Computer-aided design of bearing systems is finding its way into many industrial sectors requiring high reliability and trouble-free performance from rotor/bearing systems. This trend will accelerate as more bearing analysis codes are ported to the personal computer and incorporate user-friendly interfaces. This paper describes and explains the theoretical basis for bearing load rating and life estimating as reflected in such programs. The calculation of individual bearing and system B-10 Fatigue Life and their correlation to the ISO International Standard 281 for dynamic load ratings and rating life is presented. Showing the continuity from the standard methods to the more fundamental computer analysis of bearing systems will allow for a smooth transition from one to the other.Presented at the 47th Annual Meeting in Philadelphia, Pennsylvania May 4-7, 1992