Calibration is the alignment of between a clinician’s perceived and actual diagnostic accuracy. In this randomized study, pre-clerkship medical students diagnosed chest x-rays and rated their confidence in the diagnosis. The control group received no feedback, one group received performance (accuracy) feedback, and one group received additional information on why the diagnosis was correct or not. Students in both intervention groups showed increased confidence, accuracy, and calibration in comparison to those in the control group. These results suggest feedback is an effective method to improve calibration.