Reinforcement corrosion is attracting research interest in many areas due to the economical consequences of the damage generated by the process. Several proposals can be found on prediction of the time to reinforcement corrosion and service life duration. In present communication a proposals is made on using the electrical resistivity to calculate both the initiation and propagation periods. For the time to corrosion onset, the electrical resistivity represents the porosity and its connectivity and therefore can be used to model transport processes. Due to the reaction of chlorides and carbon dioxide with cement phases, the resistivity has to be factorised by a “reaction factor” accounting for it. Concerning the propagation period, the electrical resistivity is an indication of the moisture content of concrete and therefore, it has a certain relationship with the corrosion cement. The service life can be expressed with the following equation: Based in it, minimum resistivity values can be established according to cover thickness and in function of exposure classes.