Cat Calorie Calculator: How Many Calories Your Cat Actually Needs

Poppy is asleep on the radiator. She has been asleep on the radiator since roughly ten this morning, and before that she was asleep on the back of the sofa. At some point this afternoon she will get up, walk eleven feet to her bowl, and then reconsider. She is nine years old, eleven pounds, spayed, a domestic shorthair, and she is mine.

Here is the arithmetic of a cat who does nothing all day, and it surprises nearly everyone I show it to. Poppy needs 234 calories a day. That is exactly her resting requirement. Not her resting requirement plus something for the walking and the reconsidering. Just the resting requirement. The activity surcharge for an indoor cat, in every veterinary source I can find, rounds to zero.

I'm Dana Whitcomb, a certified veterinary technician — twelve years, seven in general practice and five on overnight emergency. That number is the most useful thing on this page, and it explains an enormous number of heavy cats.

Your indoor cat isn't a special case, and that's the point

Calories for indoor cat: the multiplier is 1.0, and that isn't a typo

There is no indoor multiplier. I went looking for one — the search volume says people want one — and it doesn't exist. Not in AAHA's 2021 guidelines, not in the Pet Nutrition Alliance's table, not in Merck. All three fold indoor cats into a single row labelled overweight-prone / inactive, and that row is 1.0 × RER.

Sit with what 1.0 means physically. Your indoor cat's maintenance energy requirement — the number meant to cover living, moving, playing, hunting the hair tie under the fridge — is identical to what she burns lying still in a warm room. The entire activity term is zero. Not small. Zero.

That isn't a rounding convenience. It's what happens when an animal built to hunt several times a night gets a bowl instead, and it's why "she barely eats anything and she's still fat" is one of the most common sentences in a feline exam room. She may well barely be eating anything. Barely anything is the budget. So this tool defaults to the indoor/inactive factor rather than the neutered-adult one — defaulting to 1.2 would quietly hand most of the cats reading this a 20% surplus they never asked for.

The feline arithmetic, in full

The formula is the same one dogs get. RER = 70 × (body weight in kg)^0.75. The resting energy requirement doesn't differ by species — it's a function of metabolic body size, and a 5 kg cat and a 5 kg dog idle at about the same rate. The Pet Nutrition Alliance says so outright: the equation for RER is the same for both. What differs is everything you multiply it by.

Compiled by Paw Charts from AAHA 2021 Box 1, the PNA MER table and Merck — paw-charts.com

Two things worth noticing. First, the numbers everyone repeats — 1.2 neutered, 1.4 intact — sit at the bottom of AAHA's published ranges. That's the opposite of dogs, where the popular figure sits at the top of the band every time. Same guideline, same table, opposite direction, and I've never seen anyone mention it. We use the bottom values and show you the band.

Second, the kitten factor is softer than it looks. AAHA and Merck both give 2.5; the Pet Nutrition Alliance gives 2–3, decreasing from around four months. A flat 2.5 underfeeds an eight-week-old and overfeeds a nine-month-old — there's a slope hidden inside that single number. If you're growing one, the kitten growth chart is the better tool for the job.

Why this cat calorie calculator can't reproduce the WSAVA chart

Because WSAVA isn't using this model at all. If you're a veterinarian cross-checking us against the chart on your wall, this section is why the numbers differ.

Nearly every consumer cat calculator presents RER × factor, and a fair number attribute it to WSAVA. WSAVA's published cat chart doesn't use RER × factor. It uses the NRC 2006 allometric equations directly — and, the part that matters, with different exponents. Lean adult: 100 × BW^0.67. Obese-prone adult: 130 × BW^0.4.

Not 0.75. An RER × factor model can never reproduce that curve, because the shape differs, not just the scale — multiplying 70 × BW^0.75 by any constant will not bend it into 130 × BW^0.4. Expect divergence at the weight extremes and reasonable agreement in the middle. That's structural, not an error to fudge away, and a tool that "matches WSAVA" by tuning its multipliers is telling you a story about its own numbers rather than about your cat.

