Dog weight gain calculator

Before adding food: find out why your dog is thin

A thin dog that eats well is telling you something. Parasites, dental pain and illness can all cause weight loss, and more food will not fix them. AAHA's nutrition guidelines treat a body condition score below 4, any muscle loss, or an unexplained change in weight as reasons for a fuller nutritional assessment. The ASPCA's shelter protocol classes any dog scoring 1, 2 or 3 as malnourished.

Some dogs are simply lean, active or picky. Once your vet has ruled out a medical cause, the plan is straightforward: feed for the weight you want, and check progress every week or two.

How the weight gain calculator works

Target weight. Cornell's Riney Canine Health Center says each point on the 9-point score away from ideal is roughly 10% of the dog's current weight. Ideal is 4 to 5, so a dog scoring 3 aims for about 10 to 20% more weight, and the calculator uses the middle of that range. You can also enter a target your vet has set.

Calories. The goal is the daily energy requirement (DER) of the target weight, using the multipliers in the Merck Veterinary Manual and the ASPCA protocol: 1.6 × RER for a spayed or neutered adult and 1.8 × RER for an intact one.

Daily calories = 70 × (target weight in kg)^0.75 × 1.6 (neutered) or 1.8 (intact)

Worked example: a 40 lb (18 kg) neutered dog scoring 3 aims for 44 to 48 lb, so a target of about 46 lb (20.9 kg). Daily energy at that weight is about 1,090 kcal, against 980 kcal for its current weight. The gap of about 110 kcal a day is what drives the gain.

Refeeding a very thin or starved dog

A dog that has gone without enough food for a long time cannot jump straight to full meals. Refeeding syndrome happens when nutrients flood back in: the ASPCA describes it as low blood potassium, phosphorus and magnesium, and its protocol adds thiamine and vitamin B12 for every dog being refed. The protocol builds up over two weeks, starting from the dog's resting needs at its current weight:

The ASPCA puts an emaciated dog's ideal weight at 20 to 30% above its starting weight and notes it may need raising again after 3 to 6 weeks. Do this with your vet, who can check bloodwork in the first days. Turn on "Starved or not eating recently" in the calculator to see the plan for your dog; it also switches on automatically for scores of 1 and 2.

How fast should an underweight dog gain weight?

Honestly, nobody has published a standard weekly rate for pet dogs, so the calculator asks you for one and shows 1% a week only as an example. What the ASPCA protocol does give is a brake: during the first week the aim is to hold weight steady, and a gain of more than 5% above the starting weight means the dog is being fed too much. After that, weigh every week or two and adjust the food by small steps. Steady progress over weeks is the goal, not a fast number on the scale.

Adding calories the right way

Most of the extra calories should come from a complete and balanced dog food, because it carries the protein, vitamins and minerals a thin dog needs to rebuild. Toppers, oils, chews and weight-gain powders count as extras: AAHA warns that once unbalanced foods make up more than 10% of daily calories, they start to dilute the nutrients in the main diet. If your dog struggles to eat enough volume, ask your vet about a more energy-dense complete food. Our posts on homemade weight gainers and weight gain powders cover the options, and the dog calorie calculator handles maintenance once your dog reaches its target.