We study the magnetic behavior of the metallic system-FeHx as a function hydrogen concentration (x). Using ab-initio density functional theory, we investigate the effect of hydrogen on the stability of magnetic configurations considering two antiferromagnetic (AFM) phases and a ferromagnetic (FM) one present in epsilon-Fe (AFM-I and AFM-II). Our results show a magnetic transition induced by H between AFM and FM around x = 0.44. In this way, two main effects can determine the stability and the magnetic phase transition: a volume increase that produces an AFM to FM transition and the charge transfer effect from H to Fe energetically favors the FM phase. We discuss these behaviors in detail and physically explain the magnetic transition and the overall behavior using a phenomenological Stoner model for these systems.