How Many Calories Your Pet Actually Needs
Every feeding guideline on every bag of pet food is a starting point for an average animal. The arithmetic that produces a number for your animal is straightforward, and it starts with one formula.
Resting energy first
Resting Energy Requirement is what an animal burns doing nothing, and it scales with body weight to the power of three-quarters rather than linearly:
RER = 70 × (weight in kg)0.75
That exponent is why a 40 kg dog does not need four times what a 10 kg dog needs. The calorie calculator gives 394 kcal for the 10 kg dog and 1,113 for the 40 kg one — under three times as much for four times the weight.
Then the life-stage factor
Maintenance Energy Requirement multiplies RER by a factor for what the animal actually does. For a 20 kg dog with an RER of 662 kcal:
- Weight loss (×1.0) — 662 kcal
- Senior (×1.4) — 927
- Neutered adult (×1.6) — 1,059
- Intact adult (×1.8) — 1,192
- Active (×2.0) — 1,324
- Puppy or working (×3.0) — 1,986
The spread from weight loss to growth is threefold on the same animal. Choosing the wrong factor is a bigger error than any imprecision in the weight.
Neutering changes the number
Note the gap between neutered and intact — 1.6 against 1.8, about 12%. Neutering genuinely lowers energy requirements, and continuing to feed the previous amount is one of the most common routes to a pet gradually becoming overweight.
The adjustment is worth making deliberately at the time rather than noticing a year later.
Cats are not small dogs
The same formula applies, and the numbers are startlingly small. A 4.5 kg neutered cat needs about 346 kcal a day. A single treat can be a meaningful fraction of that, which is why cats gain weight on what looks like generosity.
It is also why measuring matters more for cats: the margin for error in a 346-kcal budget is much narrower than in a 1,059-kcal one.
From calories to a scoop
Calories are not something you can put in a bowl. The food portion calculator converts the target using the energy density on the label — dry foods usually quote kcal per cup, and the label's metabolisable energy figure gives kcal per kilogram.
A 900-kcal target on a food at 380 kcal per cup is 2.37 cups a day, or about 1.18 cups per meal on twice-daily feeding. Change the food and that number changes, sometimes by a lot: energy density between foods varies enough that the same cup can be a third more or less.
Then feed to the animal, not to the number
The calculation is an estimate and individual metabolism varies considerably around it. The check is body condition: run the body condition score every few weeks and adjust the calories if the score is moving in the wrong direction.
Treats count, and they are the usual reason a carefully calculated ration does not work. A common guideline is to keep treats under about a tenth of daily calories — and to subtract them from the meals rather than adding them on top.
General information, not veterinary advice. Confirm targets, and any weight-management plan, with your vet.
The same dog, four lives
| Weight | Resting (RER) | Weight loss | Neutered adult | Active |
|---|---|---|---|---|
| 5 kg | 234 | 234 | 374 | 468 |
| 10 kg | 394 | 394 | 630 | 787 |
| 20 kg | 662 | 662 | 1,059 | 1,324 |
| 30 kg | 897 | 897 | 1,436 | 1,795 |
| 40 kg | 1,113 | 1,113 | 1,781 | 2,227 |
A 20 kg neutered adult needs about 1,059 kcal a day. The same dog working hard needs 1,324 — a difference of 265 kcal, which is roughly 25% more food for the same animal.
Why resting energy is not the answer
RER is what the body burns doing nothing at all. Everything else — walking, thermoregulating, digesting, being a puppy — is a multiplier on top, and the multiplier ranges from 1 for a weight-loss plan to 3 for a working dog.
That is a threefold spread from one number, which is why a feeding guide printed on a bag cannot be right for every dog of that weight. The bag knows the weight and nothing else.
Neutering changes the number
The neutered factor is 1.6 against 1.8 intact — about 11% fewer calories for the same animal, immediately, and permanently.
Feeding the same amount after neutering is the single commonest route to a gradually overweight pet, and it happens because nothing visible changes on the day. The bowl is the same; the requirement is not.
Turning calories into food
Take the daily figure to the portion calculator with the kcal per cup or per kilogram from the bag. At 1,059 kcal and a typical 350 kcal per cup, that is 3 cups a day, or 1.5 per meal across two meals.
Weigh it rather than scooping it. A cup measured by eye varies by a surprising margin, and over a year that variation is the difference between a stable weight and a slow climb.
Treats count
The usual guidance is that treats stay under 10% of daily calories — about 106 kcal for this dog, which is less than most owners imagine. A single large biscuit can be most of it.
The workable approach is to take the treat allowance out of the meal rather than adding it on top, which keeps the total honest without removing the part of the day the dog enjoys most.
Re-run it when anything changes
A neutering, a new food, a change in activity, a birthday that moves an animal into a new life stage — each changes the requirement, and none of them changes the bowl unless somebody does the arithmetic.
Put the figure into the calculator whenever one of those changes, and weigh the food against the answer rather than scooping it. Those two habits together account for most of the difference between a stable weight and a slow climb.
This is general information, not veterinary advice. Every figure here is a starting point for a conversation with your own vet, who knows the animal in front of them. Anything sudden, painful, or getting worse is a call to a clinic rather than a calculation.