Difference Between PERT and CPM in Project Management

Project management seems like solving a puzzle with a time frame, tasks and resources.  And here comes the importance of PERT and CPM tools in project management. While planning for complex projects, many beginners inquire what is PERT and what is CPM?

To choose the right method and complete assigned tasks before the deadline, understanding the difference between PERT and CPM is crucial. While PERT focuses on uncertainty, CPM is all about control and efficiency. These two concepts help project managers in well planning and achieving success. Continue reading this blog to learn the difference between PERT and CPM.

What is PERT in Project Management?

PERT in project management means Project Evaluation and Review Technique. This is a popular technique used across all projects to determine the accurate time needed to complete different activities. This well-known planning tool also lets you calculate the adequate time required to finish a project. 

PERT is used widely for scheduling, organising and task integration in a project. Alongside providing the project blueprint, it is a great tool for project evaluation. 

Using this tool, you can also prepare a PERT chart representing a proper schedule of all specific tasks involved in a project. The PERT chart lets you schedule, organise and coordinate tasks associated with the project. 

The main objective of PERT chart is, however, to determine the critical path, comprising several critical activities to complete within a specified schedule. 

When to use PERT?

PERT is applicable when there is uncertainty in a project and little experience. PERT applies to projects which are hard to estimate. PERT application is good for projects relating to research and development. It also comes in handy during work on innovations or experimentation. PERT is applicable in the case of a new project or a first-time project. It helps managers in the planning process even when the information is not fully available. 

PERT is more useful when deadlines hold more significance than other factors, such as cost control. It allows you to gain  freedom in scheduling and time prediction. PERT is best indicated when there is interdependence. It considers the use of time estimates to make decisions under risk. PERT helps managers point out significant milestones and track the work. 

What is CPM in Project Management?

CPM in project management stands for the critical path method. It denotes a series of tasks to complete to determine how fast you can reach the desired completion time of a project. In project management, the critical path implies maximum time for completion of a project      within the shortest timespan possible. If you fail to complete any of these tasks within the desired time, your project deadline will be delayed     . 

Be it any critical or non-critical tasks, you will be assigned a fixed start date, end date and particular time. Here, the domino effect applies, which states: if there is a delay in any task within the critical path, what's the ripple effect on other tasks?

But CPM also plays a considerable role in optimising the path. Through constant evaluation and adjustment of project activity, CPM ensures the project stays on track, even if there are any unforeseen circumstances. 

When to use CPM?

CPM applies to a project comprising well-defined and clear activities. It is most effective where the task time is easily predictable. CPM is applicable in construction, manufacturing and infrastructure construction. These projects have a specified order of activities. CPM is applicable in situations when time and cost control are significant. It assists managers in balancing time of project and costs. 

CPM also outlines some key activities which are not necessary to postpone. CPM suits well with repetitive or routine projects. It is conducive to effective planning and allocation of resources. CPM is employed by managers to maximise manpower, materials and equipment. 

PERT and CPM Charts Explained with Examples

PERT and CPM charts are project management tools useful in managing and tracking work. The PERT chart is concerned with events and uncertain periods of events. The CPM chart is concentrated on activities whose time estimates are definite. 

For example, consider a software development project. Tasks relating to design, coding, testing and review do not have definite timelines in a PERT chart. Every task tends to be optimistic, most likely and pessimistic times allotted to it. 

Fixed durations are allotted to each task of the same project in a CPM chart. The critical path is pointed out in the chart. Any delay in such activities results in delaying the whole project. This illustrates the major difference between PERT and CPM in project management.

8 Major Differences Between PERT and CPM

PERT and CPM comprise key differences with distinct characteristics. Find below the major differences between PERT and CPM: 

1. Event-Oriented and Activity-Oriented

   PERT is a time event-based method. It is concerned with the activities or events which identify the beginnings and end of activities. CPM is a method that is activity-based. It is oriented on activities, and the duration of performing the activities. 

2. Unpredictable Vs. Predictable Activities

   PERT is applicable in the case of uncertain and unpredictable activities. The time estimates can fluctuate because of risk or the nonexistence of previous information. CPM is applied when there is predictability of activities. 

3. Time Control Vs. Time Cost Trade-off

   PERT is used primarily to control time. It assists managers in estimating the time of project completion in the event of uncertainty. CPM is time and cost-oriented. It enables managers to decrease the time of the project by adding the cost, also commonly known as the time-cost trade-off. 

4. One-off Vs. Repetitive Projects

   PERT is more appropriate for a one-time or non-repetitive project. Such cases are research, development or new product launches. CPM applies to repetitive projects. Examples are construction, manufacturing, and maintenance work. 

5. Milestone Vs. Tasks as Chart Nodes

   In PERT, the nodes are the milestones or events. Arrows represent these activities. The nodes are the activities or tasks in CPM. This enables CPM diagrams to be read and followed more easily. 

