A system for monitoring wear on a gearbox of a wind turbine, the system comprising: a wind turbine including a rotor, a gearbox, a rotor shaft coupling the rotor and the gearbox, a generator, and a generator shaft coupling the gearbox and the generator; a first sensor configured to detect a parameter indicative of a torque (134, 138) exerted on the rotor shaft or the generator shaft; and a controller communicatively coupled to the first sensor, the controller being configured to determine the torque (134, 138) exerted on the rotor shaft or the generator shaft based on measurement signals received from the first sensor; wherein the controller is further configured to determine a torque exerted on the other of the rotor shaft or the generator shaft based on the determined torque exerted on the rotor shaft or the generator shaft; wherein the controller is further configured to determine a stress value for the gearbox based on the respective torques (134, 138) and rotational speeds (142, 146) of the rotor shaft and the generator shaft; wherein the controller is further configured to assign a positive value to one of the torque exerted on the rotor shaft or the torque exerted on the generator shaft and a negative value to the other of the torque exerted on the rotor shaft or the torque exerted on the generator shaft to account for torque reversals in the gearbox when determining the stress value; wherein the controller is further configured to determine an accumulated wear value based on the stress value; wherein the controller is further configured to monitor a duration during which the gearbox experiences the stress value and determine the accumulated wear value based on the duration of the stress value. a wind turbine including a rotor, a gearbox, a rotor shaft coupling the rotor and the gearbox, a generator, and a generator shaft coupling the gearbox and the generator; a first sensor configured to detect a parameter indicative of a torque (134, 138) exerted on the rotor shaft or the generator shaft; and a controller communicatively coupled to the first sensor, the controller being configured to determine the torque (134, 138) exerted on the rotor shaft or the generator shaft based on measurement signals received from the first sensor; wherein the controller is further configured to determine a torque exerted on the other of the rotor shaft or the generator shaft based on the determined torque exerted on the rotor shaft or the generator shaft; wherein the controller is further configured to determine a stress value for the gearbox based on the respective torques (134, 138) and rotational speeds (142, 146) of the rotor shaft and the generator shaft; wherein the controller is further configured to assign a positive value to one of the torque exerted on the rotor shaft or the torque exerted on the generator shaft and a negative value to the other of the torque exerted on the rotor shaft or the torque exerted on the generator shaft to account for torque reversals in the gearbox when determining the stress value; wherein the controller is further configured to determine an accumulated wear value based on the stress value; wherein the controller is further configured to monitor a duration during which the gearbox experiences the stress value and determine the accumulated wear value based on the duration of the stress value.