse to see a trend.
- Ignoring treats.
- Letting the cat go without food.
- Not weighing for weeks.
- Forgetting a plan for maintenance.
Quick summary
- Starting energy = 0.8 × 70 × (ideal weight)^0.75; 158 kcal for a 4 kg ideal.
- That is about 42 g of dry food at 3.8 kcal/g or 176 g of wet at 0.9.
- The pace is slow, and your vet sets it; fast loss can make a cat seriously ill.
- Weigh every one to two weeks on a fine scale.
- Call the vet if the cat stops eating or loses too fast.
- Use the Cat Calorie Calculator.
Frequently asked questions
How many calories should a cat eat to lose weight?
A starting point is 0.8 × the RER of the ideal weight. For a 4 kg ideal that is 158 kcal a day. Your vet may change it.
Why use the ideal weight and not the current weight?
Feeding for the weight you want the cat to reach means the plan ends at the right place instead of stalling above it.
How fast should a cat lose weight?
Slowly and as your vet advises. AAHA gives a general range of 1 to 2% a week, and cats are often kept at the lower end.
Can I just feed less of the usual food?
Ask your vet. A smaller portion of an ordinary food can leave nutrients short, and some cats need a diet made for weight loss.
What if my cat stops eating?
Phone your vet at once. A cat that eats very little can become seriously ill.
How do I know it is working?
Weigh every one to two weeks on a fine scale, record the numbers and compare with the planned pace.
Sources
- AAHA (2014) Weight Management Guidelines for Dogs and Cats. Journal of the American Animal Hospital Association 50:1-11
- NRC (2006) Nutrient Requirements of Dogs and Cats, National Academies Press: RER = 70 × kg^0.75
- AAFP/AAHA (2021) Feline Life Stage Guidelines. Journal of Feline Medicine and Surgery 23:211-233
Related calculators
- Cat Calorie CalculatorWork out how many calories your cat needs each day, from its weight and life stage.
- Pet Weight Goal Date CalculatorEstimate the date a pet could reach its goal weight at a steady weekly loss, inside the 1–2% a week range.
- Pet Weight Change CalculatorTrack a weight change over time: percent change, percent per week and whether the pace is inside 1–2% a week.
Keep reading
- How Overweight Is My Cat? Percent Over IdealHow far over ideal weight is a cat? (current − ideal) ÷ ideal × 100, the 10% per body-condition-point rule, a 4 kg ideal table and a worked 5.4 kg cat.
- Cat RER and MER ExplainedCat RER and MER explained: how resting energy (70 × kg^0.75) becomes a daily calorie target with life stage factors, worked examples, treats and common mistakes.
- How to Weigh a Cat at HomeHow to weigh a cat at home: baby scale, kitchen scale and box, carrier method or hold-and-subtract, how big the error is for a 3 to 6 kg cat and how to log weights.
- Indoor Cat Calorie NeedsHow many calories an indoor cat needs: RER × 1.0 if inactive versus 1.2 if neutered, a 3 to 6 kg table in kcal and grams, and how to adjust by weight trend.