According to COCOMO model the cost of the requirement phase is typically about 6% of the total project cost. Consider a project whose total effort requirement is estimated to be 50 person-months. For this project, the requirement phase consumed 3 person months. If by spending an edition 50% effort in the requirement phase. We reduce the total requirement change request by 33% then the total effort due to rework will reduce from 10 to 20 person months to 6 to 12 person months, resulting in total saving of 5 to 11 person months, i.e. a saving of 10 to 20 % of total cost