A method (100) for monitoring an individual's (710) cardiac activity, the method including the steps of: (i) obtaining (110), during a calibration phase, ECG data for the individual from a ECG monitor； (ii) obtaining (120), during the calibration phase, cardiac activity data for the individual from a wearable device including a plethysmographic sensor； (iii) obtaining (130), during a monitoring phase, cardiac activity data for the individual from the wearable device including the plethysmographic sensor； (iii) generating (140) calibration data from the ECG data and cardiac activity data obtained during the calibration phase； and (iv) calibrating (150), using the calibration data, the cardiac activity data obtained by the wearable device during the monitoring phase.
