Critical Path Method
A project scheduling technique identifying the longest sequence of dependent tasks.
Also known as: CPM, Critical Path Analysis, CPA
Category: Techniques
Tags: project-management, planning, scheduling, techniques, dependencies, optimization
Explanation
The Critical Path Method (CPM) is a project scheduling algorithm that identifies the sequence of tasks that determines the minimum project duration. Any delay in critical path tasks directly delays the entire project.
Core concepts:
**Critical Path** - The longest sequence of dependent tasks from project start to finish. It represents the shortest possible project duration.
**Float/Slack** - The amount of time a task can be delayed without affecting the project end date. Critical path tasks have zero float.
**Dependencies** - Relationships between tasks:
- Finish-to-Start (FS): Task B starts when A finishes
- Start-to-Start (SS): Tasks begin together
- Finish-to-Finish (FF): Tasks end together
- Start-to-Finish (SF): Rare, task B finishes when A starts
Calculating the critical path:
1. List all tasks and their durations
2. Identify dependencies between tasks
3. Create a network diagram
4. Perform forward pass (calculate earliest start/finish)
5. Perform backward pass (calculate latest start/finish)
6. Calculate float (latest start - earliest start)
7. Tasks with zero float form the critical path
Example:
- Task A (3 days) → Task B (5 days) → Task D (2 days) = 10 days
- Task A (3 days) → Task C (2 days) → Task D (2 days) = 7 days
- Critical path: A → B → D (10 days)
- Task C has 3 days of float
Using CPM in project management:
- Focus attention on critical tasks
- Identify where delays will impact schedule
- Find opportunities for parallel work
- Determine where adding resources helps
- Make informed trade-off decisions
Limitations:
- Assumes accurate duration estimates
- Doesn't account for resource constraints
- Static - needs recalculation as project progresses
- Doesn't handle uncertainty well (use PERT for that)
CPM is most valuable for complex projects with many interdependent tasks where understanding the schedule drivers is critical.
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