The honest answer is that it depends on the household, not the sofa. A retired couple with a wool three-seater in a formal front room and a family of five with two dogs and a cream corner unit are not on the same schedule, and pretending otherwise helps nobody.
But there is a clear principle underneath: the longer soil sits in a fabric, the more of it becomes permanent, and the more the fibre wears.
A rough schedule by household
Family home with children or pets: every twelve months. This is the group that gets the most obvious value, because the soil load is high and it accumulates faster than anyone notices.
Couple or single occupant, moderate use: every eighteen months to two years. Body oils still build on head rests and arm tops even without heavy traffic, and they are the marks that become permanent if left.
Shared house or rental: at every tenancy change, and more often if the sofa is in constant use. Landlords who clean at changeover get more years out of furniture, and it is a fraction of the cost of replacing it.
Allergy household: every six to twelve months, and the reason is dust mites and their waste rather than visible soil. Hot water extraction removes a large proportion of what accumulates in upholstery, which visible cleanliness tells you nothing about.
Why waiting costs more
Soil in fabric is abrasive. Every time someone sits down, grit moves against fibre, and that wear is cumulative and permanent. A sofa cleaned regularly keeps its texture; one cleaned every six years has physically worn fibre that no process restores.
Bound soil is harder to release. Body oils oxidise over time and bond progressively more tightly, so a three-year build-up takes longer to shift than three separate annual cleans — and a proportion of it will not shift at all.
And the result is less satisfying. A sofa cleaned annually looks essentially new afterwards. One cleaned after six years looks dramatically better than it did, which is not the same thing. We would rather tell you that before you book than have you be disappointed after.
What to do between cleans
Vacuum weekly with an upholstery tool, including into the crevice between the seat and the arm. Most of what damages fabric is dry grit, and vacuuming removes it before it can abrade anything. This is genuinely the highest-value thing you can do.
Rotate and flip loose cushions monthly so the wear spreads rather than concentrating in one seat. It also keeps the filling in better shape.
Deal with spills immediately, and correctly: blot with a dry white cloth, no rubbing, no washing-up liquid, no heat. A spill blotted properly in the first minute is usually a non-event.
Keep it out of direct sunlight where you can. UV fades upholstery and weakens natural fibres, and a faded panel is not something cleaning can reverse.