This book offers new mathematical models for software project planning methodologies, including approaches like PMI, IEEE-CS, and Scrum. It also presents a unique hybrid model that combines the IEEE-CS approach with the Scrum one. It introduces the importance of software project planning and goes into detail about the initiation and preparation phases. It covers methods for identifying and analyzing software requirements, creating core project plans, and integrating sub-plans. Additionally, it discusses software project planning using PMI, IEEE-CS, Scrum, and the hybrid approach, and provides practical case studies for each model. This structured approach gives readers a comprehensive understanding of software project planning practices, from traditional to agile approaches, and prepares them to effectively plan and manage software projects using various strategies. Based on these models, interested corporations can develop new Software Project Planning Tools to automate their software project planning function.