Critical Path Method (CPM)
The Critical Path Method (CPM) is a schedule network analysis technique used to estimate the minimum project duration and determine the amount of scheduling flexibility (float) on the logical network paths within the schedule model.
Explanation
The Critical Path Method is one of the most important techniques in project schedule management. CPM performs a forward pass and a backward pass through the schedule network diagram to calculate four key values for each activity: Early Start (ES), Early Finish (EF), Late Start (LS), and Late Finish (LF). The difference between LS and ES (or LF and EF) is the total float for that activity.
The forward pass calculates the earliest possible start and finish dates for each activity by working through the network from the first activity to the last. The backward pass calculates the latest possible start and finish dates by working backward from the project end date. Activities where ES equals LS (and EF equals LF) have zero float and are on the critical path.
The critical path is the longest path through the network and determines the minimum project duration. Any delay to a critical path activity will delay the project finish date by an equal amount. CPM does not consider resource constraints; it only analyzes the logical sequence and durations. Resource constraints are addressed separately through resource leveling, which may change the critical path.
Key Points
- •Uses forward pass and backward pass to calculate ES, EF, LS, LF, and float
- •Identifies the critical path (longest path with zero float)
- •Determines the minimum project duration
- •Does not consider resource constraints (logic-based only)
Exam Tip
Be prepared to calculate the critical path on the exam. Practice forward and backward passes. Remember: CPM identifies the longest path, not the shortest.
Frequently Asked Questions
Related Topics
Critical Path
The critical path is the longest sequence of activities in a project schedule network diagram that determines the shortest possible project duration.
Float (Total Float and Free Float)
Total float is the amount of time an activity can be delayed from its early start without delaying the project finish date. Free float is the amount of time an activity can be delayed without delaying the early start of any successor activity.
Develop Schedule
Develop Schedule is the process of analyzing activity sequences, durations, resource requirements, and schedule constraints to create the project schedule model for project execution, monitoring, and controlling.
Schedule Compression
Schedule compression is a technique used to shorten or accelerate the project schedule duration without reducing the project scope.
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