Weight loss for dogs: how fast and how many calories

Plan the calories on the ideal weight

The single most important rule: work out weight-loss calories from the ideal weight, not today’s weight. The 2021 AAHA guidelines give a weight-loss factor of 1.0 × resting energy requirement (RER) for dogs and tell vets to base the calculation on ideal weight. RER is 70 × body weight in kg^0.75.

Worked example. A dog weighs 40 kg (88 lb) and scores 7 on the 9-point body condition scale. Each point above 5 is roughly 10% over ideal weight (AAHA), so:

1. Ideal weight estimate: 40 ÷ 1.2 = 33.3 kg (73 lb). In a study of obese pet dogs, the weight actually lost per point ranged from 5% to 15%, so the estimate’s range is 30.8–36.4 kg (68–80 lb).
2. Resting energy at the ideal weight: 70 × 33.3^0.75 = 971 kcal a day.
3. Weight-loss calories: 1.0 × 971 = 971 kcal a day, treats included.

Calculators that skip step 1 give more food. Applying the same 1.0 factor to today’s 40 kg gives 1,113 kcal (15% more), and using an ordinary maintenance factor on today’s weight gives about 1,670 kcal (72% more) — enough to keep the extra weight on.

The 2014 AAHA weight guidelines offer a stricter starting point, 80% of the ideal-weight RER — 777 kcal a day for this dog. The two AAHA documents differ, and our calculator uses the 2021 factor of 1.0; your vet may choose either, or a therapeutic diet with its own feeding plan.

How the body condition score and the ideal-weight estimate work, including why we divide rather than subtract, is in the body condition score guide.

How fast: 1–2% of body weight a week

The 2014 AAHA guidelines set the target rate of loss for dogs at 1–2% of body weight a week. Merck suggests about 1% a week as a reasonable goal, and the UC Davis veterinary hospital puts the ceiling plainly: “It is generally recommended that pets lose no more than 2% of their body weight per week.”

For the 40-kg dog, 1–2% a week is 0.40–0.80 kg (0.88–1.76 lb) a week at the start. Each week’s loss is a percentage of the dog’s weight that week, so the pounds come off a little more slowly as the dog gets lighter. At those rates, reaching about 33.3 kg takes roughly 9 weeks at 2% a week and 18 weeks at 1% a week.

Faster isn’t better: 2% a week is the upper end in both the AAHA and UC Davis guidance. For puppies and young dogs that are still growing, AAHA says the rate of loss has to be modified. Our planner doesn’t model weight loss for dogs under 1 year; that plan belongs with your vet.

The floor: no lower than 60% of resting energy

There is a limit to cutting. The 2014 AAHA guidelines report that, in the authors’ experience, most pets tolerate restriction down to 60% of the RER for their ideal weight without problems, and that going below 60% raises the risk of nutrient deficiencies. For the example dog, 60% is 583 kcal a day.

If a dog isn’t losing weight even near that floor, the answer isn’t to cut further on your own. Your vet may look for a medical cause, change the diet, or refer you to a veterinary nutritionist.

Treats count inside the budget

A weight-loss plan is a daily calorie budget, and treats, chews and table scraps are part of it. UC Davis advises keeping treats to no more than 10% of daily calories, and AAHA’s 2014 guidelines warn that nutrient imbalances become likely once treats and human food go past 10%.

For the example dog: 10% of 971 is 97 kcal for treats, leaving 874 kcal for the main food. With a dry food labeled 380 kcal per cup and 3,600 kcal per kg, that is 2.30 cups (about 2¼ cups) or 243 g a day. AAHA’s 2014 guidelines suggest weighing dry food on a scale where possible, because a cup can be imprecise — and that matters more when every portion is smaller than usual.

Weigh every 2 weeks and adjust by 10%

The calorie number is a starting point. Merck advises monitoring the dog’s weight every 2 weeks and changing the program if needed; AAHA’s 2014 guidelines suggest checking in every 2 weeks until the right rate is established, then monthly until the ideal weight is reached. AAHA’s adjustment rules, written for weight loss:

• Losing faster than 2% a week: increase calories by 10% — for the example dog, from 971 to 1,068 kcal.
• Losing more slowly than planned, and the plan is really being followed: reduce calories by 10–20% — to about 874–777 kcal — staying above the floor.
• Still losing at the target weight: increase calories by 10% for maintenance.

These 10% steps belong to weight-loss plans; for a dog already at a healthy weight, no guideline sets a fixed step. AAHA also advises re-estimating the ideal weight as the dog slims and its body condition score improves, because the first estimate can be off in either direction.

Your plan, step by step

1. See your vet first to rule out medical causes and agree on a target weight and body condition score.
2. Score body condition and record today’s weight on the same scale you will keep using.
3. Estimate the ideal weight from the score, or use your vet’s target.
4. Set calories at 1.0 × RER of the ideal weight (or the plan your vet prefers), never below 60% of that RER without your vet.
5. Convert to food from the label’s calorie statement, in grams if you can, with treats inside the 10% budget.
6. Weigh every 2 weeks and compare with the 1–2% a week target.
7. Adjust by 10% as above, and re-score body condition as the dog slims.
8. At the goal, move to maintenance calories for the new weight with your vet. For a neutered 33.3-kg dog, AAHA’s maintenance range works out to 1,360–1,554 kcal a day as a starting point — then keep weighing.

Next step

Enter your dog’s weight and body condition score in the pet weight-loss calculator. It estimates the ideal weight with its range, sets daily calories at that weight, shows the 60% floor and the weekly loss at 1% and 2%, and hands the calories to the dog food calculator for cups and grams.