According to one embodiment of the present invention, an electronic method for estimating a quantity of spare parts needed for a machine is disclosed. The machine includes a number of replaceable part populations. The method includes receiving (1) life data for a number of part populations in the machine and (2) a duration for the life cycle of the machine. The method further includes calculating a failure distribution according to a failure distribution model for each of the number of part populations based on the life data and calculating an estimated replacement part quantity for each of the number of part populations for one or more time intervals in the duration based on the failure distribution.