Is my dog or cat overweight? How to tell, and why it matters more than it looks

Excess weight is the commonest preventable health problem in pets, and the hardest for an owner to see, because it arrives a few grams at a time over years and the animal you look at every day never seems to change.

It's worth getting past that blind spot, because a lean pet lives measurably longer and more comfortably than a heavy one — the studies that have followed dogs for life put the difference at around two years. This isn't about appearance; it's one of the few things within your control that changes how long you get.

Why the scales are not enough

A number on its own means little without a breed and a frame to read it against, since a healthy weight for one Labrador is overweight for another of the same breed with lighter bones.

Weight is useful for tracking change in one animal over time, but for the question of whether a pet is the right size, the body itself is the better instrument.

The hands-on test

Vets score body condition on a nine-point scale, and you can do the core of it at home with three checks.

Run your hands along the ribs: you should feel them easily under a thin layer, the way the back of your hand feels through skin, without having to press. Look down from above: there should be a visible waist, a narrowing behind the ribs rather than a straight or bulging outline. Look from the side: the belly should tuck up behind the ribcage, not hang level or sag. If you can't feel the ribs without pressing, there's no waist from above, and the belly doesn't tuck, the pet is carrying too much — and the same three checks work on a cat, where a swinging belly pouch and no felt ribs tell the same story.

One caveat on cats: the loose flap of skin along a cat's lower belly, the primordial pouch, is normal anatomy and not fat. It swings when the cat trots and it's there on lean cats too. Judge a cat by its ribs and its waist, not by that.

The honest version of this test is that it takes the emotion out of it. You aren't judging how the animal looks, which is where affection and habit mislead you; you're feeling for ribs and a waist, which are either there or they aren't.

Why we don't see it

It's worth naming the reasons, because knowing them is most of the cure.

Gradual change is invisible. A dog putting on a few percent a year looks the same every morning, and by the time it's noticeably heavy you've been looking at that shape for so long it reads as normal. Photographs from three years ago are often a shock for exactly this reason.

What's around you shifts the baseline too. If most of the dogs at the park are heavy, a heavy dog looks standard, and a genuinely lean one looks underfed — owners of fit working dogs get asked whether they're feeding them often enough. Breed pictures don't help either; a good many show dogs carrying more than they should.

And the emotional wiring is against you. Food is how most of us express affection, the animal is enthusiastic about it, and refusing is unpleasant in a way that giving isn't. It's also easy to read begging as hunger when it's usually just learned behaviour — a dog that gets something when it stares has been taught to stare.

Why extra weight does real harm

Carried weight isn't inert.

It loads the joints and brings on or worsens arthritis, it strains the heart and airways, it makes an animal overheat sooner in warm weather, and it's bound up with diabetes in cats and with a shorter life across the board. A heavy pet is also a pet in more day-to-day discomfort than its owner realises, because the stiffness and the breathlessness come on so gradually that they read as simply getting older or slowing down, when some of it's the weight and would lift if the weight did.

A few consequences are worth spelling out. Anaesthesia carries more risk in a fat animal, which matters the day it needs a dental or an emergency operation. A heavy cat can't groom its own back and rear, so the coat mats and the skin suffers. An overweight dog tires on walks, so it gets walked less, which makes it heavier — the loop that does most of the damage. And weight makes almost every other diagnosis harder, because abdomens are difficult to feel through fat.

Taking it off safely

Weight comes off through slightly less food and slightly more movement, but the details matter and crash dieting is genuinely dangerous — a cat dropped onto too little food too fast can develop a serious liver condition, so a cat's weight loss in particular should be planned with your vet rather than improvised.

Start by measuring meals with proper scales instead of a scoop, and account for treats, which are where most of the hidden calories live: the biscuits, the chews and the scraps can quietly make up a large part of the day's intake, and the simplest single change many pets need is honesty about them.

Then make it a household decision rather than a personal one. Write down who feeds what, put the day's treat allowance in a jar so nobody double-counts, and agree that the answer to begging is attention rather than food. A diet undone by one person in the house is the commonest reason these plans fail, and it's rarely deliberate.

Add movement in a form the animal can actually do. For a heavy dog that means more short walks rather than one long one, on soft ground, building up gradually — and swimming or hydrotherapy if the joints are already sore. For a cat it means play: two short wand-toy sessions a day, food scattered or hidden so it has to be hunted, and a puzzle feeder instead of a bowl. A cat that's made to work slightly for its food eats more slowly and moves considerably more.

Expect it to be slow. Something in the region of one to two percent of body weight a week is the usual target, which on a small animal is a genuinely small number, and a plan that produces visible change in a month is going too fast. Weigh every couple of weeks and plot it, because the graph keeps you honest when the mirror doesn't.

Two existing pieces do the arithmetic this article only points at: how much to actually feed starts from the dog rather than the label, and the ten-percent rule covers where the extra calories hide. Weigh the pet every couple of weeks as you go, aim for slow steady loss rather than fast, and if the weight won't shift on a genuinely reduced ration, that's a conversation with the vet, because a handful of medical conditions cause weight gain and need ruling out.

Keeping it off

The harder half, and the one nobody plans for.

A pet that has reached a good weight needs a new ration set for that weight rather than a return to the old one, and it's worth asking the vet what that number is at the final weigh-in rather than guessing. Neutering, ageing and the arrival of winter all lower energy needs without lowering appetite, so the portion is something to revisit rather than set once.

Keep weighing, monthly, for as long as you have the animal. Most practices will let you use their scales without an appointment, and a nurse-run weight clinic is often free. Catching a kilogram is easy; catching five is a project — and the whole point of doing this once is not having to do it again.