The Critical Path Analysis In Project Management

CPA is a technique that is used to identify the tasks which must be completed on time for whole project to be completed on time. In other words, CPA is a technique used identify the minimum length of time needed in order to complete the project. Where we need to robust the projects, it helps to identify and plan which project steps should be accelerated using required number of resources to complete the project within available timeline. The CPA comes into handy while planning project activities for handling complex and urgent tasks and projects with large number of activities. CPA is a key component in reducing the project timelines and costs.

The reviewing of the overall Work Breakdown Structure (WBS) & PERT is done before moving onto the CPA. This is because when using CPA, some activities cannot start until and unless other activities are finished and in some case, must be executed in a sequence. The CPA of the WBS diagrams the time necessary to complete an activity, activity dependencies, milestones, deliverables and how each activity is connected to each other.

In general, CPA plans and organizes resources, prioritizes tasks, time estimates, minimizes project timelines and helps providing proper guidance to the project.

CPA Example:

Let us assume, we have list of activities with the dependencies, requirements and time duration as:

Fig: Tasks and Dependencies between the tasks

The step now is to define the sequence of activities that represents the longest path through the project. The operations to be performed are:

  • Calculate Forward pass (Early Start, Early Finish)
  • Calculate Backward pass (Late Start, Late Finish)
  • Calculate Float
  • EF = ES + duration — 1
  • LS = LF — duration + 1

Calculating from the Forward Pass

  • What is the earliest start date and earliest Finish date of each activities
  • For starting of the project, ES = 1
  • Calculate ES and EF for each activities
  • In the example above, completion of Task A and B will kick start Task E. Hence, even if Task A is getting over in day 5 and Task B is getting over in day 3, Task E cannot be kick started before day 6. ES for Task E= 6.
  • Same case applies for other activities as well
Fig: CPA with Early Start and Early Finish from Forward Pass

Calculating from the Backward Pass

  • Will be started from the last date and late start and late finish date of each activities
  • In an example above, the Task F will be complete on day 15. Hence, the LF = 15
  • Task E, Task C and Task D must Get over by latest on day 11, So , LF = 11 & LS for Task E, Task C and Task D is 6, 6 & 5 respectively.
  • Late Start for Task E is 6 and Task D is 5. Hence, Late finish for Task B is 4
Fig: CPA with Late Start and Late Finish from Backward Pass

Calculate Float (Slack)

  • Float = LS — ES “OR” LF — EF
  • Float (Slack) is a buffer on which if the tasks are delayed by calculated rate, will not bring changes in the project completion date.
  • If Float = 0: Critical Path
Fig: Path showing the Critical Paths in a project

Results from CPA

  • In our example, the float/slack/buffer of critical path [path marked as red] activity is 0 ; means, if we delay on any of the activities then our project will be delayed
  • The critical path to which project takes minimum amount to time to complete is 15 days. Task A -> Task E-> Task F
  • The resource allocation for the Critical path calculated activities must be done in such a way that they have minimum impact on project schedule and there must not be any delays in those activities. As, completion of these activities denotes the completion of whole project in a minimum amount of time
  • Monitoring the Critical Path must be done very carefully and activities to pay attention to.
  • Critical path activities means it is on a very high risk with respect to the schedule
  • This makes the prioritization planning very easy and makes the team easy to plan the sprints as well.