Vet at FirstVet answers:
The worming protocol varies depending on the age of the cat and the wormer used. Cats that spend a lot of time outdoors and hunt should be wormed more frequently.
It is recommended to start de-worming kittens when they are between 4 and 6 weeks old and then at 8 weeks and 12 weeks of age. After that they should be wormed monthly until 6 months of age. Once 6 months old, worming can continue as recommended for adult cats which is every 3 months, or monthly if the cat is an active hunter.
Indoor cats do not need to be de-wormed. However, if there are mice around and your cat catches them you should de-worm your cat against tapeworm.
There are lots of different worming products available. Always ensure you use a worming product made for cats. If you are confused regarding the treatment protocol you should ask a veterinarian for advice.