It is an object of the present invention to provide a heart rate monitor system (10) which is able to determine the resting heart rate in an effective and unobtrusive manner. In an aspect of the present invention a heart rate monitor system (10) comprising an inactivity determining unit (320) for determining periods of inactivity (IP) of a user based on motion data (MD) detected by at least one motion sensor (200) attached to the user and a resting heart rate calculating unit (330) for calculating a resting heart rate (RHR) of the user based on heart rate data (HR) detected by at least one heart rate sensor (100) attached to the user during the periods of inactivity (IP) as determined by the inactivity determining unit (320) is provided.
