The amount of calories a person will burn off on a 30 minute stationary bike ride depends on the persons weight and the pace they're riding the exercise bike at.
If you're a person who weighs 145 pounds and you pedal the stationary exercise bike at a moderate pace then in 30 minutes you'll burn off 231 calories but if you speed up the pedaling pace on the exercise bike and pedal at a vigorous speed then you'll burn off 370 calories during your 30 minute stationary bike ride.