One more thing a reviewer should know. AAHA and AAFP's 2021 feline life stage guidelines use the linear RER — 30 × kg + 70 — as their default for adult cats. That's defensible: it's valid from 2 to 25 kg and essentially every pet cat lives inside that band. We use the exponential form. The two differ by roughly 1–3% for a normal-sized cat, which is nothing beside the individual variation below — but if our number doesn't precisely match an AAHA/AAFP worked example, that's why. It's all set out on how we calculate.

How wrong can this be? Up to half

Individual cats vary from the calculated number by up to 50% — the Pet Nutrition Alliance's figure and Ohio State's, and it applies to both species. Merck states it as ±30% between any two animals of the same body weight. Nobody credible says ±20%, and the ±50% figure is routinely misattributed to WSAVA, whose charts carry a qualitative caution and no number at all. Which is why Poppy's 234 comes with a range of 117 to 351 bolted to it — an uncomfortable spread for a number people want exact, and the truth. The dog calorie calculator goes further into where that ±50% comes from and why it makes most of the multiplier argument theatre.

Senior cats may need more calories, not fewer

An older cat's requirement is also tangled up with things arithmetic can't see: kidney disease, an overactive thyroid, diabetes. Those drive most of the real "how much should I feed her" questions in cats past twelve, and none of them is a multiplier. The cat age calculator maps the life stages — Poppy at nine is 52 in human years and squarely Mature, which isn't the same as senior and is roughly when I started paying closer attention.

Taking weight off a cat

Cat weight loss calorie calculator: slow is the entire point

The target is 0.8 × RER at your cat's ideal weight. Three sources converge on it — AAHA's 2021 Box 1, AAHA's 2014 weight management guidelines, and the Pet Nutrition Alliance — and the two words doing the work are ideal weight. Not current weight. Every weight-management factor takes the target weight as its input, which is why the field above is required and why the tool refuses to run without it. You feed a percentage of what she should weigh, not of what she does.

Notice that 0.8 is below RER. That's deliberate, and it's the guideline's own default — despite "never feed below RER" being repeated across the internet as a safety rule. For cats that rule is simply wrong.

Hepatic lipidosis, worded correctly

This is where I have to be careful, because the subject gets mangled in both directions.

Hepatic lipidosis is, in Merck's words, "the most common acquired and potentially lethal feline liver disease." Fat gets mobilised out of the body faster than the liver can process it. It sets up, again per Merck, when "a primary disease process causing anorexia or food deprivation" meets an overconditioned cat.

Read that mechanism closely, because the popular version is wrong and the wrong version does harm. The trigger is losing weight too fast, or not eating at all, in a cat who is already heavy. It is not weight loss. Weight loss is the intervention an overweight cat needs, and telling owners "weight loss is dangerous for cats" is both false and an excellent way to talk someone out of the thing that would help their cat. Merck names the failure mode exactly: "forced weight loss with unacceptable food substitutions." That's the crash diet — owner switches to a diet food, cat refuses it on principle, cat effectively fasts. The diet didn't do it. The fasting did.

One figure to actively distrust: the ">25% weight loss" number that circulates as a threshold. It isn't one. Merck lists dramatic weight loss over 25% among the clinical signs of established hepatic lipidosis — a symptom of the disease, not a line you cross to acquire it. Repeating it as a trigger inverts cause and effect. The only quantified risk threshold in a guideline is caloric: below 60% of ideal-weight RER, AAHA says, cats may be at increased risk. This tool never renders a number below 70% of ideal-weight RER, so it cannot take you there.

How fast, really

AAHA's target for cats is 0.5–2% of body weight per week. In practice cats do the lower half of that. Flanagan and colleagues followed 413 client-owned cats through supervised weight-loss programs, and the mean rate achieved was 0.8% ± 0.50 per week. So we project timelines from 0.8%, not from the middle of the band.

