What the estimate assumes
Each room starts from a typical time for a first full pass: sorting, removing what leaves, and returning what stays. A lightly cluttered room takes about 60 percent of that, a packed one about 160 percent. Extra helpers cut the time, but with diminishing returns, because sorting decisions cannot be fully shared. The range shown is plus or minus 25 percent, since sentimental items and paperwork reliably run long.
Treat the result as a planning aid. If the number looks daunting, that is useful information: it tells you to split the project into sessions rather than wait for a free weekend. Decluttering one room without feeling overwhelmed and deciding what to keep, donate, or discard cover how to run each session.