Project management is just as key to the success of a product as a unique idea or powerful technology. That is why project management is advancing, providing its techniques and tools to make development more flexible, higher quality, and more profitable.

In this article, we will explore the Critical Path Method (CPM) approach concept in detail, including its benefits, limitations, and key considerations for implementation. By the end, you will understand how the CPM can streamline project management, reduce costs, and improve overall project outcomes.

What is the critical path method?

The Critical Path Method (CPM) is a project management technique that provides a structured framework for planning, scheduling, and managing complex projects with many dependencies between the tasks. By identifying the critical path, which represents the sequence of tasks that must be done on time for the project to be completed on schedule, project managers can prioritize their efforts and ensure timely completion.

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Importance of the critical path method

The CPM has played a crucial role in developing project management as a discipline. It first emerged in the late 1950s as part of the larger Program Evaluation and Review Technique (PERT), which was developed to help manage time-sensitive projects of the U.S. Navy. It is mostly used for managing large projects with floating task deadlines and considering unexpected factors.

This technique then spawned others to help deal with different projects, and CPM became one such successor. It has become widespread in a number of other industries where missing deadlines or not doing tasks in the right order can have serious safety and cost implications.

For example, in the construction industry, CPM is essential for managing the many interdependent tasks involved in building projects, such as site preparation, excavation, foundation work, and superstructure construction. In the healthcare industry, CPM manages the many complex tasks involved in developing new drugs, from early-stage research to clinical trials and regulatory approval. In mechanical engineering, CPM helps engineers manage the design, testing, and production of engine components, from the design of individual parts to the final assembly of the engine. 

Critical path method benefits

However, CPM is also not perfect, and while some projects can get a huge number of benefits, others have certain limitations. Let's understand them in detail. 

  • Precise planning
    CPM enables project managers to identify the critical path of a project and prioritize the most important tasks. This leads to a more realistic project schedule, allowing the teams to allocate resources more efficiently and ultimately deliver the project on time and within budget.
  • Visualize project dynamics
    CPM provides a clear visual representation of a project and its dependencies, allowing project team members, stakeholders, and customers to better understand the project. This helps improve communication, decision-making, and early identification of potential issues or delays.
  • Early detection of potential delays
    CPM helps identify potential delays early on in the project, allowing project managers to take corrective action before the issue becomes critical. This improves the chances of completing the project on time and within budget.
  • Resource optimization
    CPM helps in optimizing resource usage by determining which tasks are critical and which can be deferred. This ensures that the project is completed with the optimal utilization of resources, reducing the chances of overallocation or underutilization.
  • Improved risk management
    CPM helps in identifying risks and uncertainties that may affect project duration. Using this information, project managers can develop risk mitigation strategies and contingency plans, ensuring that the project is completed on time and within budget. This leads to increased stakeholder satisfaction and can ultimately result in future project opportunities.

Critical path method limitations

While CPM is a widely-used and effective project management technique, it is not without its drawbacks. Here are some potential limitations of using CPM:

  • CPM is complex
    Implementing CPM can be complex, especially for larger projects with many activities and dependencies. It requires a lot of planning and coordination to ensure that all the activities are properly identified and linked.
  • CPM can be time-consuming
    Identifying all the activities and their dependencies can be time-consuming and may require significant resources to complete the project on time.
  • CPM assumes all activities are known
    CPM assumes that all the activities and their durations are known with certainty, which may not always be the case in real-world projects. Uncertainty in activity durations or unexpected events can affect the accuracy of CPM-based schedules.
  • CPM is rigid
    Once the critical path is identified, it becomes difficult to change the project plan without affecting the overall schedule. This rigidity can make adjusting to changes in project scope, timelines, or resources difficult.
  • CPM does not account for resource constraints
    CPM assumes that all resources are available to complete the project activities, but in reality, resource availability may be limited. This can lead to delays or overburdening of resources, which can affect the project schedule.
  • CPM may not account for non-critical tasks
    CPM prioritizes critical tasks and does not account for non-critical tasks that may still impact the project's success. Neglecting non-critical tasks may lead to issues with quality, stakeholder management, or other important aspects of the project.

Overall, while CPM can be an effective project management technique, it is important to be aware of its limitations and potential drawbacks when deciding whether to use it for a particular project.

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How to use the critical path method?

Before going on, it needs to understand whether CPM suits your project. CPM is a statistical method that uses a deterministic model to plan and control well-defined actions and is used to identify the critical path, which is the sequence of tasks that must be completed on time to ensure the project is completed by the target completion date.

How to Use the Critical Path Method?

However, in some cases, the deterministic approach CPM uses may not accurately represent the project timeline for projects that involve a large degree of uncertainty. For such cases, PERT suits better because it uses a probabilistic model to plan and control uncertain actions. 

