You earn "active minutes" when you wear your Fitbit while doing cardio workouts and high-intensity activities like jogging and running. Note that your active minute count will be lower for activities that are not primarily step-based, such as weight lifting, cycling, and rowing.
By default, you are given a starting goal of 30 active minutes a day based on the Center for Disease Control's recommendation of 20-30 minutes of daily moderate-to-intense activity. You can always change your very active minutes goal to meet your personal needs.
All Fitbit trackers calculate active minutes using metabolic equivalents (METs). MET is a unit used to represent the amount of oxygen used by a body during physical activity; therefore, MET can be used as an indicator for intensity of physical activities. For example, a MET of 1 indicates a body at rest. Active minutes are earned for all minutes above a certain MET value based on the thresholds we have established. Simply put, active minutes correlate to a greater amount of activity over the course of 60-second intervals.