About Critical Path Activities

Critical path activities are project tasks that must start and finish on time to ensure that a project ends on schedule. A delay in any critical path activity will delay completion of the project, unless the project plan can be adjusted so that successor tasks finish more quickly than planned. Critical activities can be one of two types: float and longest path.

Float is a measure of schedule flexibility. The application uses the Critical Path Method (CPM) to generate a project schedule. This method calculates four dates for each activity in the project plan: Early Start, Late Start, Early Finish, and Late Finish. If the Early Start date and Late Start date for an activity are the same, the activity is said to have zero float. Activities that have zero float must start on time to prevent the schedule from slipping. When an imposed finish date creates a schedule that is shorter than the duration calculated to complete the activities on the critical path, a project has negative float. A project with negative float is behind schedule.

To meet the specific requirements of your project, you can specify the float tolerance used to identify activities as critical. For example, in some situations you might want critical activities to be those with zero or negative float. In other situations, activities with float of three days or less might be identified as critical.

Longest path defines the sequence of driving activities that determine the project end date. Longest path calculation includes interproject relationships. Therefore, activities designated as on the longest path might change depending on whether you schedule a project alone or with its related projects. If a project has interproject relationships and you schedule it alone, the interproject relationships are treated as scheduling constraints. The longest path is broken when activities are no longer driven by relationships; that is, when activity dates are driven by constraints or resource leveling.

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