Software Engineering includes an important and complex problem of Software cost estimation. Software cost estimation has failed, in most cases, to accurately predict the actual costs or the time needed to develop the system. Project managers have the responsibility to make accurate estimations of cost and effort, but without good software cost estimation tools, the effectiveness of software project management is reduced. A good software cost estimation model can significantly help software project managers make informed decisions on how to manage resources, control and plan a project, and deliver a project on time, on schedule, and on budget. A goal of project managers is to guide to completion a software development project. A successful software development project will deliver to the users a system desired by the customers. If the people that financially support the software development and the users of the software are satisfied, the system can be considered successful. Part of the desired system could be parameters such as: total system development cost, scheduled delivery date, functionality, and quality.