Critical Path Method (CPM) Deep Dive

Critical Path Method

The Critical Path Method (CPM) is a scheduling technique that identifies the longest path through the project network diagram. This path determines the shortest possible project duration.

Key Concepts

• Activities on the critical path have zero total float — any delay to these activities delays the entire project
• A project can have multiple critical paths (which increases risk)
• The critical path can change as the project progresses
• Schedule compression techniques (crashing, fast tracking) only work on critical path activities

Forward Pass (Calculate ES and EF)

• ES (Early Start) — Earliest an activity can begin
• EF (Early Finish) = ES + Duration
• Start from the beginning; at merge points, take the largest EF

Backward Pass (Calculate LS and LF)

• LF (Late Finish) — Latest an activity can finish without delaying the project
• LS (Late Start) = LF − Duration
• Start from the end; at burst points, take the smallest LS

Float Calculations

• Total Float = LS − ES = LF − EF — How much an activity can be delayed without delaying the project end date
• Free Float = ES(successor) − EF(current) — How much an activity can be delayed without delaying the next activity
• Zero total float = critical path activity

Related Study Resources

• Schedule Management Cheat Sheet
• Process Domain Study Guide
• Topic: Earned Value Management