A lot of whether or not a software project is successful depends on management capability of project managers. Therefore, EVA (Earned Value Analysis) has received a lot of attention recently as a method for managing a project in an integrated fashion by introducing a unified metric called EV (Earned Value) and quantitatively measuring and analyzing the cost and schedule of a project. Project managers can use EVA to estimate SEAC (Schedule Estimate At Completion) and EAC (Estimate At Completion). However, there are several constraints inherent in a software development plan, and any software development plans have to satisfy the constraints. Therefore, SEAC and EAC are estimated by using EVA and by taking account of the constraints,, and the estimation result by the former is compared with the estimation result by the latter. As a result, it turns out that EVA quite often generates inaccurate estimations for SEAC and EAC. In this way, this paper clarifies problems of a method for estimating SEAC and EAC by EVA.