How often does a chicken need to be wormed?

Ours are only POL at the moment and came to us wormed but I wondered how often they need to be done so that I can put it on the calendar.

Is there anything else that needs doing to them on a regular basis to keep them nice and healthy (not counting the maintenance of the chicken house).

I worm mine every 3 months as they free range and have a lot of contact where wild birds are but others who keep their birds in a covered run may only do theirs 2 or 3 times a year max