A sofa bed is convertible to a bunk bed using a base frame assembly; an upper bunk assembly to be disposed on the base frame assembly in a seating position and to be disposed above the base frame assembly in a bunk bed position; a front link and a rear link pivotally attached to the base frame assembly and the upper bunk assembly, alternative embodiments adding a flange plate secured to the rear link with a motor, cable, drive, screw and drive assembly, or adding a torsion spring assembly, or substituting vertical scissors mechanism for the links or substituting telescoping supports for the link assemblies.