The invention relates to a method for optimizing the fuel consumption of an aircraft during flight. At a given point of the flight, a fuel excess (EXTRA) is determined relative to the statutory loads depending on the flight profile and weather conditions forecast for the rest of the flight. If the excess (EXTRA) is less than a given value (EXTRA-mini), for at least one of the forthcoming flight phases ({circle around (1)}, {circle around (2)}, {circle around (3)}), the speed of the aircraft is adjusted so as to increase the excess (EXTRA).