An hour of Indoor Cycling can burn 800 - 1,000+ calories. It is one of the best weight loss & weight maintenance activities around given its high-calorie scorch potential and low-impact nature (i.e. it doesn't pound on your joints).
Best of all, how much you burn is completely up to you. While instructors provide targets and cues, riders ultimately control their own speed and tension. Since there's not a bunch of choreography to worry about, training intensity is individualized allowing new and seasoned riders to workout as one, energize each other throughout class, finish together and benefit from the power and motivation of a team.
Indoor Cycling (i.e. spinning) on a regular basis can also improve heart and lung performance in addition to reducing the risk of certain diseases such as diabetes, coronary heart disease and some cancers.