A system for calculating a mission of an aircraft by combination of algorithms includes a first path calculation module, configured for calculating an optimal mission path between a geographical point of origin and a geographical destination point as a function of airplane performance, operational mission specifications and a weather context. The first calculation module is configured to determine the optimal path in a manner non constrained by a network of waypoints and/or imposed paths between the waypoints. The system includes a definition module, around the optimal path, an optimization region of the path and a second path calculating module, configured to calculate an optimized path of the aircraft in the optimization region in a manner constrained by a network of waypoints and/or imposed paths between the waypoints.