6. Probability Model and Deterministic Model

   PERT follows a probability model. It employs three-time estimates, i.e., optimistic, most probable, and pessimistic. CPM is detached from the deterministic model. It makes use of a single constant-time estimate of each activity. 

7. No Resource Crashing Vs. Resource Crashing

   PERT is not based on the crashing of resources. It is primarily concerned with uncertainty scheduling. CPM permits crashing of resources. Project Managers also have the option of putting additional resources into activities critical to reduce the project duration. 

8. No Critical Activities Vs. Distinguished Critical Activities

   Instead of a clear definition of critical activities, PERT lacks this. It principally determines key events. CPM can clearly identify the critical activities as well as the critical path. Any latitude in such activities will postpone the whole project. 

Advantages of Using CPM in Project Management

Here are the key advantages of using CPM in project management:

• CPM Benefits: Facilitates enhanced task scheduling

Enhanced task scheduling is one of the CPM advantages. CPM splits the project into certain activities and organises them in a structured order. This helps the managers to strategise the work. The critical path is also clearly defined. That is one of the key differences between PERT and CPM project management.

• CPM Benefits: Measures project progress efficiently

Managers can easily monitor the tasks completed and also those awaiting performance. You can easily identify a delay in the project. This helps in improved deadlines      and cost control. In the comparison between PERT and CPM, CPM is better for predictable projects.

What are the Advantages of Using PERT in Project Management?

The key advantages of using PERT in project management are: 

1. Flexibility 

   PERT is very versatile in nature. It changes the required schedule in case there is a variation in the project. This also helps in the easy application of new projects. Managers can thus revise time estimates without interrupting the whole course of action. This is useful in the dynamism of the project environment.

2. Risk Awareness

   Risk awareness is just one of the big benefits of PERT in project management. It applies three time estimates on the activities. These are prosperous, probable, and unfavourable periods. This method identifies the potential delays and uncertainties. Backup plans can be made beforehand by the managers.

3. Clear Visualisation of Project

   PERT offers a clear visual presentation of the project. The network diagram demonstrates the flow of activities and events. This assists the teams in knowing the general flow of a project. It enhances transparency to managers and stakeholders. 

4. Activity Analysis

   PERT facilitates fine analysis of the activities. Every activity is sub-dissected and researched. Managers are capable of viewing the task dependencies and relationships. This assists in discovering problem areas in time. It enhances planning and prioritisation of tasks. 

5. Coordination Ability

   PERT enhances higher coordination among various teams and departments. Every individual is capable of understanding their definite roles and timeline. This is particularly applicable to big projects and cross-functional projects. 

6. What-If Analysis

   PERT has the capability of what-if analysis. Managers can change the time estimation of projects for testing various realities. This thereby helps to know how delays can impact the completion of a project. It helps in making decisions during uncertain times. It is important when the deadline is paramount.

What are the Disadvantages of PERT and CPM?

Look below into the disadvantages of PERT and CPM in project management: 

Disadvantages of PERT 

1. Uncertain Time Estimation 

   PERT relies on time estimates, focusing on probability. These estimations can be inappropriate and result in creating a significant impact on the general project planning. 

2. Complicated and Time Consuming 

   PERT charts may become elaborate when it comes to large projects. They need time and effort to be created and updated. 

3. Focus on No Cost 

   PERT mainly focuses on time. It fails to address the cost control factor. Here lies the main difference between PERT and CPM. 

4. Complicated to Understand 

   PERT charts are not readily interpretable. Non-technical team members may find them difficult to understand. 

Disadvantages of CPM 

1. Need Updated and Accurate Data 

   CPM involves the use of fixed time estimations. If the data is not accurate, planning becomes unreliable and this affects project accuracy. 

2. Less Flexibility 

   CPM cannot easily adapt to frequent changes. Any change may require revising the entire project schedule. 

3. Focus on Critical Path 

   CPM focuses mainly on critical activities. Delays in non-critical activities may sometimes be overlooked. 

4. Unsuitable for Non-predictable Projects 

   CPM applies to steady projects. That is one of the major differences between PERT and CPM in project management.

How can Project Managers Use PERT and CPM Together in Project Planning?

PERT and CPM are helpful in project management to assist project managers in planning and controlling projects. PERT is used at the initial stage of planning. It is applicable in cases where the duration of activities is a cause of uncertainty. Managers are able to estimate potential schedules and find significant risks. 

On the other hand, CPM helps in setting specific timeframes and expenses for the activities. It determines the critical path and the most important activities that cannot be delayed further. Combining PERT and CPM enhances decision-making. Managers are flexible, get a better schedule and have more powerful control over the time and the cost.

How to make a PERT Chart?

Worried about meeting deadlines in your project?

