Why You Should Weigh Your Pet Every Month

If you only ever track one thing about your pet's health, make it weight.

It is free, it takes two minutes, and it detects a very wide range of serious disease long before anything visible happens. Vets rely on weight trends heavily, and yet most animals are weighed once a year, at their vaccination appointment, if at all.

Why the eye fails

You see your pet every day, which makes you the worst possible person to notice gradual change.

A 30kg Labrador losing 2kg over four months is losing about 1.5% of body weight a month. That is completely invisible to daily observation, and it is also a clinically significant loss that warrants investigation.

The same is true in reverse. Most owners of overweight dogs genuinely do not perceive them as overweight, because the change happened slowly and the reference point moved with it.

The scale doesn't have this problem.

What weight loss can mean

Unexplained weight loss — meaning no diet change and no increase in exercise — is a sign of a long list of conditions:

Chronic kidney disease
Hyperthyroidism (cats)
Diabetes
Cancer
Dental disease causing difficulty eating
Heart disease
Inflammatory bowel disease and malabsorption
Liver disease
Chronic pain reducing appetite
Parasites

The threshold worth knowing: a loss of 5% or more of body weight, without an intentional diet change, warrants a vet visit.

For a 4kg cat, that's 200g. For a 30kg dog, 1.5kg. Those are amounts you will not see by looking.

What weight gain can mean

Usually it means too much food and not enough exercise, and that alone is worth acting on — obesity shortens life, worsens arthritis, and increases anaesthetic and diabetes risk.

But gain can also indicate:

Hypothyroidism in dogs
Cushing's disease
Fluid retention from heart disease or liver disease — this one matters, because fluid accumulating in the abdomen registers as weight gain while the animal is actually losing muscle
Pregnancy
Some tumours

A dog whose weight is stable but whose belly is enlarging while the spine becomes more prominent is not gaining fat. That's a same-week vet call.

How to weigh them properly

Small dogs and cats:

Use a baby scale if you have one — they're accurate to 10g and ideal. Otherwise:

1. Weigh yourself on bathroom scales, note it

2. Pick up the pet, weigh again

3. Subtract

This works but bathroom scales are typically accurate to only 100–500g, which is coarse for a 4kg cat. If you're monitoring a cat closely, a cheap digital baby or luggage scale is a worthwhile purchase.

Some cats will sit on a kitchen scale in a box. Zero the scale with the empty box first.

Large dogs:

Most veterinary practices have a walk-on scale in reception and are entirely happy for you to pop in and use it without an appointment. Just ask. Many practices actively encourage this.
Some pet shops have scales
The lift-and-subtract method works if you can lift them safely

Consistency matters more than precision. Same scale, same time of day, ideally before a meal. A number that's consistently 200g out is still perfectly good for spotting a trend.

How often

Healthy adult pet: monthly
Senior pet (7+ for dogs, 10+ for cats, earlier for large breeds): monthly, minimum
Pet on a weight loss programme: every two weeks
Pet with a diagnosed condition: as your vet advises, often weekly
Growing puppy or kitten: weekly

Pick a date — the first of the month works well — and attach it to something you already do.

Record it

An unrecorded weight is nearly useless. The value is entirely in the trend.

Whatever you use — a note on your phone, a page in a notebook, a chart on the fridge, the community app — record the date and the number. That's it.

After six months you'll have something genuinely valuable: a line. And a line answers the question every vet asks, which is not "what does he weigh?" but "has that changed?"

Weight isn't the whole picture

Weight alone can mislead, particularly in older animals losing muscle while gaining fat, where the number stays flat while body composition deteriorates.

Pair it with body condition scoring — a hands-on assessment:

Ribs: you should be able to feel them easily under a thin layer of fat, without pressing hard. If you have to push to find them, they're overweight. If they're sharply visible, underweight.
Waist: looking down from above, there should be a visible narrowing behind the ribs
Tuck: from the side, the belly should rise from the ribcage towards the hind legs, not hang level

And muscle condition separately — run your hands over the spine, the skull, the shoulder blades and the hips. Muscle loss over these areas is a significant finding even at a stable weight, and it's common in kidney disease, cancer and heart disease.

What to do with a change

Loss of 5% or more with no diet change: book a vet appointment. Bring the numbers.

Steady downward trend over several months, even if each drop is small: book an appointment. Trends matter more than single readings.

Gain, with normal feeding: worth a conversation, particularly if the belly is enlarging.

Rapid change in either direction: sooner rather than later.

When you go, take the actual record. "He's gone from 31.2kg in February to 28.6kg in June, and we haven't changed his food" is one of the most useful sentences an owner can say. It transforms a vague consultation into a focused one, and it frequently prompts the blood test that finds the problem.

The habit

First of the month. Two minutes. Write it down.

That's the whole thing, and it is genuinely one of the highest-value habits available to a pet owner. Our community tracker exists to make it slightly easier — you enter the number, it draws the trend, and it tells you when the line moves in a way that matters. But a notebook works. The habit is the intervention.