The life of a wheel bearing unit under real load conditions can now be calculated based on actual load histories. These load histories are recorded over many small but discrete time slices where the speed and loads within each time slice can be regarded as constant. This enables the equivalent load Peqv for each time slice to be evaluated by means of the classical bearing life theory of Lundberg and Palmgren. The relative damage contributed by each time slice is then obtained, and eventually, the overall probabilistic damage from the load histories can be established by accumulating the damage derived from each individual time slice. From the damage distribution, the resultant equivalent load PEQV, representing one/several sets of road recordings, can be evaluated using the Palmgren-Miner rule. This resultant equivalent load is then used to evaluate the bearing life by re-employing the bearing life theory of Lundberg and Palmgren. A computer package has been developed to perform the calculations.