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Critical Path Method in Project Management

What Is the Critical Path Method (CPM)?

The critical path method in project management is the longest possible sequence of activities. It must be completed in order to successfully deliver a project from start to end. The activities on the critical path method are typically known as Critical Activities. In other words, if they get delayed, the whole project gets delayed effectively, and therefore, by finding the critical path you can the actual duration of a project. You will have a better picture of the Project’s total schedule. Traditionally before the advancement of Project Management Software project managers used to draw the critical path method network diagram by hand over the chart. However, today Critical Path can be calculated automatically with project scheduling software. It is much easier and faster.

In this article, we will analyze and understand the critical path method in PMP Certification Training Course. It will figure out associated terms along with it.

Critical Path Method Network Diagram

In a project, the Critical Path Method network diagram is a tool. It shows the order in which Project activities are scheduled. It is conducted to achieve the goal of the Project. The Project network diagram is a representation of the Project Schedule and is done in a graphical manner. So, In the PMBOK guide, this diagram is called as Project Schedule Network Diagram. This diagram is a combination of boxes and arrows, it is usually drawn from the left to right sequence. Here boxes are referred to as Activity Nodes. Hence, the reason why it is called Activity On Node or AON diagram.

critical path network diagram
critical path network diagram

The Project Schedule Network Diagram completes for the Project. You will end up having begun and end dates of each activity that occurs from the start of the project to the end. Various Project Activities will be sequenced and completed in order. It is based on the relationship between those activities. The critical path method is used to find the longest path for sequenced jobs. This is because it gives the actual project duration.

Now, in this article, we will explore the critical path method in the project management course. It will emphasize how it is calculated? Also, the other factors that hover around the Critical Path Method.

How to Find the Critical Path?

The critical path of a project is calculated by first identifying all possible paths of activities from the start of the Project in the network diagram to the end of the Project. Once all possible paths of activities are determined, the longest path in the project goes from the start until the end. it will be the Critical Path. We can consider the closest or nearest path to the identified Critical Path. Considering in terms of Project duration is the Near Critical Path. Consider that your project’s critical path is 14 months. And if the nearest path that is close to 14 months in the Project network diagram is 12 months. the Near Critical Path will be 12 months.

Critical Path Method Example with Solution

Now let us take an example. We will consider a set of activities. We can determine the Critical Path Method. It is for the Network Diagram. Since it will be based on those activities.

critical path method example with solution
critical path method example with solution

From the above table of Activities, we can see each activity with its duration in days. Since it also has the dependency of each activity on other activities. The next logical step is, using these relationships in order to draw the project network diagram. It comes right as below. You can also verify this against the diagram, for instance, keep in mind that this is the most basic version of the network diagram. It does not include other activity attributes since some of them like an early start, early finish, late start, late finish, etc.

CPM network diagram
CPM network diagram

Once you are done with the network diagram you will see that the diagram also has all activity paths from the start until the end of the project and will be relevant in order to complete the project. We will go over these paths one by one now in order to identify the critical path of the project.

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Possible Paths

So, what are the possible Paths from Start to End? It is in the given diagram?

The Path #1: ABDGH = 3+4+5+4+3 = 19 Days

network diagram
network diagram

The Path #2: ACEGH = 3+2+1+4+3 = 13 Days

network diagram1
network diagram1

Path #3: ACFH = 3+2+2+3 = 10 Days

Critical Path of this network diagram
Critical Path of this network diagram

In other words, It is clear here that out of the three possible paths the longest path is Path #1 ABDGH = 19 Days. Therefore, Path #1 is the Critical Path of this network diagram. This means this is also the Project Duration (19 Days).

Associated Terminologies

Now that we have an understanding of what is a Critical Path Method. Let us try to understand more advanced factors involved in the process.

Start and Finish

The float is also known as Slack. It is the amount of duration an activity can be delayed without causing any delays. So, It can be on the Project level. It can also be done in any of the other succeeding activities. We try to understand different types of Floats. let’s understand some additional concepts.

  • Earliest Start (ES): It the earliest possible time that an activity can be started in the project.
  • Latest Start (LS): It the latest possible time that an activity can be started in the project.
  • Earliest Finish (EF): It the earliest possible time that an activity can be finished in the project.
  • Latest Finish (LF): It the latest possible time that an activity can be finished in the project.

These attributes are denoted in an activity node like below

network diagram2
network diagram2


Forward Pass

An Early Start and Early Finish are calculated. it is done using Forward Pass, and the formula is:
Early Finish = Early Start + Duration of the Activity.
Early Start = Largest Early Finish of Preceding activities.
NOTE: the first node of the sequence has an Early Start value of “Zero.”
Below is an example diagram. it shows how a Forward Pass has been used to calculate Early Start and Early Finish

Forward Pass
Forward Pass
Backward Pass

Late Start and Late Finish are calculated using Backward Pass, and the formula is:
A Late Start= Late Finish – Duration of the Activity
Late Finish = Smallest Late Start of Succeeding activities
NOTE: The last node of the sequence has a Late Finish value of “Project Duration.”
Below is an example diagram. it shows how a Backward Pass has been used. it is done to calculate Late Start and Late Finish

Backward Pass
Backward Pass


There are two major types of Floats.

Total Float

The duration of an activity can also be delayed by the team. it is done without delaying the Project’s end date. It is called the Total Float. in other words, You would have guessed by now that Critical Path Activities. As a result, This will have a float of Zero. It is also the longest possible path in the project.
The formula for Total Float: Total Float = Late Finish – Early Finish (Or Late Start – Early Start)
Using the formula. Hence, Total float on every activity, for our example, is calculated in Green Circles.

Free Float1
Free Float

Free Float

For instance, The duration of time an Activity can be delayed by the team. since It is done without delaying the Early Start of a Succeeding Activity is called Free float. Like Total Float, all activities in a Critical Path will also have a float of Zero. it is for the same reasons explained above.
The formula for Free Float:
Free Float = Min (ES of Successors) – ES of Activity – Duration of Activity
Using the formula. Hence, Free float on every activity, for our example, is calculated in Blue Circles.

Free Float1
Free Float1


Keep in mind that a Project can have more than one Critical Path. For instance, Several Critical Paths mean that the project has high risk. Also, the Critical Path of the project can change over a period of time. Hence, always track the actuals alongside the baseline project plan. And keep monitoring the up-to-date Critical Path in order to ensure the success of the Project.

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