An apparatus and method are disclosed for determining movement information for a user that carries an accelerometer whilst moving. The apparatus receives acceleration data from the accelerometer that are defined relative to a frame of reference of the accelerometer. A transformation is determined and applied to the acceleration data or to data derived from the acceleration data to determine acceleration data is a frame of reference of the user that includes a direction of travel of the user and a side to side direction transverse to the direction of travel of the user. The acceleration data or data derived from the acceleration data is analysed to determine a time period corresponding either to a stride period or to a step period of the user as the user is walking or running; and information about accelerations in the side to side direction are used to disambiguate whether the determined time period corresponds to the stride period of the user or to the step period of the user.