Critical path method, step by step
The critical path is the longest chain of dependent tasks. It sets the shortest possible project duration.
The steps
- List tasks and durations. Ideally from a WBS.
- Add dependencies. Which tasks must finish (or start) before others.
- Forward pass. For each task, early start is the latest early finish of its predecessors; early finish is early start plus duration.
- Backward pass. From the project end, work back to find the latest start and finish each task can have without moving the end.
- Calculate float. Float (slack) is late start minus early start.
- Critical path: the tasks with zero float.
Example
If Wireframes (5 days) must finish before Visual design (6 days), which must finish before Frontend (12 days), then Testing (5 days), the chain is 28 working days. A Backend task of 10 days that runs alongside has 18 days of slack, so it is not critical.
Using it
- Protect critical tasks; slips there move the end date.
- To shorten the project, shorten critical tasks or overlap them with start-to-start links.
- Re-check after every change, because the path can switch to another chain.
GenuinePlan does the calculation for you: critical path software.
Frequently asked questions
Can there be more than one critical path?
Yes, if several chains have the same total length.
What is float?
The time a task can slip without delaying the project. Critical tasks have none.
Related
Critical path
The critical path is the chain of tasks that decides when the project ends. GenuinePlan calculates it for you and highlights it on the chart.
Read more →Dependency types
A dependency says how one task's timing relates to another's. There are four types, and lag or lead fine-tunes them.
Read more →Project baseline
A baseline is a snapshot of the approved plan. Without it, you can see that dates moved but not by how much.
Read more →Plan your first project in a few minutes.
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