Critical Path Method


Let's be honest!!! I was afraid of Critical Path Method while being a kid. Today, I decided to face my fears and help others understand with a simple example

It is often difficult to full understand & acknowledge the complexity of a Project unless you look at the Critical Path.

By the definition of it, a Critical Path is determined by identifying the longest stretch of activities in a project plan which must be completed on time for the project to complete on due date. An activity on the critical path cannot be started until its predecessor activity is complete; if it is delayed for a day, the entire project will be delayed for a day unless the activity following the delayed activity is completed a day earlier.

The critical path method (CPM), or critical path analysis (CPA), is an algorithm for scheduling a set of project activities. It is commonly used in conjunction with the program evaluation and review technique (PERT). A critical path is determined by identifying the longest stretch of dependent activities and measuring the time required to complete them from start to finish

Case Study – Jay is a fantastic Project Manager who has lesser experience and has received a new site set up project where he will launch a service desk for which his company has just received business from a new client

Jay decides to use Critical Path Method to understand the Project duration

Step 1
After initial Due Diligence, the Project Manager outlines the below High-Level Activities. The PM also writes down duration and dependent activities to start the respective activities

Critical Path Method

Step 2
To identify the Critical Path using Critical Path Method, the PM puts all of the activities on a Network Diagram:


A Network Diagram depicting sequence of activities…

Step 3

Now the PM allocates Early Start & Early Finish for each Activity. This is done in Chronological Order from Left to Right {A to G in this sample case}


Early Start & Early Finish are depicted in top row Adjacent to the Activity

Warning: This activity is also known as Forward Pass as we move from Activity 1 to last activity. While doing a forward Pass the EF is a Calculated Field

Step 4

Now the PM allocates Late Start & Late Finish for each Activity. This is done in Reverse Chronological Order from Right to Left {G to A in this sample case}. This is the reason this concept is also called Backward Pass.



Late Start & Late Finish are depicted in the row below the activity name…

Caveat: While doing a backward Pass the LS is a Calculated Field.Once you have populated the LS and LF you can identify and understand the Critical Path activities. Most individuals could get confused while doing a backward pass – for example at C Last Finish will be taken as 65 as this task has to feed task F on 65th day.

Step 5
Activities where EF = LF are the critical Path Activities.
In the above example AEFG are Critical Path Activities

In other words activities like IT Infra Set Up, Facilities set up that cannot be overlapped are often on the critical Path.

Critical Path Method is #1 in Project Management repertoire

In project management, a critical path is the sequence of project network activities which add up to the longest overall duration, regardless if that longest duration has float or not. This determines the shortest time possible to complete the project. There can be 'total float' (unused time) within the critical path..

In most industries, the Project Manager finds that Hiring, IT Infra Set Up, Contracting and Training are always on Critical Path. This helps him drive discussions with Key stakeholders and Priortize activities as per their Critical Path

A Critical Path activity may not be crashed or fast tracked. This means that neither can you add resources to shorten the expected duration not run any tasks in parallel.

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