The official 5th bedroom is on the lower level.  It's currently being used as an office but could easily become a bedroom, especially given the full bath nearby.  There is an additional room across the hall that lacks the 2 forms of egress appropriate to a bedroom.  In addition, on the 2nd floor, the master sitting room could be converted to a bedroom easily - there is an additional doorway that is prepped (behind drywall) with direct access to the hallway.