Why no single schedule fits everyone
A carpet in a flat where one person is out all day lives a very different life from one in a house with five children and visitors every evening. The number of feet, meals and spills is simply not comparable.
So treat any figure as a starting point, then adjust it by what you see, smell and feel when you run your palm over the pile.
As a rule, cleaning before the carpet is heavily soiled is easier on you and gentler on the fibres than cleaning after years of build-up, because deep soil needs longer extraction and may not all come out.
