Mark the cut line with a pencil and straightedge
Wear safety glasses, a dust mask, and gloves
Score the cement board with a carbide-tipped utility knife
Snap the board along the scored line
Cut through the back side with the utility knife if needed
Use a jigsaw with a carbide or cement-board blade for curves or openings
Use a circular saw with a cement-board blade for long cuts
Cut outdoors or in a well-ventilated area
Support the board firmly on a flat surface
Vacuum dust after cutting