Late Dates
The latest possible dates a task can start and finish
Late dates are calculated in the backwards pass.
Late dates cannot be calculated for a task path (a set of tasks connected by dependencies) that doesn’t eventually lead to a Milestone.
Late Start
late_start
The latest date a Task can start is based on when its dependents are finished or started, depending on the dependency type (series or parallel).
Late Finish
late_finish
The latest date a Task can finish is based on when its dependencies are finished and its duration.
Milestones
Unlike Tasks, Milestones have a single early_date field. This is the soonest a Milestone can occur.
Legacy CPM
In legacy CPM, Milestones have an Early Start and an Early Finish, but depending on the type, only one is used.