Diet Plans for Dogs and Cats: Ideal Weight, Daily Calories and How Long It Takes
You may notice your pet getting a little heavy, but it's hard to tell how much to lose or how many months it will take. A dog or cat diet goes smoothly and reliably if you set the calories by working back from a target weight rather than "just cutting a little." This article explains how to estimate ideal weight from BCS (a body condition score), the calorie formula during weight loss, what percentage to lose per week, a chart of how long it takes, and hepatic lipidosis, which needs special care in cats.
First, use BCS to see how overweight your pet is
Weights vary so widely by breed and frame that a number alone can't tell you whether a dog or cat is overweight. That's what BCS (body condition score) is for. It scores body shape by how the ribs feel and how the body looks from above and from the side. On the 9-point scale, 5 is ideal, and higher numbers mean heavier.
| 9-point | 5-point | Body type | How it looks and feels |
|---|---|---|---|
| 4 | 2.5 | Slightly thin | Ribs easily felt. A visible waist from above |
| 5 | 3 | Ideal | Ribs felt under a thin layer of fat. Waist tucks in from above |
| 6 | 3.5 | Slightly heavy | Ribs can be felt but the fat is somewhat thick. Waist isn't obvious |
| 7 | 4 | Heavy | Ribs are hard to feel. Almost no waist |
| 8 | 4.5 | Obese | Ribs only felt with firm pressure. Belly sags |
| 9 | 5 | Severely obese | Ribs can't be felt. Fat on the neck, limbs and back too |
Checking is simple. Stroke the sides of the chest with both palms. If the ribs feel like the bones on the back of your hand, that's ideal; if they feel like the palm side, barely detectable under fat, your pet is on the heavy side. Cats tend to have saggy belly skin, so focus on how the ribs and backbone feel.
Estimating ideal weight from BCS
Each step above 5 on the 9-point BCS is thought to be about 10% over ideal weight. With this guide, you can estimate ideal weight from current weight and BCS.
| Current weight and BCS | Estimated ideal weight | Amount to lose |
|---|---|---|
| Cat 5 kg, BCS 6 | About 4.5 kg | About 0.5 kg (9%) |
| Cat 6 kg, BCS 7 | 5 kg | 1 kg (17%) |
| Dog 6 kg, BCS 6 | About 5.5 kg | About 0.5 kg (9%) |
| Dog 8 kg, BCS 8 | About 6.2 kg | About 1.8 kg (23%) |
| Dog 12 kg, BCS 7 | 10 kg | 2 kg (17%) |
This is only an estimate, so if you know your pet's weight when young, that makes a more accurate target. If a plan means losing 25% or more of current weight, don't aim straight for the final goal; make an intermediate weight the first target and go in stages.
Calculate daily calories during weight loss from the target weight
A common mistake is cutting a little from the amount calculated for the current weight. That amount maintains the overweight body, so the weight doesn't fall as hoped. During weight loss, multiply the RER at the target weight by the weight-loss factor (1.0 for dogs and 0.8 for cats).
| Example | To maintain current weight | Calories during weight loss | Food (360 kcal/100 g) | Diet food (300 kcal/100 g) |
|---|---|---|---|---|
| Cat 6 kg → target 5 kg | About 322 kcal | About 187 kcal (RER 234 at 5 kg × 0.8) | About 52 g | About 62 g |
| Cat 5 kg → target 4.5 kg | About 281 kcal | About 174 kcal | About 48 g | About 58 g |
| Dog 6 kg → target 5.5 kg | About 429 kcal | About 250 kcal | About 69 g | About 83 g |
| Dog 12 kg → target 10 kg | About 722 kcal | About 394 kcal (RER at 10 kg × 1.0) | About 109 g | About 131 g |
"To maintain current weight" in the table uses the spayed or neutered factors (1.6 for dogs and 1.2 for cats). Calories during weight loss look much lower, but that's the amount at which weight falls gradually. Low-calorie diet food gives about 20% more grams for the same calories, easing the feeling of eating less.
