VolumeThe biggest single factor. A studio is not a T3, and boxes count as much as furniture.
Stairs and liftsFour floors without a lift can add an hour or more. It is counted before you book, never charged on the day.
DistanceWithin Lisbon it barely registers. Cascais, Sintra or crossing to the south bank add a fixed distance component you see upfront.
PackingFull packing adds roughly 15–20% to the move, and saves you the week before it.
Day of the weekMonday to Thursday is 10% cheaper. Weekends are in demand, and moving midweek is the easiest saving there is.