The Pet Nutrition Alliance gives a narrower range, 0.5–1%, which genuinely conflicts with AAHA's 0.5–2%. We follow AAHA as the guideline of record, but I'll say plainly what I think that conflict means: 2% a week is a ceiling, never a target. PNA's ceiling happens to sit much closer to what real cats actually do.

And here's the asymmetry I find most useful in this whole section. The safe floor for dogs is 1% a week. For cats it's 0.5% — half. That isn't a rounding difference; it's the guideline acknowledging that the risks run in opposite directions in the two species. A dog losing weight slowly is just a dog losing weight slowly. A cat losing weight slowly is an acceptable outcome. If your cat is creeping down at 0.4% a week and eating happily, that is a program working, not failing. Don't tighten it.

How many calories should a cat eat? Poppy, all the way through

Poppy: 11 lb, spayed, indoor, domestic shorthair, nine years old, still on the radiator.

11 lb is 4.99 kg. RER = 70 × 4.99^0.75 = 234 kcal/day. Indoor and inactive, so × 1.0 → 234 kcal/day. The multiplier does nothing at all. That's the entire indoor story in one line of arithmetic. Honest range at ±50%: 117 to 351.

Now suppose she weren't where she is. Say she were 13 lb and we were aiming at 11. The weight-loss factor runs on the ideal weight, so RER at 11 lb is 234, × 0.8 → 187 kcal/day. She'd have 2 lb to lose, which at the 0.8% a week real cats achieve is about 19 weeks. Not six. Nineteen. That number is deflating and it's the honest one — a tool quoting you nine weeks at 1.5% is handing you research-colony arithmetic and setting you up to quit in month two.

Turning 187 kcal into actual food is its own problem, because cats eat wet, dry or both and the density gap between them is roughly threefold. The cat food calculator does that conversion from your own can or bag rather than from a generic chart.

The body condition detail almost everyone gets wrong for cats

You'll read everywhere that 4–5 out of 9 is the ideal body condition score for dogs and cats alike. That is wrong for cats, and it's a small, sharp, checkable error.

On WSAVA's own charts: the dog chart prints 4 and 5 both under IDEAL. The cat chart prints only 5 under IDEAL — score 4 sits under UNDER IDEAL. Different species, different charts, genuinely different answers, and the cat window is narrower. There's also a footnote on the cat chart worth carrying: "A body condition score of 6/9 may be acceptable in some cats, especially older cats." Which, read next to the senior digestibility point above, is consistent rather than contradictory.

It matters because body condition is the feedback loop the calculator hands off to. Advice to "aim for 4–5" has you targeting a score WSAVA labels under ideal for your cat. Aim for 5 — or better, have your vet score her. It takes ten seconds, and hands beat eyes every time.

Why cats, specifically

As of APOP's 2022 clinical survey — the last one in which veterinary professionals actually scored body condition rather than asking owners for an opinion — 61% of US cats were overweight or obese. APOP's 2023–2025 surveys are opinion polls and get re-reported as prevalence. They aren't, and APOP says so itself.

The comparison with dogs is the interesting part, and it's easy to garble. Cats are less likely than dogs to be merely overweight — 28% against 37% — but substantially more likely to be obese: 33% against 22%. Cats skew to the severe end. Set that beside everything above — slower loss, a lower floor, a liver that punishes fasting — and you arrive at the sentence this page is built around: the species most in need of weight loss is the one where it's most dangerous to rush.

What to do with the number

Feed it for a month. Then put your hands on her — ribs under a thin covering, a waist behind the ribs seen from above, a slight tuck underneath. If she's drifting up, the number was too big for her. If she's dropping faster than about 1% a week, ease off. That loop is the tool. The arithmetic just gives it somewhere to start.

The rest of our dog and cat calculators run on this same engine and the same data file, including the dog age calculator, which is the closest thing on this site to a proper argument about method. If you want portions rather than calories, the cat food calculator is next door. And every formula here is listed with its source and the date I last checked it on how we calculate. I re-verify the whole file against Merck, AAHA and WSAVA every January and July. Catch me there.