Is weight loss normal in old cats?

No — investigate rather than accept loss as ageing. Senior cats commonly have treatable conditions such as hyperthyroidism or kidney disease that cause weight loss.

Why is my cat losing weight but still eating?

Hyperthyroidism, diabetes, and intestinal disease can cause weight loss despite a good or increased appetite. Blood tests are needed to identify the cause.

Do worms cause weight loss in cats?

Heavy parasite burdens can contribute, especially in kittens or cats not on regular worming. Faecal testing and appropriate worming help identify this.

How much weight loss is concerning?

Any noticeable unintentional loss matters — prominent spine and ribs, or a drop on kitchen scales. Weigh monthly to catch small changes early.

Cat Health

Why Is My Cat Losing Weight UK?

Quick answer

**Unintentional weight loss in cats is not normal** — even if appetite seems unchanged. Common causes include **[hyperthyroidism](/glossary/hyperthyroidism), [diabetes](/glossary/diabetes-mellitus), [kidney disease](/glossary/chronic-kidney-disease), and cancer**. Senior cats over eight need prompt blood tests. Weigh regularly on kitchen scales.

Key takeaways

No — investigate rather than accept loss as ageing. Senior cats commonly have treatable conditions such as hyperthyroidism or kidney disease that cause weight loss.
Hyperthyroidism, diabetes, and intestinal disease can cause weight loss despite a good or increased appetite. Blood tests are needed to identify the cause.
Heavy parasite burdens can contribute, especially in kittens or cats not on regular worming. Faecal testing and appropriate worming help identify this.

The full picture

Causes, home monitoring, treatment options and the exact signs that mean call your vet — in the complete guide.

Read the full guide Check symptoms

Frequently Asked Questions

Is weight loss normal in old cats?: No — investigate rather than accept loss as ageing. Senior cats commonly have treatable conditions such as hyperthyroidism or kidney disease that cause weight loss.
Why is my cat losing weight but still eating?: Hyperthyroidism, diabetes, and intestinal disease can cause weight loss despite a good or increased appetite. Blood tests are needed to identify the cause.
Do worms cause weight loss in cats?: Heavy parasite burdens can contribute, especially in kittens or cats not on regular worming. Faecal testing and appropriate worming help identify this.
How much weight loss is concerning?: Any noticeable unintentional loss matters — prominent spine and ribs, or a drop on kitchen scales. Weigh monthly to catch small changes early.

Reviewed 2026-07-19 against UK veterinary guidance · Information only — not a substitute for seeing your vet.