A window shade cutter includes an elongated tubular shade holder which is clamped onto a rolled shade, and an elongated tubular collar which is rotatably coupled to the shade holder. A guillotine cutter subassembly is supported on the collar which defines a guide supporting a blade holder and cutting blade in an enclosed fashion. The shade cutter is preferably mounted on a rolled shade at the point of manufacture and packaged as a unit therewith.