A mechanism for displaying the number of the week is fitted to a timepiece movement and includes a starwheel for the weeks including 52 or 53 teeth, and a rocker for the weeks including a flexible finger cooperating with the toothed arrangement of the weeks starwheel upon actuation of the rocker by a driving mobile. The driving mobile is driven by one step per day by the movement and to actuate the weeks rocker once every seven days upon passing from the last day of the week to the first. The driving mobile is a driving starwheel including seven teeth, six being silent teeth which are arranged not to cooperate with the weeks rocker and one tooth is a driving tooth arranged to actuate the rocker once per week upon passing from the last day of the week to the first day of the week.