A utility knife that includes a handle having a blade slot, and a knife blade slidably housed in the blade slot. The knife blade is configured to extend and retract longitudinally from a blade slot opening of the blade slot. A first side of the handle includes a blade adjustment opening that exposes a first side of the knife blade to extend and retract the knife blade. A second side of the handle includes a biasing member that applies a lateral force against a second side of the knife blade to bias the knife blade against the first side of the handle. The first side of the handle includes one or more blade stops that engage the knife blade when biased against the first side of the handle to lock the knife blade at a selectable position.