A baseline (baseline plan: The original project plans [up to 11 per project] used to track progress on a project. The baseline plan is a snapshot of your schedule at the time that you save the baseline and includes information about tasks, resources, and assignments.) is the set of original start (start date: The date when a task is scheduled to begin. This date is based on the duration, calendars, and constraints of predecessor and successor tasks. A task's start date is also based on its own calendars and constraints.)and finish dates (finish date: The date that a task is scheduled to be completed. This date is based on the task's start date, duration, calendars, predecessor dates, task dependencies, and constraints.), durations (duration: The total span of active working time that is required to complete a task. This is generally the amount of working time from the start to finish of a task, as defined by the project and resource calendar.), work (work: For tasks, the total labor required to complete a task. For assignments, the amount of work to which a resource is assigned. For resources, the total amount of work to which a resource is assigned for all tasks. Work is different from task duration.), and cost (cost: The total scheduled cost for a task, resource, or assignment, or for an entire project. This is sometimes referred to as the current cost. In Project, baseline costs are usually referred to as "budget.") estimates that you save after you've completed and fine-tuned your project plan but before the project begins. It is the primary reference point against which you measure changes in your project. In addition, a baseline saves nearly 20 pieces of information, including totals and timephased (timephased: Task, resource, or assignment information that is distributed over time. You can review timephased information in any available time period in the fields on the right side of the Task Usage and Resource Usage views.) information for tasks (task: An activity that has a beginning and an end. Project plans are made up of tasks.), resources (resources: The people, equipment, and material that are used to complete tasks in a project.), and assignments (assignment: A specific resource that is assigned to a particular task.). You can save up to 11 baselines.
Because the baseline provides the reference points against which you compare actual project progress, it should include your best estimates for task duration, start and finish dates, costs, and other project variables you want to monitor. Baseline information that consistently differs from current data shows that your original plan is inaccurate. Typically, this difference occurs if the scope or nature of the project has changed. If project stakeholders (stakeholders: Individuals and organizations that are actively involved in the project or whose interests may be affected by the project.) agree that the difference warrants it, you can modify or rework the baseline at any time during the project. You may find saving multiple baselines especially useful for long projects, or projects in which scheduled tasks or costs have changed dramatically and your initial baseline data is no longer relevant.
An interim plan (interim plan: A set of task start and finish dates that you can save at certain stages of your project. You can compare an interim plan with the baseline plan or current plan to monitor project progress or slippage. You can save up to 10 interim plans.) is a set of current project data that you save after the project begins and compare against the baseline to assess project progress. An interim plan saves only two pieces of information, the current task start and finish dates. You can save up to 10 interim plans. If you need to take snapshots of extensive project data during the planning phase, save multiple baselines. For example, you may want to do this at major planning milestone (milestone: A reference point marking a major event in a project and used to monitor the project's progress. Any task with zero duration is automatically displayed as a milestone; you can also mark any other task of any duration as a milestone.). Then if you need to save just task start and finish dates after the project begins, you can save multiple interim plans. For example, you may want to do this monthly or quarterly.