A milestone in a construction schedule is a significant event or completion point that marks meaningful progress. Milestones have no duration themselves; they represent a moment when something is verified complete or a state transition occurs. Common milestones include mobilization, framing complete, drywall complete, MEP rough complete, paint complete, substantial completion, and certificate of occupancy.
Milestones serve three purposes. First, they make schedule progress legible to non-construction stakeholders (owners, lenders, tenants). Second, they often trigger billing events in a milestone-based progress billing schedule. Third, they create checkpoints for schedule reviews where slip can be detected early. Owner-visible milestones are typically a subset of internal scheduling milestones because too many milestones in customer-facing communication creates noise.