What percentage to lose per week, and how long it takes
The pace to aim for is 1–2% of body weight a week for dogs and 0.5–2% for cats. Any faster and muscle may be lost and rebound becomes more likely. These are the weeks to reach the target, calculated as losing a given percentage of the current weight each week.
| Plan | 0.5%/week | 1%/week | 1.5%/week | 2%/week |
|---|---|---|---|---|
| Cat 6 kg → 5 kg | 37 weeks | 19 weeks | — | 10 weeks |
| Cat 5 kg → 4.5 kg | — | 10 weeks | — | — |
| Dog 6 kg → 5.5 kg | — | 10 weeks | — | — |
| Dog 12 kg → 10 kg | — | 19 weeks | 13 weeks | 10 weeks |
| Dog 8 kg → 6.2 kg | — | 27 weeks | — | — |
- Even a 1 kg diet takes roughly 4–5 months at 1%/week. It's longer than feels natural to people, so plan in units of several months.
- Weekly loss at 1% is about 60 g for a 6 kg cat and about 120 g for a 12 kg dog. That gets lost in the error of a household scale, so weigh every 2 weeks under the same conditions (in the morning, before eating and so on).
- If the weight hasn't fallen after 2–4 weeks, cut the daily amount by another 5–10%. If it's falling faster than 2%/week, add a little back.
Don't cut suddenly for cats (beware of hepatic lipidosis)
The biggest concern in a cat diet is hepatic lipidosis (fatty liver). When an overweight cat suddenly stops eating or has its food cut sharply, body fat moves rapidly to the liver, liver function falls, and it can be life-threatening.
- Never fast a cat or cut abruptly, such as halving its food
- Don't let the pace exceed 2% a week
- If a cat stops eating after a change of food, don't push on; go back to the old food and consult a veterinarian
- If it barely eats for a day or more, see a veterinarian right away
For dogs too, with a major loss of 25% or more of body weight, or with existing conditions, it's safest to set the target and plan with a veterinarian. Weight gain can also be caused by illness, such as a thyroid condition.
Make a diet plan with the tool
- 1
Enter weight and BCS
In the Dog & Cat Food Portion Calculator, choose the current weight and BCS to get an estimated ideal weight.
- 2
Choose a target and pace in the "Diet plan" tab
You can keep the estimated target weight or enter your own. The pace is 1, 1.5 or 2%/week for dogs and 0.5, 1 or 2%/week for cats.
- 3
Check the daily amount and duration
You'll see daily calories and grams of food during weight loss, the weeks to the target and a graph of weight loss. A warning appears for losses of 25% or more and for rapid loss in cats.
Everyday daily amounts are explained in How Many Grams of Dog Food a Day? and How Many Grams of Cat Food a Day?.
FAQ
- How many kcal a day for an overweight cat on a diet?
- RER at the target weight × 0.8 is the guide. For a 6 kg cat at BCS 7, the ideal weight is about 5 kg and the RER about 234 kcal, so about 187 kcal a day. With food at 360 kcal/100 g, that's about 52 g.
- How many kcal a day for a dog on a diet?
- RER at the target weight × 1.0 is the guide. For a 12 kg dog at BCS 7, the ideal weight is about 10 kg, so about 394 kcal a day. That's about 109 g of food at 360 kcal/100 g, or about 131 g of diet food at 300 kcal/100 g.
- How do I calculate ideal weight from BCS?
- On the 9-point BCS, each step above 5 is about 10% heavier. Ideal weight = current weight ÷ (1 + (BCS − 5) × 0.1), so a 6 kg pet at BCS 7 gives 6 ÷ 1.2 = 5 kg.
- How many months does a diet take?
- Losing 1% of body weight a week takes about 19 weeks (4–5 months) to bring a 6 kg cat to 5 kg, and also about 19 weeks to bring a 12 kg dog to 10 kg. At 2%/week it's about 10 weeks, but don't exceed 2% for cats.
- What should I watch for in a cat diet?
- Suddenly cutting food or fasting risks hepatic lipidosis (fatty liver). Lose 0.5–2% of body weight a week, and if your cat barely eats for days, see a veterinarian right away.
Tools in this article
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