Abstract: Systems and methods are provided for providing a composite stress index representing a quantified stress level that an individual may be experiencing or may have experienced during a time interval of interest. The composite stress index is determined based on a combination of heart beat data representative of cardiac activity of the individual during the time interval of interest and one or both of: sleep history data comprising one or more sleep onset times and one or more awakening times during the time interval of interest; and physical activity history data representative of gross motor activity of the individual during the time interval of interest.