Abstract: A system for determining a level of ketosis of a user includes an acetone detector that includes an inlet for receiving a breath of a user, a sensor for sensing an amount of acetone in the breath of the user, a memory storing calibration values for calibrating sensor data, wherein the one or more calibration values are specific to the acetone detector; and an electronic device comprising programs configured for receiving from the acetone detector measurements of an amount of acetone in breath of a user, receiving from the acetone detector the calibration values, determining a ketosis score based on at least one of the measurements, the calibration values, and predetermined thresholds that are associated with levels of ketosis, wherein the ketosis score is an estimate of a level of ketosis of the user, and displaying the ketosis score to the user.