Why Is My Cat Losing Weight?

Call your vet now if

• Your cat has stopped eating, or has eaten very little for more than a day
• There is repeated vomiting or diarrhoea, or any blood in either
• Your cat is weak, hiding and unwilling to move, or seems very flat
• You notice fast, laboured or open-mouthed breathing
• Your cat has lost weight quickly, over days or a couple of weeks, and looks noticeably thinner
• Your cat is drinking a great deal more and also seems unwell
• You see yellowing of the gums, the whites of the eyes or the skin of the ears

If you are not sure how urgent it is, phone your vet or an out-of-hours service and describe what you have noticed.

Why weight loss matters in cats

Cats are small, and a loss that looks minor on the scales can be a meaningful share of their body weight. A few hundred grams on a cat can be similar in proportion to several kilograms on a person. Cats are also very good at carrying on as normal while unwell, so a gradual drop in weight may be the only outward sign for some time.

That is why vets treat unexplained weight loss seriously. It is not a diagnosis, but it is a signal worth investigating, and many of the conditions behind it are easier to manage when they are found early.

Why it is so easy to miss

Weight loss in cats often creeps up slowly. You see your cat every day, so gradual changes are hard to spot. A thick or long coat can hide a thinning frame, and cats who are less active may lose muscle along the spine and back legs before anything looks different from a distance.

Signs that might prompt you to look more closely include:

• Feeling the spine, hips or shoulder blades more sharply when you stroke your cat
• A narrower look from above, or a loss of the gentle curve over the back
• A collar that seems looser
• A coat that looks dull, unkempt or greasy, often because grooming has dropped off
• Changes in appetite, either eating less or seeming hungrier than usual

Our guide to healthy weight and body condition explains how to feel for body condition with your hands, which is a useful habit alongside weighing.

How to weigh your cat at home

Regular weighing is the most reliable way to catch a change early. Once a month is a good routine for most adult cats, and more often if your vet suggests it.

The carrier method works well with ordinary bathroom scales:

1. Weigh the empty carrier and write down the figure.
2. Put your cat in the carrier and weigh it again.
3. Subtract the first figure from the second. The difference is your cat's weight.

An alternative is to weigh yourself, then weigh yourself holding your cat, and subtract. Bathroom scales are not always precise for small changes, so the carrier method with digital kitchen or baby scales can be more accurate if your cat will tolerate it.

A few tips help keep readings consistent:

• Weigh at roughly the same time of day, ideally before a meal
• Use the same scales each time
• Write the figure down straight away with the date

Recording each monthly weight in Petopedia lets you see the trend over time and show your vet a clear picture, which is often more helpful than a single number on the day of the appointment. You may also find the tools on our pet calculators page useful for context.

Possible causes need a vet to sort out

There are many reasons a cat might lose weight, and they range widely. Some relate to how much food is going in, such as dental pain making eating uncomfortable, a change in food, or competition with another pet at the bowl. Others relate to how the body is using that food, which is where conditions affecting digestion, hormones, the kidneys or other organs may come in. Parasites, stress and changes at home can also play a part.

Because the possibilities are so varied, it is not something to try to work out alone. Your vet will usually examine your cat, check their weight against previous records, look in the mouth and may suggest blood and urine tests. Bringing your home weight log, along with notes about appetite, drinking, toileting and behaviour, can make that visit more productive.

Eating well but still losing weight

It can be tempting to feel reassured if your cat is still eating heartily. In fact, a cat who is eating normally or even more than usual, yet losing weight, is just as much a reason to see your vet. A good appetite alongside weight loss can be a sign that the body is burning through energy faster than it should or not absorbing food properly.

Other things worth mentioning to your vet include increased thirst, which we cover in why is my cat drinking so much, restlessness, vocalising at night, and any change in litter tray habits.

If your cat is eating less, see why is my cat not eating. Cats should not go without food for long, so a poor appetite combined with weight loss should be checked promptly.

Older cats

Weight loss is particularly common in middle-aged and senior cats, and it can be easy to put down to just getting older. While some older cats do lose a little muscle, a steady downward trend is still worth investigating. Many conditions that affect older cats respond well to care when they are picked up early.

For older cats, more frequent weighing and regular senior health checks are a good idea. Our guide to caring for a senior cat has more on what to watch for.

What you can do now

• Weigh your cat today so you have a starting figure
• Write down what and how much your cat eats each day, and whether any food is left
• Note any changes in thirst, toileting, grooming or energy
• Make sure each cat in a multi-cat home can eat in peace without being pushed away
• Avoid changing food or starting supplements before your vet visit, unless advised, so the picture stays clear
• Book a vet appointment, and bring your notes

If you are unsure how quickly to act, our guide to signs your pet needs a vet can help. Noticing weight loss early is one of the most useful things you can do for your cat, and you are already doing it by paying attention.