Take the help of a PERT chart and stay ahead of your project deadline. Here is a detailed step-by-step guide to follow to learn how to make a PERT chart and meet deadlines with ease:

Step 1: Review Project Tasks

The first and foremost step to follow for creating a PERT chart is project planning. In this stage, you need to define the tasks to predict the approximate deadline. However, before mapping out tasks, take adequate time for collecting relevant details that include:

• A communication plan

• A business case

• An initial meeting timeline

Preparing this framework lets you stay connected with task completion and develop a clear scope before proceeding further. 

Step 2: Explain Task Dependencies

A task dependency implies a particular task to complete that depends on another task. Dependent tasks are a significant part of the PERT method, also commonly known as the logical relationship. This is often used in a work breakdown structure. 

A proper understanding of task dependencies lets you track work, ensure on-time completion of tasks and also develops clear communication – works well for complicated projects. Without any well-defined dependency, it’s challenging to prepare a timeline structure and estimate the overall duration of the project. 

A PERT diagram portrays dependencies through the well-connected tasks. This is, though not a detailed overview of breakdown structure, but reflects a transparent overview of required tasks and the relationship between tasks. 

Step 3: Establish Connection across Project Tasks

Once you complete task dependency, begin working on your PERT chart through well establishment of project tasks with one another. These connections are established through arrows and nodes. Arrows denote tasks while nodes reflect events and milestones. 

For instance, locate the main events within your nodes (reflected as squares and numbered circles) and then proceed to draw task arrows to denote the dependencies required for event completion. This kind of network diagram will be structured and simple to understand for respective project stakeholders. 

Step 4: Estimate Time Frame of Project

Now, it's your turn to determine the time you need to complete the project using the PERT equation and the critical path method. The critical path is a lengthy process to follow for task completion and to finish the project on time. 

The main goal is to locate the sequence of tasks for the accurate estimation of a short-duration project. The time estimation in PERT analysis is dependent on:

• Optimistic Time: This is the minimum time frame required to complete a task. 

• Pessimistic Time: This denotes the maximum time you need to complete a task. 

• Most Likely Time: This provides the best estimation of the length a task can take. 

Using the PERT formula, it is possible to estimate task duration and time of completion:

Expected Time = (O + (4*M) + P)/6

This can be calculated in hours, minutes, days and even weeks. 

For example, if a task requires an optimistic time frame of 15 minutes, a pessimistic time of 50 minutes and most likely a time of 45 minutes, the calculation will turn out as:

(15min + (4*45min) + 50 min)/6 = 40.8

Once you complete the PERT estimation for each task, sum them up along the critical path to derive the desired project timeline. 

Step 5: Manage the progress of the task

This is the last and final step to follow towards creating a PERT chart. Managing the task’s progress task's progress      is crucial until the completion of the project of the project     . This includes well tracking of task dependency, meeting challenges and ensuring to meet the project milestone. 

Make sure to update the PERT chart in project management whenever there are any changes. Moreover, combining it with the required change control process helps in tracking and maintaining transparent communication. 

Once you complete all these tasks, arrange all project materials in a single place for easy access to PERT analysis. 

Overall, PERT and CPM play a crucial role towards project management. Both these methods with proper use helps in enhanced planning, scheduling and monitoring. The difference between PERT and CPM reflects that no single method exists and is found to be perfect to meet all project requirements. Through well understanding of the differences between the two, managers can choose the right tool and meet project deadlines on time. 

FAQs on the Difference Between PERT and CPM in Project Management

1. Is PERT deterministic or probabilistic?

   PERT is probabilistic in nature. It is used when activity durations are uncertain and helps project managers handle risks and uncertainty during project planning.

2. Is CPM used for time or cost control?

   CPM is used for both time and cost control. It helps identify the critical path, manage project deadlines, and supports time–cost trade-off decisions during project planning.

3. What are the applications of PERT and CPM?

   PERT is commonly used in research, development, and innovation projects where activity durations are uncertain. CPM is widely used in construction, manufacturing, and routine projects with predictable task durations. Both techniques are used for project planning, scheduling, and control.

4. What is the formula for PERT expected time estimation?

   The PERT expected time formula is: Expected Time (TE) = (Optimistic Time + 4 × Most Likely Time + Pessimistic Time) / 6. This formula provides a weighted average to estimate the most realistic activity duration.

5. Why is PERT preferred for research and development projects?

   PERT is preferred for research and development projects because task durations are often uncertain. Its probabilistic approach allows flexible planning and risk analysis, making it suitable for experimental and innovative work.

6. What are the main limitations of CPM?

   CPM requires accurate and fixed time estimates for activities. It is less flexible when project conditions change and may not work well for highly uncertain projects. Focusing only on the critical path may also overlook delays in non-critical tasks.

7. How do I identify the critical path in a project network?

   The critical path is identified as the longest sequence of activities in the project network. Activities on this path have zero slack, meaning any delay in these tasks will delay the entire project.

8. Why is PERT preferred for research and development projects?

   PERT is well suited for research and development projects because it accounts for high uncertainty in activity durations. By using probabilistic time estimates, it helps managers plan projects even when complete information is not available.