CPM Key Terms

CPM scheduling uses a handful of core terms, such as activities, durations, logic ties, float, and the critical path, to explain how work connects and moves across a project. This section gives you the essentials so you can read and build a CPM schedule with confidence.

Term	Definition
Actual Start/Actual Finish	The real dates when an activity began and ended, used to update schedule progress.
Activity	A task or piece of work in the schedule that consumes time and resources.
Activity ID	A unique identifier assigned to each task in the schedule.
Activity Type	Categorization of an activity, such as milestone, level of effort, or task.
Baseline	The approved version of the project schedule, used as a reference for tracking progress.
Baseline Start/Finish	Planned start and finish dates captured in the approved baseline schedule.
Calendar	Defines working and non-working time (holidays, weekends, shifts).
Constraint	A restriction placed on an activity’s start or finish (e.g., “Start No Earlier Than”).
Critical Path	The longest chain of dependent activities with zero float; determines the earliest project completion date.
Crew Logic	Sequencing activities based on available resources (e.g., one crew moves from task to task).
Data Date	The “status date” in a schedule; the point in time when progress is recorded and future work is forecasted.
Actual Percent Complete	How complete the project is according to the latest schedule update
Finish-to-Finish	A logic tie where one activity must finish before another can finish.
Finish-to-Start	A logic tie where one activity must finish before another can start.
Total Float (Slack)	The amount of time an activity can be delayed without affecting the project end date.
Free Float (Slack)	The amount of time an activity can be delayed without affecting its successor activities.
Lag	A duration added to a logic tie between two activities (e.g., drywall must cure for 2 days before painting starts).
Logic	The relationships between tasks that establish sequence and drive the critical path.
Milestone	A marker that represents a key event or deliverable.
Near-Critical Path	Activities with float values just above zero (often less than 10 days) that are high risk.
Planned Percent Complete	The percentage of work scheduled to be completed by a given date according to the baseline schedule.
Schedule Performance Index	A measure of schedule efficiency: Actual Percent Complete divided by Planned Percent Complete
Schedule Quality	A measure of the reliability of a schedule, based on best practices and quality checks.
Start-to-Finish	A logic tie where one activity cannot finish until another activity has started (least common relationship).
Start-to-Start	A logic tie where one activity cannot start until another activity has started.
Work Breakdown Structure (WBS)	A hierarchical framework in CPM construction that breaks a project into phases, deliverables, and activities to organize scope and guide scheduling.