Short answer: twice a week for carpeted areas in an average household, and every second day in high-traffic paths if you have pets or someone with allergies.
That is more often than most people vacuum, and the reason is not appearance.
Why frequency matters more than you would think
Vacuuming is not primarily cosmetic. Carpet fibre is damaged by grit, not by feet, the fine abrasive particles that come in on shoes work down into the pile and cut the fibres every time someone walks over them.
Once grit is at the base of the pile, no domestic vacuum reliably lifts it out. So the useful frequency is "often enough that grit never gets down there", which is a shorter interval than "often enough that the carpet looks fine".
Vacuum regularly and carpet lasts years longer. That is the actual argument.
A realistic schedule
| Area | Frequency |
|---|---|
| Entrances and hallways | 2–3× per week |
| Living areas | 2× per week |
| Bedrooms | Weekly |
| Under furniture | Fortnightly |
| Edges and skirtings | Monthly, with the crevice tool |
| Mattresses | Every 2–3 months |
| Upholstery | Monthly |
The four things that change the answer
Pets. Double everything. Hair aside, pets bring in far more outdoor grit than people do.
Allergies or asthma. Vacuum every second day in the rooms used most, and use a machine with a sealed HEPA system, an unsealed vacuum redistributes fine particles rather than removing them, which is worse than not vacuuming.
Shoes indoors. A shoes-off household needs roughly half the vacuuming of a shoes-on one. A decent doormat at every external door is the cheapest cleaning equipment you can buy.
Carpet colour and pile. Deep pile hides grit and needs more. Dark carpet hides dust and gets neglected accordingly.
Technique, briefly
Slow passes beat fast ones, the machine needs time to lift material from the pile, and most people move about twice as fast as they should. Two slow passes in different directions beat six quick ones.
Check the bag or bin at half full, not full. Suction falls off long before it looks full. And empty the machine outside if anyone in the house has allergies.
Hard floors
Vacuum before mopping, always, mopping over grit just moves it around and scratches the finish. Weekly is fine for hard floors in most homes, more in kitchens. Details in how often should you mop your floor.