The invention relates to a method for capturing in real-time the gaze of a user (P) on a screen (13) of a computing device (12a; 12b; 12c), using an external device (16) with a camera and a computing device (12a; 12b; 12c). The calibration of the system (10) comprises: retrieving at least one gaze estimate (g) of at least one eye of the user from the external device (16); retrieving the corresponding point-of-regard (s) on the screen of the computing device as a 2d pixel coordinate (s) on the screen, retrieving an initial guess on the screen coordinate system (SCS prjor ), and computing parameters of a screen coordinate system (SCS) with an iterative process in which said screen coordinate system (SCS) parameters are initialized by said initial guess on the screen coordinate system (SCS prjor ). Capturing the gaze of a user (P) on the screen of the computing device in real-time comprises: retrieving a gaze ray (d) of the user (P) with the external device defined in the coordinate system (ECS) of said external device, and intersecting the gaze ray (d) of the user (P) with the screen of the computing device, as a function of the ECS and SCS parameters, to capture the gaze-on-screen in real-time.