The estimation of the time and cost at completion represents one of the most important concepts in Project Management. Its importance increased a lot when the Navy’s A-12 project of the US Department of Defense (DoD) failed due to cost overruns and time delay. The identification of the best method for the calculation of the Estimate at Completion, thus became one of the major challenges in the evaluation of the acquisition costs in the purchasing process of military weapons. Also today, the determination of the performance factors and the estimate at completion of time and cost of a project is fundamental for the monitoring and control of the project progress and for the implementation of corrective actions, if some problems arise, to bring back the project on time and on budget.