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 (ex: "Must Start On," "Must Finish On"). These can override calculated dates entirely and are the most disruptive to schedule logic.
• Soft constraints limit dates in one direction but still allow logic and float to operate within that boundary (ex: "Start No Earlier Than," "Finish No Later Than"). These are generally safer since they don't fully override the network logic.

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.