2.3 Critical Path Method & Float Analysis

🎯 Key PMI PMP® Exam Takeaways

• The Critical Path is the longest continuous sequence of dependent activities in the schedule network and has zero total float.
• Any delay to an activity on the critical path directly delays the overall project completion date.
• Total Float (LS - ES or LF - EF) is the amount of time an activity can be delayed without delaying the project finish date.
• Free Float is the time an activity can be delayed without delaying the early start of any immediate successor.

The Critical Path Method (CPM) is the cornerstone of predictive schedule analysis. By modeling project activities, durations, and dependencies in a network diagram, CPM determines the minimum possible duration of the project and calculates schedule flexibility for every activity.

Calculating CPM requires two passes: the Forward Pass computes Early Start (ES) and Early Finish (EF) dates moving from project start to finish; the Backward Pass computes Late Finish (LF) and Late Start (LS) dates moving from finish to start.

Float (or slack) defines activity scheduling flexibility. Total Float is calculated as Late Start minus Early Start (or LF - EF). The path with zero total float is the Critical Path. Free Float measures how much an activity can slip without impacting the early start of its immediate successor.

⚠️ Common PMI Exam Traps

• Assuming the critical path has positive float; by definition, the standard critical path has zero total float.
• Confusing Finish-to-Start dependencies with Finish-to-Finish; FF dependencies dictate that the successor cannot finish until the predecessor finishes.