Abstract: It is very important to find the optimal software development cost along with release timeduring the software development process. Therefore, in this study, we analyze and predict software development cost and release time using NHPP reliability models. As a result first, the cost curves of all models proposed in this study decrease at the initial stage but gradually increase at the latter stage when the release time passes. Second, prior to software release, if the cost of testing per unit time and the cost of removing one defect found during the testing process increased, the development cost also increased but the release time remained unchanged. Third, after the software release, if the cost of correcting the faults found by the operator increases at the operating stage, the development cost is reduced but the release time is delayed. Fourth as a result of comparing the models applied in this study, Lindley Model is the best model because it has high reliability for mission time in the future, low cost of software development and quick release time. Through this study, we were able to present software developers and operators with the necessary prior information to predict the economic software development cost and the optimal software release time.