This paper is about Input-Output Hidden Markov Model (IOHMM) to compute the remaining useful life (RUL) of a system with different operating conditions. Well-known algorithms dedicated to Hidden Markov Model (HMM) are extended to IOHMM. The processing to compute the RUL considering further operating conditions are proposed through an application example. In this paper, a single input and multiple outputs IOHMM is considered, but can be generalized to multiple inputs easily.