Linear actuator comprising • a reversible DC-motor , which through a transmission drives a spindle and thus applies a linear movement to a spindle nut retained against rotation, where the spindle nut is connected to an activation element , which can be displaced between two end positions on the spindle , • an electric control, • a housing surrounding the components of the actuator , and • a positon detection system for determining the position of the spindle nut on the spindle, wherein the position detection system is encased in the housing and further comprises • at least one magnetic sensor arranged in a position on a length parallel to the axial direction of extent of the spindle and • a magnet arranged in connection with the spindle nut or the activation element , characterized in that the position detection system determines the position of the spindle nut on the spindle by counting rotations of a movable element in the actuator, whose movement relates to the rotations of the spindle , and indicating the position of the spindle as a counter value on a scale describing the dynamic range of the possible displacement of the activation element , and in that the position detection system is further configured to • receive and process a signal from the at least one magnetic sensor , where the signal indicates a known position of the spindle nut during its travel on the spindle , and • subsequently calibrate the counter value of the position detection system such that it corresponds to a predetermined counter value of the known position of the spindle nut during its travel on the spindle . • a reversible DC-motor , which through a transmission drives a spindle and thus applies a linear movement to a spindle nut retained against rotation, where the spindle nut is connected to an activation element , which can be displaced between two end positions on the spindle , • an electric control, • a housing surrounding the components of the actuator , and • a positon detection system for determining the position of the spindle nut on the spindle, wherein the position detection system is encased in the housing and further comprises • at least one magnetic sensor arranged in a position on a length parallel to the axial direction of extent of the spindle and • a magnet arranged in connection with the spindle nut or the activation element , characterized in that the position detection system determines the position of the spindle nut on the spindle by counting rotations of a movable element in the actuator, whose movement relates to the rotations of the spindle , and indicating the position of the spindle as a counter value on a scale describing the dynamic range of the possible displacement of the activation element , and in that the position detection system is further configured to • receive and process a signal from the at least one magnetic sensor , where the signal indicates a known position of the spindle nut during its travel on the spindle , and • subsequently calibrate the counter value of the position detection system such that it corresponds to a predetermined counter value of the known position of the spindle nut during its travel on the spindle . <EOS>