Primavera P6 Constraint: How does it work?

1. Purpose of Constraints in Primavera P6

• Date restrictions used to reflect project requirements that cannot be built into the network logic.
• More accurately reflect real-world aspects of a project.
• Provide added control of a project.
• Apply to the entire project or to individual activities.
• Commonly used project-level constraint: Must Finish By
• Commonly used activity-level constraint: Start On or After
• No more than 10 percent of a project’s activities should be constrained.

2. Constraint Type

Must Finish By

• Used when an overall project deadline must be met.
• Forces all activities in the project to finish by the date (and time) specified.
• Establishes the date from which late dates are calculated in the backward pass.
• Affects the Total Float of the entire project.

Start On or After

• Used to set the earliest date an activity can start.
• Forces the activity to start no earlier than the constraint date.
• Pushes the activity’s early start date to the constraint date.
• Affects the early dates of the activity’s successors.

Start On or Before

• Used to set the latest date an activity can start.
• Forces the activity to start no later than the constraint date.
• Pulls the activity’s late start date to the constraint date.
• Affects the late dates of the activity’s predecessors.

Start On

• Forces the activity to start on the constraint date.
• Shifts both the activity’s early and late start date to the constraint date.
• Affects the early dates of the activity’s successors and the late dates of the activity’s predecessors.

Finish On or After

• Used to set the earliest date an activity can finish.
• Forces the activity to finish no earlier than the constraint date.
• Pushes the activity’s early finish date to the constraint date.
• Affects the early dates of the activity’s successors.

Finish On or Before

• Used to set the latest date an activity can finish.
• Forces the activity to finish no later than the constraint date.
• Pulls the activity’s late finish date to the constraint date.
• Affects the late dates of the activity’s predecessors.

Finish On

• Forces the activity to finish on the constraint date.
• Shifts both the activity’s early and late finish date to the constraint date.
• Affects the early dates of the activity’s successors and the late dates of the activity’s predecessors.

As Late as Possible

• Delays activity as late as possible without delaying successors.
• Pushes early dates as late as possible.
• Also called a zero free float constraint.

Mandatory Start and Finish

• Forces early and late dates to be equal to the constraint date.
• May violate network logic.
• Affects the early dates of the activity’s successors and the late dates of the activity’s predecessors.