Systems and methods of recommending replacement of parts on machines. In one embodiment, a method of recommending replacement includes receiving data for a part type, determining a cumulative probability function for an infant mortality of the part type, and determining a cumulative probability function for a natural life of the part type. The method includes defining a lower time boundary and an upper time boundary between which the part type is considered operative. The lower time boundary is defined at a time point at an intersection between the cumulative probability function for the infant mortality and the cumulative probability function for the natural life of the part type. The upper time boundary is defined at a time point representing an estimated end of an operative life of the part type. Recommending replacement of a part on a machine may then be determined based on the upper and lower time boundaries.