| Applies to |
| Microsoft Office Project 2003 |
You may wonder, "what ultimately determines the length of my project?" The answer is the critical path (critical path: The series of tasks that must be completed on schedule for a project to finish on schedule. Each task on the critical path is a critical task.), which is the series of tasks (or even a single task) that dictates the calculated finish date of the project in Project path and the resources assigned to them will help ensure that your project finishes on time.
What does the critical path show about your project?
What is a critical task?
How does Project calculate the critical path?
How do I shorten the critical path?
Can I see multiple critical paths?
Can I see the critical path across multiple projects?
What does the critical path show about your project?
By knowing and tracking the critical path for your project, as well as the resources assigned to critical tasks (critical task: A task that must be completed on schedule for the project to finish on time. If a critical task is delayed, the project completion date might also be delayed. A series of critical tasks makes up a project's critical path.), you can determine which tasks can affect your project's finish date and whether your project will finish on time.
This sequence of tasks has no slack (slack: The amount of time that a task can slip before it affects another task or the project's finish date. Free slack is how much a task can slip before it delays another task. Total slack is how much a task can slip before it delays the project.), and therefore drives the finish date of the project. All tasks in this sequence are on the critical path and are called critical tasks. In the Detail Gantt view, critical tasks appear in red.
This sequence of tasks does not drive the finish date of the project, and therefore the tasks are not critical. In the Detail Gantt view, noncritical tasks appear in blue.
Total slack is the amount of time this sequence of tasks can slip before it affects the finish date of the project. In the Detail Gantt view, total slack appears as a thin teal line.
If it's important for your project to finish on schedule, pay close attention to the tasks on the critical path and the resources assigned to them. These elements determine whether your project will finish on time.
A series of tasks is generally interrelated by task dependencies (task dependencies: A relationship between two linked tasks; linked by a dependency between their finish and start dates. There are four kinds of task dependencies: Finish-to-start [FS], Start-to-start [SS], Finish-to-finish [FF], and Start-to-finish [SF].). Although there are likely to be many series of interrelated tasks in your project plan, the series of tasks that will finish the latest is the project's critical path.
Note The critical path can change as critical tasks are completed or as tasks in another series of tasks are delayed.
What is a critical task?
Tasks that cannot be delayed without affecting the project finish date are the critical tasks. In a typical project, many tasks have some slack and can therefore be delayed a little without delaying other tasks or affecting the project finish date.
As you modify tasks to resolve overallocations (overallocation: The result of assigning more tasks to a resource than the resource can accomplish in the working time available.), adjust costs, or revise scope (scope: The combination of all project goals and tasks, and the work required to accomplish them.), be aware of the critical tasks and that changes to them will affect your project finish date. Critical tasks make up the schedule's critical path.
A task becomes critical when it meets any one of the following conditions:
A task stops being critical when it's marked as completed, because it then can no longer affect the completion of successor tasks or the project finish date.
How does Project calculate the critical path?
Project defines critical tasks as those that have no slack. However, you can change when a task becomes critical. For example, you can make a task critical if it has one or two days of slack. This is helpful if you want to be alerted to tasks becoming critical when you still have a day or two of buffer.
Slack is determined by the early finish (early finish date: The earliest date that a task could possibly finish, based on early finish dates of predecessor and successor tasks, other constraints, and any leveling delay.) and late finish (late finish date: The latest date that a task can finish without delaying the finish of the project. It is based on the task's late start date, as well as the late start and late finish dates of predecessor and successor tasks, and other constraints.) dates of the tasks in your schedule. An early finish date is the earliest date that the task could finish, based on its start date and scheduled duration. A late finish date is the latest date that the task can finish without delaying the project finish.
The difference between early finish and late finish dates determines the amount of slack. For critical path tasks (tasks that have no slack), the early finish and late finish dates are identical.
How do I shorten the critical path?
If you want to bring in the project finish date (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.), you need to bring in the dates of your critical path tasks. This is also known as crashing (crash: To decrease a project's overall duration without changing task relationships. Crashing a project typically requires assigning additional resources to tasks.) a project. To do this, you can:
- Shorten the duration or work on a task on the critical path.
- Change a task constraint to allow for more scheduling flexibility.
- Break a critical task into smaller tasks that can be worked on simultaneously by different resources.
- Revise task dependencies to allow more scheduling flexibility.
- Set lead time between dependent tasks where applicable.
- Schedule overtime.
- Assign additional resources to work on critical path tasks.
Note If you bring in the dates of your critical path, a different series of tasks could become the new critical path.
There is always one overall critical path for any project schedule. The new critical path would then become the series of tasks you track more closely to ensure the finish date you want.
Tip If you bring in the finish dates of the critical path and another series of tasks does not overtake it, then you can successfully bring in the finish date of the project as a whole.
Can I see multiple critical paths?
By default, Project displays only one critical path, the one overall critical path that affects the plan's finish date. You can set up your project plan to see multiple critical paths for each independent network or series of tasks. You might find this useful if you are working with a master project and you want to see the critical path for each subproject. This is also useful if the project is broken into multiple phases (phase: A group of related tasks that completes a major step in a project.) and you want to see the critical path for different phases or milestones (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.).
When viewing multiple critical paths (multiple critical paths: A series of tasks that must be completed on schedule for a project to finish on schedule. Identify and track multiple critical paths to be more effective in managing conditions that could affect your project's finish date.), remember that there's still one overall critical path whose finish date affects the project's finish date.
Tip Changing the finish date for any of the secondary critical paths will probably not change the project's finish date.
Can I see the critical path across multiple projects?
If you are working with multiple projects (multiple projects: Several project plans that may or may not be linked or consolidated. If you are working on several projects at one time, you can compare information about critical paths, resource sharing, or priorities among all of the projects.), cross-project links (cross-project links: Dependencies between tasks in different Project files, also called external dependencies. Project plans do not need to have a master project-subproject relationship to include a cross-project link.), or subprojects (subproject: A project that is inserted into another project. Use subprojects as a way to break complex projects into more manageable parts. Also known as an inserted project.), you can see the overall critical path. Subprojects can be treated as summary tasks for Project to calculate the overall critical path.
