It is important that the life of flexible energy equipment be accurately assessed, as knowledge about the pace of life reduction can aid in optimizing the operating conditions for long- and short-term planning purposes. This paper describes a method for assessing the change in life of a gas turbine with start/stop cycles and working in off-design modes. The method was applied to several cases of gas turbine equipments from manufacturers and research companies. As an example, calculations of three different loading modes for a week are presented. This method could also be applied to steam turbines and equipments with combined cycles.