Being a very efficient and clean energy converter, a proton exchange membrane fuel cell may be utilized to power an electrical vehicle efficiently. Nevertheless, degradation mechanisms affect the lifespan of this electrochemical converter. Consequently, the estimation of the State of Health and Remaining Useful Life have been the subject of numerous researches in the past years. However, most of the methods available considering fuel cell prognostic do not allow the uncertainty quantification of the estimation that can be implemented online considering the calculation cost. As a novelty, the present article depicts a prognostic algorithm based on an Extended Kalman Filter. This observer estimates the State of Health, the speed of the degradation and also provides the estimation uncertainty. Then, an Inverse First Order Reliability Method computes the Remaining Useful Life with a 90% confidence interval based on the estimation of the observer. This method is applied on a 175 hours data set subsequent of an experiment on an 8-cells fuel cell stack that was subjected to an automotive power profile.