The life time of a wind turbine / wind farm can be extended by checking for continued operation after the design life has expired. Conditional for life time extension is the proof that the wind turbine can continue to be operated safely in the future and that structural integrity is guaranteed in accordance with current regulations. We analyze the type certificates and check whether it continues to meet the applicable guidelines after the designed life time has expired. The procedure also applies to wind turbine types whose manufacturers no longer exist. The process for evaluating and validating the life time extensions of wind turbines is divided into an analytical part (determining the remaining useable life time of components) and a practical part (on-site inspection) and thus follows the "principles for carrying out an evaluation and verification of life time extension for onshore wind turbines” by the German Wind Energy Association (BWE). The result of the analysis is explained in an expert opinion and the life time extension confirmed in a certificate. The analytical part calculates when the load-bearing components reach the limits of their service life. The loads that actually occur are compared with the loads under design conditions for which the manufacturer has designed the system and its components, and the remaining service life is calculated there from. Downtimes, yield results and operation times are also included in the calculations. The basis for the simulation of the site loads is a turbulence report, which is to be provided for the analysis. In this way, loads resulting from possible continued operation and the loads according to the design conditions can be simulated. With this method and our experience, the life reserve of the wind turbine can be precisely analyzed component by component and the period for safe continued operation can be determined. According to the principle of the ‘weakest link in the chain’, additional possibilities for component replacement are shown.