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.
Leave a Reply