Scheduling Fundamentals
Milestone
A milestone is a zero-duration schedule activity that marks a point in time, such as a contractual date or the completion of a phase, rather than a piece of work.
Definition
In Primavera P6 a milestone is either a Start Milestone or a Finish Milestone. Because it has no duration it consumes no time itself, but it can carry logic and constraints, which is why finish milestones are commonly used to anchor the project's completion date and to measure float against a contract date. A milestone with a hard constraint can override the dates the logic would otherwise produce, so constrained milestones deserve attention in any schedule review.
Example
A 'Substantial Completion' finish milestone has a predecessor from the last piece of work and no successors; its early finish date is the forecast completion date of the project.