Constraints

Constraints are imposed start or finish dates that override normal schedule logic and float calculations (ex: “Must Finish On” or “Start No Earlier Than”).

Hard vs. Soft Constraints 

• Hard constraints lock an activity's date regardless of logic or float. The schedule is forced to honor the date even if predecessors finish early or late. These can override calculated dates entirely and are the most disruptive to schedule logic.
  • Mandatory Start/Must Start On: Activity must begin on an exact date
  • Mandatory Finish/Must Finish On: Activity must end on an exact date 
• Soft constraints limit dates in one direction but still allow logic and float to operate within that boundary. These are generally safer since they don't fully override the network logic.
  • Start On/ Finish On: Target date, but schedule logic can push it out
  • Start/Finish No Earlier Than: Earliest date a task can begin/end
  • Start/Finish No Later Than: Latest date a task can begin/end

How constraints affect the schedule:

• Overusing constraints can force the schedule into unrealistic timelines.
• It reduces flexibility, potentially causing resource bottlenecks.
• Constraints can mask underlying scheduling issues by hiding true dependencies.

Best Practices:

• Apply constraints sparingly, only when absolutely necessary (ex: regulatory deadlines, contractual milestones).
• Rely on logical relationships to drive the schedule whenever possible.
• Regularly review constraints to ensure they remain relevant and do not conflict with progress.