But PERT cannot be fully compatible with CPM and requires a separate discussion, so we will not focus on it here but instead dive into CPM. No worries, other ways to omit CPM limitations we will discuss later. However, there is one technique that CPM not only works well with but even profoundly needs and that you should know about in advance.

The Work Breakdown Structure (WBS) is a crucial aspect of CPM that enables project managers to break down a project into smaller, manageable parts. The WBS provides a clear and organized overview of the project's scope, ensuring no critical tasks are missed. This helps to identify and define all the tasks and work items required to complete the project successfully.

What elements does CPM include?

In addition to the WBS, there are a few other key concepts of CPM itself that you should familiarize yourself with before you try it. 

  • The project activity list
    The project activity list is a comprehensive list of all the tasks and work items required to complete the project. The project activity list is used to create the WBS and is the foundation for the project network diagram.
  • The project network diagram
    The project network diagram is a graphical representation of the project schedule that shows the interdependencies between tasks. It calculates the critical path and determines the float/slack for each task.
  • Project duration
    Project duration is the time required to complete a project. Project duration is a critical factor in CPM as it directly impacts the budget and overall success.
  • Resource constraints on the project schedule
    Resource constraints, such as limited availability of personnel, equipment, or materials, can impact the duration of tasks and ultimately affect the overall project timeline.
  • Early start and early finish
    Early Start and Early Finish are a task's earliest possible start and finish times based on the project schedule and the interdependencies between tasks. Early Start and Early Finish provide project managers with a baseline for the project schedule and are used to determine the critical path.
  • Late start and late finish
    Late Start and Late Finish are a task's latest possible start and finish times based on the project schedule and the interdependencies between tasks. Late Start and Late Finish provide project managers with an understanding of the flexibility in the project schedule and are used to determine float/slack.
  • Float/slack
    Float/Slack refers to the time a task can be delayed without affecting the overall project timeline. It is the difference between a task's Late Start and Early Start or a task's Late Finish and Early Finish. Understanding Float/Slack is important in CPM as it gives project managers a buffer to allow for unexpected events or changes to the project schedule.

How to calculate critical path?

How to Calculate Critical Path?
  • List all tasks and estimate their duration
    Break down the project into smaller, more manageable components using a WBS. Estimate the duration of each task in the list using expert judgment, historical data, or a combination of both.
  • Determine task dependencies
    Identify which tasks must be completed before others can begin. Represent the dependencies using arrows, with the tail pointing to the task that must be completed first and the head pointing to the dependent task.
  • Create the project network diagram
    Arrange tasks and their dependencies in a graphical format using a network diagramming tool like Microsoft Project or a flowcharting tool like Visio. The network diagram shows the interdependencies between tasks and the critical path.
  • Calculate the earliest start and finish times
    Calculate the earliest start time (ES) and earliest finish time (EF) for each task by using the formula ES = Max (EF of preceding task) and EF = ES + duration of the task.
  • Calculate the latest start and finish times
    Calculate the latest start time (LS) and latest finish time (LF) for each task by using the formula LF = Min (LS of subsequent task) and LS = LF - duration of the task.
  • Identify critical path tasks
    Tasks with zero total slack (TS = LS - ES) are on the critical path. The critical path is the longest sequence of tasks that must be completed in order to complete the project on time.
  • Update the project network diagram
    Use the critical path information to update the project network diagram, which is used to monitor the progress of the project and make any necessary adjustments to the schedule.
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How to work with parallel tasks in CPM?

As we said before, CPM works great with the exact calculation of when tasks begin and end, considering their dependencies and ensuring a strict and necessary order of execution. But what if the tasks in your project don't go one by one, and you need to do some of them in parallel? As promised, we will recommend changing the standard CPM approach and getting around this limitation. To build a CPM with tasks that have dependencies but can work in parallel and be integrated at the end, you can follow these steps:

  1. Identify all the tasks required to complete the project and their dependencies using WBS.

  2. Determine the duration of each task and whether they can be performed in parallel. Parallel tasks can be shown as separate paths on the network diagram.

  3. Create a network diagram that shows all the tasks and their dependencies. The diagram shows parallel tasks as separate paths that merge back together once the parallel activities are complete.

  4. Determine the earliest start and finish times for each task by working forward from the project start date, taking into account the duration of each task and its dependencies.

  5. Determine each task's latest start and finish times by working backward from the project end date, considering the critical path.

  6. Identify the critical path, which is the sequence of tasks with the longest total duration. Any delay in completing a task on the critical path will delay the entire project.

  7. Monitor the progress of the critical path tasks and take action to keep them on schedule.

  8. Once the parallel tasks are complete, integrate them back into the main critical path.

It is important to note that when creating a CPM with parallel tasks, properly identifying the dependencies between the tasks and their durations is exceptionally crucial. This will allow you to accurately determine the critical path and allocate resources efficiently to keep the project on schedule.

