What is the Critical Path Method?

The critical path is the longest succession of tasks that has to be successfully completed to conclude a project entirely. The tasks involved in the sequence are called critical activities, as any task getting delayed will result in the whole project getting delayed. To determine the time duration of a project, the critical path has to be identified. The critical path method or CPM is used by project managers to evaluate the least amount of time required to finish each task with the least amount of delay. 

Using Critical Path Method (CPM) in a project

The critical path method or CPM is an algorithm used to utilize the resources for scheduling a sequence of project tasks. First, a model is created which includes –  

  • A list of all tasks from start to finish required to complete the project 
  • The dependency of one task on another 
  • The estimated time duration  

This information helps the project manager to determine the longest path or the critical path of sequential activities to measure the duration of the project from the beginning to the end. Critical path will have the longest time duration. Any activity getting delayed on the critical path will delay the completion of the project by the same amount of time. To establish the critical path, the estimated time duration of each activity is added to the previous activity, and the path with the longest duration is determined. As shown in the network diagram below, the critical path with the sequence of tasks takes at least eight days. The duration is marked in days, and the sequential activities are shaded.  

"What is Critical Path Method"

Early Start Dates 

As demonstrated in the network diagram, proceeding from left to right, starting dates can be allotted to each activity, beginning at the project start date. This method helps derive the early start dates or ES dates. The early start date is the earliest date an activity can commence. To compute early start dates, a start date has to be assigned to acting as though there are no predecessor activities. To calculate the early start dates of the sequence of activities till the project finish time –  

  • Add the previous activity’s time duration to the starting date 
  • Add or subtract the lag or the lead time as the need be 
  • Post referring to the resource calendar concerning manpower and equipment required for the activity, the number of off-days from those activities will be added to the derived date 
  • This data derived is assigned as the early start date for the succeeding activity 

What is a Gantt Chart?

A Gantt chart or Gantt diagram is a tool in project management that maps the sequence of activities as per timelines. These activities are displayed as the bar and hence also known as bar plans or bar diagrams. A Gantt diagram helps to control activities and also evaluate the effect of delays on the project. The Gantt chart is structured around the work breakdown. This project management tool helps give a quick overview of the activities involved in the project. It also helps understand the relationship between and the dependency of the activities on each other. A Gantt chart makes it easy to identify the critical and the noncritical activities and calculate the buffer time accordingly.  

Gantt charts demonstrate project schedules by mapping the activities against the time duration. Activities are listed on the Y-axis and the time durations on the X-axis. The horizontal bars indicate the start of the activity and its duration. Gantt chart is used for the purpose of scheduling and planning and is a tool extensively used in industries like manufacturing, engineering, construction, IT, etc. Below is a sample of a Gantt chart illustrating the project schedule and the time durations. 

"What is a Gantt Chart"
CC-BY-SA 4.0 | Image Credits: https://commons.wikimedia.org/

(2021 GrapeCity) 

How to Calculate the Critical Path? 

The steps to calculate the critical path is as follows –  

-         Using a work breakdown structure to collect all activities required to finish the project 

-         Analyzing which tasks are interdependent 

-         Creating a critical path analysis or a network diagram to assign the order of activities 

-         Estimating the time duration of each activity 

-         Using a critical path algorithm to separate the forward pass and the backward pass 

-         Forward Pass uses a network diagram and the time duration of each activity to determine the early start (ES) dates and the early finish (EF) dates, where the – EF date of the previous activity identifies the amount of time expected to finish the project in its entirety. The example below identifies 28 days as the quickest the work can be finished.  

"How to calculate Critical Path"

(20|20 Business Insight Ltd) 

- Backward pass assigns the earliest finish of the previous activity as its latest finish (LF). So then, when an activity has two or more following activities, the earliest date is transferred. This process gets repeated until the LF dates are known. 

"How to calculate critical path"

(20|20 Business Insight Ltd) 

-         Next is identifying the float of each activity. Float refers to the time duration an activity can be delayed without any impact on the project completion time. There are two kinds of float –  

            Free Float – This is the amount of delay that will not affect the succeeding task.  

            Total Float – This is the amount of delay in an activity that will not affect the finish date of the project. 

Once the early start and late start for each task have been identified and the available float calculated, the critical path can be worked out. The critical path has a series of subsequent network activities with no total float. The below example shows the critical path in red. 

" How to calculate critical path "

(20|20 Business Insight Ltd) 

-         The critical path is made up of activities with zero floats. The critical path has to be identified.  

-         Finally, revising and updating the critical path network diagram during the execution process.  

The above steps determine the critical tasks and the activities that can float or can be delayed without any negative impact on the overall project duration. What should also be considered are the constraints that might affect the project schedule. These constraints have to be accounted for to increase the accuracy of the critical path method. If the constraints lead to time getting added to the project timelines, it is called a critical path drag.  

Summarizing Critical Path Method (CPM) Quiz-let 

Summarizing Critical Path Method (CPM) Quiz-let 

Early Start - The earliest an activity can start to post the logical constraints. 

Duration – The estimated time duration of the task or activity 

Early Finish – The earliest an activity can finish posting the logical constraints. 

Late Start – The latest activity can start to post logical constraints and with no impact on the overall duration of the project. 

Float – The amount of delay involved in an activity without impacting the overall duration of the project. 

Late Finish – The latest activity can end post logical constraints and with no impact on the overall duration of the project.  

Work Breakdown Structure (WBS) – A common productivity technique is to break down work into smaller tasks to make it more manageable. The project management book of knowledge or PMBOK from the project management institute (PMI) defines work breakdown structure, or WBS is a hierarchical breakdown of work for ease of the project management team. WBS can be delivery-based or phase-based.  

Theory of Constraints – developed by Dr. Eliyahu M. Goldratt, the theory of constraints or TOC is a management paradigm that observes that there are constraints that can limit the achievement of goals. TOC identifies the constraint and structures the organization around it.  

Common Mistake

It is difficult to prepare a schedule with the right amount of detail. The schedule has to be prepared to keep in mind the project management team. The most common mistake made is creating too many tasks while preparing the schedule, which will make managing work unmanageable.  

Context and Applications 

This topic is significant in the professional exams for both undergraduate and graduate courses –  

  • Bachelor of Commerce 
  • Masters of Commerce 
  • BBA 
  • MBA 
  • Strategic Operations Management 
  • Advanced Operations Management 
  • PMP Certification 


  • 20|20 Business Insight Ltd. (n.d.). What is the Critical Path? Retrieved March 27, 2021, from https://2020projectmanagement.com: https://2020projectmanagement.com/resources/project-planning/what-is-the-critical-path 
  • 2021 GrapeCity. (n.d.). Gantt Chart. Retrieved March 27, 2021, from https://www.grapecity.com: https://www.grapecity.com/componentone/docs/win/online-flexchart/gantt-chart.html 
  • The University of Minnesota. (n.d.). Critical Path and Float. Retrieved March 27, 2021, from https://open.lib.umn.edu: https://open.lib.umn.edu/projectmanagement/chapter/8-3-critical-path-and-float/ 

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