The bottom line on Evolutionary Delivery is that, whether or not it reduces overall development time, it provides tangible signs of progress that can be just as important to rapid development as all-out development speed. It might appear that this incremental approach takes longer than a more traditional approach, but it almost never does because it keeps you and your customer from getting too far out of touch with your real progress.

Evolutionary Prototyping has been reported to decrease development effort by from 45 to 80 percent (Gordon and Bieman 1995). Staged Delivery, on the other hand, does not generally reduce development time, but it makes progress more visible. The specific reduction in development time that you experience from Evolutionary Delivery will depend on the specific mix of Evolutionary Prototyping and Staged Delivery that you use.