Example of critical path in project management

Let's now look at the example of making a Web site. Yes, the example is extremely simplified because making even the simplest website involves much more tasks. But here, it is important to understand how CPM helps organize management. 

And if you are interested to learn more about how to develop any software step by step, read our book Software Development Approaches, in which we share the best development practices that we have collected, implemented, and improved for many years.

List all tasks and estimate their duration

  • Gather Requirements (2 days)
  • Create Design Mockup (3 days)
  • Develop HTML Markup (4 days)
  • Develop CSS Styles (4 days)
  • Develop JavaScript Functionality (5 days)
  • Test and Debug (3 days)
  • Set up server infrastructure (2 days)
  • Develop server-side code (6 days)
  • Integrate front-end and back-end (3 days)
  • Test server-side functionality (3 days)
  • Deploy the website to a server (1 day)

Determine task dependencies

  • Gather Requirements has no dependencies
  • Creating Design Mockup depends on Gather Requirements
  • Developing HTML Markup depends on Create Design Mockup
  • Developing CSS Styles depends on Create Design Mockup
  • Developing JavaScript Functionality depends on Developing HTML Markup and Developing CSS Styles
  • Test and Debug depend on Develop JavaScript Functionality
  • Integrate front-end and back-end depends on Developing server-side code and Developing JavaScript Functionality
  • Test server-side functionality depends on Integrate front-end and back-end
  • Deploy the website to the server depends on Test server-side functionality

Create the project network diagram

Create the Project Network Diagram

Calculate the earliest start and finish times

Tasks Earliest Start (days) Finish Times (days)
Gather Requirements 0 2
Create Design Mockup 2 5
Develop HTML Markup 5 9
Develop CSS Styles 5 9
Develop JavaScript Functionality 9 14
Test and Debug 14 17
Set up Server Infrastructure 17 19
Develop Server-Side Code 19 25
Integrate Frontend and Backend 14 17
Test Server-Side Functionality 17 20
Deploy the Website to the Server 20 21

Calculate the latest start and finish times

Tasks Latest Finish (days) Latest Start (days)
Develop Server-Side Code 26 20
Set up Server Infrastructure 21 17
Test and Debug 20 17
Develop JavaScript Functionality 19 14
Develop CSS Styles 13 9
Develop HTML Markup 13 5
Create Design Mockup 4 2
Gather Requirements 2 0

Calculate the total slack

  • Gather Requirements:
    TS = LF - EF = 0
  • Create Design Mockup:
    TS = LF - EF = 0
  • Develop HTML Markup:
    TS = LF - EF = 0
  • Develop CSS Styles:
    TS = LF - EF = 0
  • Develop JavaScript Functionality:
    TS = LF - EF = 0
  • Test and Debug:
    TS = LF - EF = 0
  • Set up Server Infrastructure:
    TS = LF - EF = 0
  • Develop Server-Side Code:
    TS = LF - EF = 1
  • Integrate Frontend and Backend:
    TS = LF - EF = 0
  • Test Server-Side Functionality:
    TS = LF - EF = 0
  • Deploy the Website to the Server:
    TS = LF - EF = 0

Identify critical path tasks

The critical path for this project includes tasks 1, 2, 3, 4, 5, 6, 7, 10, and 11, which have zero total slack.

Update the project network diagram

Update the Project Network Diagram

Now you have a diagram including all the tasks and reflecting their dependencies, as well as the obvious critical path that needs special attention in development. Such a calculation and its visual representation will greatly help manage the project in the most obvious way, avoiding downtime and broken deadlines.

Summary

Now you know what CPM is and why it is so important. CPM helps software development professionals to manage projects more effectively by breaking down the project into smaller, more manageable components and focusing on the critical path. By using CPM, you can anticipate potential delays, make informed decisions about resource allocation, budgeting, and scheduling, and keep your project on track.

Also, you now know exactly when and how to use it. CPM can be applied to all phases of software development, including planning, design, development, testing, and deployment. Identifying task dependencies and parallel activities can shorten the project's duration and improve overall efficiency. 

And if you still have questions, ask for our free consultation. Our experts will carefully review your project and select the most suitable techniques and tools for its management, ensuring the highest quality and benefit from the final product.

FAQ

What is the Critical Path Method (CPM), and why is it important in software development?

What are the benefits of using the Critical Path Method in software development?

What are the limitations of using the Critical Path Method in software development?

When should you use the Critical Path Method in software development?

Why must non-critical tasks be monitored in software development?

Can CPM be used in Agile software development?

Can CPM be used for small software development projects?

Can the Critical Path Method be automated in software development?

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