Due to the rising share of renewable energy sources, reinforcements in the transmission grid have become necessary. As the approval of grid investments is time consuming, investments are planned about ten years in advance. Possible developments of the future energy system are usually covered by a set of scenarios. Currently in Germany an optimal grid development plan is determined for each scenario. This leads to the question of which investments out of which grid development plan should be built. This paper presents a stochastic planning approach, taking into account all scenarios in order to determine a final grid development plan. The method is applied for four scenarios of the German transmission grid in the year of 2025. The results of the new method shows the value of a stochastic planning algorithm relative to using the scenario optimal development plans as a base for the final decision of reinforcements.