Generally every four weeks but have moved to every three weeks through the summer.
Would love to get to a stage where I have the same work as this but every four weeks, it is just enough for both me and my customers.
I am 'Northern' and can't see the problem in people wanting their windows cleaned every two weeks, I choose not to as most of my round is spread so would be uneconomical - thats why my customers don't mind me coming round every three weeks.
Its my business and I choose the frequency - only on certain jobs will I justify 6 or 8 weekly. If they don't like it I pass the job on but can safely say this is very rare.