Why puppies and kittens need deworming so often

Almost all puppies and kittens are born with roundworms. The larvae pass from the mother across the placenta in dogs, and in the milk in both dogs and cats, so a newborn puppy can be carrying worms before it has ever been outside. That is why deworming starts at two weeks of age — far earlier than most owners expect — and repeats every two weeks until twelve weeks, then monthly until six months. The two-week interval matters because it matches the worm's life cycle: the medicine kills the adult worms, but larvae that are still migrating through the body survive and mature, so the next dose two weeks later catches them. A single dose is never enough for a puppy or kitten, and neither is a dose given at the wrong interval.

The schedule on this page follows the standard guidance from the European Scientific Counsel Companion Animal Parasites (ESCCAP) and the Companion Animal Parasite Council (CAPC): every two weeks from two to twelve weeks of age, then monthly to six months, then every one to three months as an adult. The adult interval depends on risk: a dog that hunts, eats raw food, or has fleas needs monthly deworming; a low-risk indoor cat may need it only every three months. The helper shows the next step for your pet's age, and the full timeline, so you can see the pattern and why it is shaped the way it is.

Which worms, and why they matter

Roundworms are the most common worms in puppies and kittens: they cause a pot belly, poor growth, vomiting and diarrhoea, and they can infect people — especially children — causing a condition called visceral larva migrans. Hookworms cause anaemia and bloody diarrhoea, and can infect people through the skin. Tapeworms come from fleas and from hunting, and are usually noticed as small white segments around the tail. Whipworms affect dogs and cause chronic diarrhoea. Heartworm, carried by mosquitoes, is a different problem — it lives in the heart and lungs, is often fatal, and is prevented with a monthly preventive rather than a dewormer. Lungworm is an increasing problem in dogs in some areas. The point is that "worms" is not one thing, and the product matters: a medicine that kills roundworms may not kill tapeworms, which is why your vet chooses the product rather than the owner guessing.

Adults, fleas and faecal tests

Adult pets still need deworming, because they pick up worms from the environment, from prey, from fleas and from raw food. The interval is a judgement call: every month for high-risk pets, every three months for low-risk ones. Flea control is part of deworming, because fleas carry tapeworms — a pet with fleas will keep getting tapeworms no matter how often it is dewormed, until the fleas are gone. The most reliable way to know what your pet has is a faecal test: your vet examines a stool sample under the microscope and identifies the eggs. It is cheap, it avoids giving medicine your pet does not need, and it catches worms that a routine dewormer would miss. Many vets recommend a faecal test once or twice a year, especially for pets that hunt or eat raw food.

Common mistakes

The most common mistake is deworming once and assuming the job is done — puppies and kittens need the full series. The second is using a product that does not cover the worm your pet has — always check the label or ask your vet. The third is guessing the dose: dewormers are dosed by weight, and an underdose does not work while an overdose can be dangerous, especially in small puppies and kittens. The fourth is forgetting the mother: a nursing bitch or queen should be dewormed alongside her litter, or she will keep reinfecting them. The fifth is ignoring fleas, which reinfect the pet with tapeworms. The sixth is using a dog dewormer on a cat, or vice versa — some dog products are toxic to cats.

When to see a vet

See your vet if your pet has diarrhoea, vomiting, a pot belly, weight loss, a dull coat, or visible worms or worm segments in the faeces or around the tail. See a vet promptly if a puppy or kitten is lethargic, dehydrated or not eating — a heavy worm burden can be dangerous in a very young animal. Your vet decides the product and the timing for your pet and your area, and this page is a general guide, not a prescription. For the vaccination schedule that runs alongside deworming, use the vaccination schedule helper; for feeding a growing puppy or kitten, the dog food calculator or cat food calculator.