How often should you worm a puppy?

The first thing is how do you know your dog does not have worms?
Worms can be so small you can not see them or their eggs.
We actually worm our dogs to keep them healthy, but also to keep us healthy too.
The only way to absolutley know your dog has no worms is to do serial ( a few ) stool collection and have them tested.
The risk of human contmination is important.
I would advise worming your dog every 3 months with a reputable allwormer every 3 months, costs less than testing and works for dog and all in contact