Project plan is produced during the planning phase. Although planning starts much earlier - even during the concept phase and requirements definition, the plan cannot be finalized until reasonable estimates of schedule and costs are made. The project plan is the formal document that guides execution of a project. Planning occurs through a project, that is, the planning process is dynamic and ongoing and many planning processes will be repeated during the design and execution phases as changes are made in the project. Many problems can occur in a project if insufficient time is spent planning; the purpose of planning is to prevent those problems from occurring. causes of poor planning may include estimates that are poorly done, exception handling that is grossly misunderstood; requirements that are incomplete, changing or not understood; technical complexity that is misunderstood; old code content that is not known; new requirements that are added or sneaked into the plan; dictated constraints; and inadequate time to do a project job. Estimating is the bridge from the work break down structure to planning schedules, costs and resources. The basic process of estimating applies to the wide variety of estimates needed in projects, including time estimates for scheduling