Dog Weight Loss: How to Monitor It and What to Tell Your Vet

Gradual weight loss in dogs is one of the most reliably missed symptoms in veterinary medicine. Not because owners don't care, but because the change happens slowly - a few grams a week, a slight softening of the muscle definition around the hindquarters - and when you see your dog every single day, you adjust to their new shape without registering it as a change.

The owners who catch it earliest are almost always the ones who weigh their dog regularly and write it down. The PDSA PAW Mini Report 2025 found that 82% of UK dog owners are unaware of their dog's body condition score - a measure that reflects both underweight and overweight states - making regular owner-led weigh-ins one of the most practical health monitoring habits available.

Why photos aren't enough

Most people notice weight loss in dogs retrospectively - they look at a photo from six months ago and think, oh. The problem with using photos as your monitoring system is that you're looking backward. A weight log gives you a current number to compare against a previous one, which is much more useful.

It also gives you something specific to take to a vet appointment. "I think she's lost some weight" is a starting point. "She was 28 kg in January, she's 25.5 kg now" is actionable information.

How to weigh your dog at home

You don't need a special scale. If your dog is small enough to carry, step on bathroom scales holding the dog, then weigh yourself alone - the difference is your dog's weight.

For larger dogs, most vet practices will let you come in for a weigh-in without an appointment. Many also have scales in reception. Some larger pet shops have scales in their pet care sections. It takes five minutes and the information is worth having.

Aim for monthly weigh-ins, at the same time of day, before a meal. Consistency in conditions makes the comparison more meaningful.

What counts as significant weight loss

The threshold that most vets take seriously is around 10% of body weight. For a 30 kg dog, that's 3 kg - achievable through gradual loss that you might not notice by eye.

That said, context matters. A 3 kg loss in a dog on a prescribed weight-management diet is the goal. The same loss in a dog who wasn't trying to lose weight warrants investigation.

A useful rule: if your dog has lost 5% or more of their body weight in three months without a deliberate dietary change, mention it at your next vet visit. If it's 10% or more, book an appointment rather than waiting.

Causes worth knowing about

Many of the conditions that cause weight loss have dedicated monitoring guides: diabetes, inflammatory bowel disease, cancer, dental disease, arthritis, and obesity and weight management.

Weight loss can indicate a wide range of conditions - which is why the pattern around it matters as much as the number.

Inadequate intake is the obvious first check. Is the dog actually eating all their food? Has anything changed about appetite, or how they approach their bowl? A dog who's losing weight because they're eating less is different from one who's eating normally but losing weight anyway.

Dental disease is one of the most commonly overlooked causes of reduced food intake. A dog with a painful mouth may eat inconsistently, drop food, or favour one side. They won't tell you their teeth hurt - you'll notice it through appetite changes and weight loss if you're tracking. The PDSA identifies dental disease as the most common health condition in adult UK dogs, affecting the majority of dogs over three years old - meaning dental pain should always be considered when unexplained appetite reduction and weight loss occur together.

Gastrointestinal conditions including inflammatory bowel disease, chronic pancreatitis, and parasites can impair nutrient absorption even in a dog who appears to be eating normally. Weight loss alongside recurring digestive symptoms - intermittent diarrhoea, vomiting, or visible discomfort after eating - points here.

Diabetes mellitus causes weight loss despite a normal or increased appetite, because the body can't use glucose properly. Dogs with diabetes typically drink and urinate much more than usual. If weight loss is accompanied by increased thirst, this combination warrants prompt veterinary assessment.

Hyperthyroidism is rare in dogs (unlike cats, where it's common), but it does occur and can cause weight loss alongside increased appetite and restlessness.

Cancer - particularly lymphoma, gastrointestinal tumours, and cancer affecting the liver - commonly presents as unexplained weight loss. This is one reason why unexplained weight loss in a middle-aged or older dog should be investigated rather than attributed to ageing.

Chronic pain or mobility issues can contribute to muscle wasting, which changes body composition even if overall weight stays similar. A dog who's less active due to arthritis may lose muscle mass while maintaining body fat.

What to tell your vet

The more specific you can be, the more useful the appointment. Come prepared with:

• Current weight and previous weights (with dates)
• Whether appetite has changed
• Whether water intake has changed
• Any other symptoms: vomiting, diarrhoea, increased urination, lethargy, coughing
• Anything that changed around the time the weight loss started - new food, new medication, any stressful events

A vet who has a clear timeline and specific numbers can run targeted investigations. A vet who's starting from "she seems lighter lately" is doing more guesswork.

Frequently Asked Questions

My dog looks fine - is gradual weight loss really worth worrying about? Yes. Many dogs with significant underlying conditions look and behave normally until the disease is well advanced. Weight loss is often the first measurable signal. Catching it early and investigating promptly changes outcomes for a number of conditions.

How accurate do home weigh-ins need to be? Accurate enough to track a trend. If you always weigh in the morning before breakfast, using the same scale, you'll get consistent results even if the absolute number isn't perfect. The trend matters more than whether the scale is perfectly calibrated.

Can older dogs lose weight just from ageing? Some muscle loss (sarcopenia) is expected in senior dogs. But significant or progressive weight loss in an older dog shouldn't simply be attributed to age - many causes of weight loss in older dogs are treatable, and the underlying condition should be identified.

My dog has been on a diet and is losing weight - should I still track it? Yes, and this is actually the ideal use case. Tracking your dog's weight during a dietary programme tells you whether it's working, at what rate, and when you've reached the target. Pup Notes tracks weight as a trend over time, which makes this easy to see at a glance.