a self - loading utility knife including an elongate handle having an internal chamber defining an axis and at one end is flat aperture for the passage of an active blade . the flat aperture defines a cutting plane extending through said handle along the axis . a blade - holder is slidably mounted in the chamber for movements in directions along the axis and is adapted to secure a single active blade for movement through the aperture when the blade holder is in the extended position . a blade - holder release button is coupled to the blade holder and is slidingly movable relative to the handle to move blade holder between retracted and extended positions . the handle has a blade compartment which is open to the chamber and can receive a stack of spare blades when a cover to the compartment is opened and blades can be shifted transversely relative to the axis into the chamber . the blade holder is provided with a recess having a depth no greater than the thickness of one blade to allow at least a portion of a single blade to be received in a retaining relationship within the recess to cause an end - most blade in the stack to be received within said recess to follow the movements of the blade holder . a spring biases the blades in the blade compartment inwardly in the direction of the blade holder . a blade releasing disc on the blade holder selectively locks a blade to the blade holder when the blade holder is in the extended position . the blade holder only receives a single blade within the recess . a belt clip s provided on the compartment cover .