Critical Path in Project Management

The critical path in project management refers to the order of work that needs to be completed to guarantee the project is on schedule. It is the longest path in the project, and any delay on the critical path would cause the project’s completion date to be pushed back.

Critical Path Method in Project Management
The critical path is the longest sequence of tasks in a project that must be completed in order to meet the project's deadline.

Elements of the Critical Path:

  • Tasks/Activities:  These are individual tasks that you must accomplish within a project.
  • Duration: The time it takes to complete a task. This can be in days, weeks, or any other time unit.
  • Dependencies:  Connections among tasks that dictate the sequence of their completion. Tasks can be dependent on one another or independent.
  • Early Start (ES) and Early Finish (EF): The earliest possible start and finish times for a task, considering dependencies and the project’s start date.
  • Late Start (LS) and Late Finish (LF): The latest possible start and finish times for a task without delaying the project’s completion date.
  • Float/Slack: The time span a task can be postponed without impacting the overall duration of the project. Tasks on the critical path have zero float.

Identifying the Critical Path:

To determine the critical path, follow these steps:

  • Create a Network Diagram:

    First, list all the tasks and their dependencies in a diagram. You can do this using tools like the Precedence Diagramming Method (PDM) or the Program Evaluation and Review Technique (PERT).

  • Calculate Early Start and Early Finish:

    Next, start with the project’s start date. Then, calculate the earliest start and finish times for each task, considering dependencies.

  • Calculate Late Start and Late Finish:

    Next, start with the project’s end date. Then, calculate the latest start and finish times for each task, working backward.

  • Calculate Float:

    For each task, subtract its Early Start from its Late Start to find the float. Tasks with zero float are on the critical path.

  • Identify the Longest Path:

    The sequence of tasks with the longest total duration is the critical path.

Importance of the Critical Path:

  • Time Management: The critical path helps you prioritize tasks that directly impact the project’s duration.

  • Risk Management: If any task on the critical path is delayed, the project’s completion date is at risk.

  • Resource Allocation: Resources can be allocated more efficiently by focusing on critical tasks.

  • Project Monitoring: Tracking the progress of critical tasks helps identify potential delays early on.

  • Scenario Analysis: You can analyze the impact of delaying or speeding up tasks on the critical path to make informed decisions.

Example: Project Scenario: Building a Garden Shed:

Imagine you’re tasked with building a garden shed. The project involves several tasks, each with its own duration and dependencies. Here’s a list of tasks and their details:

  1. Design Shed (A): 3 days (Start)
  2. Gather Materials (B): 5 days (Start)
  3. Lay Foundation (C): 2 days (A)
  4. Build Walls (D): 4 days (B)
  5. Roofing (E): 3 days (C, D)
  6. Paint Shed (F): 2 days (D)
  7. Install Door (G): 1 day (E)
  8. Final Touches (H): 2 days (F, G)

Tasks C and D depend on Task A. Task E depends on Tasks C and D. Task F depends on Task D, and Task G depends on Task E. Task H depends on tasks F and G.

Network Diagram:

Calculating Early Start (ES), Early Finish (EF), Late Start (LS), Late Finish (LF), and Float:

  1. Design Shed (A): ES = 0, EF = 3, LS = 0, LF = 3, Float = 0
  2. Gather Materials (B): ES = 0, EF = 5, LS = 0, LF = 5, Float = 0
  3. Lay Foundation (C): ES = 3, EF = 5, LS = 5, LF = 7, Float = 2
  4. Build Walls (D): ES = 5, EF = 9, LS = 5, LF = 9, Float = 0
  5. Roofing (E): ES = 7, EF = 10, LS = 9, LF = 12, Float = 2
  6. Paint Shed (F): ES = 9, EF = 11, LS = 9, LF = 11, Float = 0
  7. Install Door (G): ES = 10, EF = 11, LS = 12, LF = 13, Float = 2
  8. Final Touches (H): ES = 11, EF = 13, LS = 11, LF = 13, Float = 0

Identifying the Critical Path:

The critical path is the longest path through the network diagram. In this case, it’s A → D → E → G → H.


In this example, the critical path consists of tasks that have zero float, meaning any delay in these tasks will delay the entire project. Managing tasks on the critical path becomes essential to ensure the project is completed on time. Other tasks might have some flexibility in their timing (float), which provides some room for adjustment without affecting the project’s overall duration.

Remember, this is a simplified example, but it illustrates the basic principles of the critical path concept. In real projects, the critical path can be more complex, involving numerous tasks and dependencies.


In summary, the critical path is a fundamental concept in project management. It illustrates the sequence of tasks that establish the shortest time to complete a project. Tasks on the critical path have zero slack or float, meaning any delay in these tasks will delay the project. To find the critical path, you create a network diagram of tasks with their durations and dependencies. By calculating early start, early finish, late start, late finish, and float for each task, you identify the longest path through the diagram, which is the critical path. Overall, managing tasks on this path is crucial for meeting project deadlines and understanding the interdependencies between tasks.

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