This paper presents a probabilistic approach to guarantee the performance of a real-time system. While traditional real-time system analysis tends to guarantee that each task instance will complete its execution before its absolute deadline (hard guarantee), our approach permits to estimate the probability that it will happen.Such a statistical guarantee is performed based on interarrival and execution times probability distributions, rather than their worst case values. The advantage of a probabilistic approach is a more efficient usage of system resources, allowing to give a certain level of deadline guarantee to task sets that the classical schedulability analysis would reject.