Real-time systems are a set of programs, a scheduling policy and a system architecture, constrained by timing requirements. Most of daily embedded devices are real-time systems, e.g. airplanes, cars, trains, spatial probes, etc. The time required by a program for its end-to-end execution is called its response time. Usually, upper-bounds of response times are computed in order to provide safe deadline miss probabilities. In this paper, we propose a suited re-parametrization of the inverse Gaussian mixture distribution adapted to response times of real-time systems and the estimation of deadline miss probabilities. The parameters and their associated deadline miss probabilities are estimated with an adapted Expectation-Maximization algorithm.