An electrical box extender for repositioning an electrical box level with a newly installed wall surface. The box extender is a one-piece device including a frame member with rearward-extending sidewalls and corner members extend. A peripheral flange extending along the outer edge of the frame member includes an outward extending end flange. End flanges include an outer edge and side edges with the side edges including a plurality of paired side notches therein. Each paired side notch is in axial alignment with a plurality of slots extending along the end flange. A row of axially-aligned slots are aligned with an associated pair of side notches. Each row of axially-aligned slots and their associated notches defines breakaway flange portion on the end flange. The breakaway flange portions can be left intact or removed as needed for mounting of either a standard, mid-size, or max-size cover plate.