The invention relates to a method for formulating the strategy of an aircraft, with a view to favouring adherence to a time constraint.With this aim, the method according to the invention consists in optimizing the margin available for the formulation of the aircraft's speed strategy, by calculating a first target required time of arrival (RTAtarget) which is higher, respectively lower, than the required time of arrival (RTA), in the case where said required time of arrival (RTA) is greater, respectively less, than the mean estimated time of arrival (ETAmean). According to the invention, the first target required time of arrival (RTAtarget) is used for the formulation of the aircraft's speed strategy. According to the invention, a second target required time of arrival (RTAtarget2) can be determined subsequently, and used for the formulation of the speed strategy, with the aim of utilizing the margin, previously optimized, available for the formulation of the aircraft's speed strategy.