P6 supports the following types of activity constraints:
Start On: Imposes the specific start date you select. The Start On constraint can delay an activity's early start or move forward an activity's late start to satisfy the constraint date.
Start On or Before: Defines the latest date an activity can start. This constraint only affects late dates and can decrease total float. When calculating a schedule, P6 imposes the start on or before constraint in the backward pass only if the calculated late start date will be later than the imposed date.
Start On or After: Defines the earliest date an activity can begin. This constraint affects only early dates. When calculating a schedule, P6 imposes the start on or after constraint in the forward pass only if the calculated early start date will be earlier than the imposed date.
Finish On: Imposes the specific finish date you select. The Finish On constraint can delay an activity's early finish or move forward an activity's late finish to satisfy the constraint date.
Finish On or Before: Defines the latest time an activity can finish. The finish on or before constraint affects only late dates.
Finish On or After: Defines the earliest date an activity can finish. The finish on or after constraint reduces float to coordinate parallel activities, ensuring that the finish of an activity is not scheduled before the specified date. It is usually applied to activities with few predecessors that must finish before the next phase of a project.
As Late As Possible: Imposes a restriction on an activity with positive float to allow it to start as late as possible without delaying its successors. When calculating a schedule, P6 sets the activity's early dates as late as possible without affecting successor activities. This option disables the calendar icon.
Mandatory Start: Imposes the early and late start dates you select. P6 uses the mandatory early start date regardless of its effect on network logic. A mandatory early start date could affect the late dates for all activities that lead to the constrained activity and all early dates for the activities that lead from the constrained activity.
Mandatory Finish: Imposes the early and late finish dates you select. P6 uses the mandatory finish date regardless of its effect on network logic. This constraint affects the late dates for all activities that lead to the constrained activity and all early dates for the activities that lead from the constrained activity.