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.
Primavera P6 Constraint: Start On or After - Pushes the activity’s early start date to the constraint date
Pushes the activity’s early start date to the constraint date

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.
Primavera P6 Constraint: Start On or Before - Pulls the activity’s late start date to the constraint date
Pulls the activity’s late start date to the constraint date

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.
Primavera P6 Constraint: Start On - Shifts both the activity’s early and late start date to the constraint date
Shifts both the activity’s early and late start date to the constraint date

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.
Primavera P6 Constraint: Finish On or After - Pushes the activity’s early finish date to the constraint date
Pushes the activity’s early finish date to the constraint date

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.
Primavera P6 Constraint: Finish On or Before - Pulls the activity’s late finish date to the constraint date
Pulls the activity’s late finish date to the constraint date

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.
Primavera P6 Constraint: Finish On - Shifts both the activity’s early and late finish date to the constraint date
Shifts both the activity’s early and late finish date to the constraint date

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.
Primavera P6 Constraint: As Late as Possible - Pushes early dates as late as possible
Pushes early dates as late as possible

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.

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