The Ultimate Manual to Critical Path Project Management

Critical path project management (CPM) is a recent addition to the growing list of project management methodologies designed to help you streamline and prioritize activities and meet deadlines. Understanding how CPM works may seem daunting, but once you understand its basics, you’re assured of having an easier time completing projects on time and within budget. Read on as we explain critical path management and its components in more detail below.

What is Critical Path Project Management Anyway?

Let’s first describe what “critical path“ means in CPM.

The critical path is the longest sequence of activities in any project plan that must be completed on time to finish the project by the predetermined deadline.

Project managers use the CPM algorithm to find this critical path, where they define the least amount of time required to complete every task with minimal slack.

In other words, critical path project management is a resource-utilization algorithm that project managers use to schedule a sequence of project-related activities.

Project Management Methodologies

The Project Management Institute defines methodology as “a system of practices, techniques, procedures, and rules used by those who work in a discipline.”

There are many project management-specific methodologies used across industries and project types around the world today. Some of the most popular project management methodologies include waterfall, agile, scrum, lean, and Kanban.

The PMI expands further in a case study stating: “Successful project management secures a company’s survival, and PMM is indispensable to ensure projects’ success.”

CPM as a methodology was created in the 1950s and can be applied to almost any industry, including software development, aerospace, construction, research, and more. It is still widely used today in various sectors to effectively manage projects of all sizes.

CPM allows project managers to visualize all aspects of the project via a timeline on a Gantt chart.

You can use project management software to help organize all tasks required to complete any project using various views and charts, including very visual Gantt charts.

How Critical Path Project Management Works

As mentioned, critical path management is essentially a decision-making algorithm that considers a task’s start time, duration, and end time to identify critical activities—ones that deserve the most attention to complete a project.

The idea behind using CPM is to construct a model of the project that includes the following aspects:

  • An activity list that covers all required tasks to complete the project
  • The dependencies between the tasks
  • Estimated duration of how long each activity may take to complete

With this information, you can identify the longest stretch of dependent activities and measure them from start to finish, which you can then use to determine the critical path. Following this, you can easily discern which tasks must be performed immediately and which can be delayed without making the project longer or going past the deadline.

Let’s take a look at how CPM helps when applied to project management plans:

  • Identifies critical tasks: CPM lets you outline the most crucial tasks to closely supervise on the critical path. If any task on the critical map takes longer than the estimated duration (i.e., starts or ends later than intended), your whole project will be affected and may get delayed.
  • Creates a shorter time frame: CPM can help shorten timelines, enabling project managers to complete projects faster. When you visualize the results from a CPM as a bar chart, you can quickly figure out where tasks fall in the overall timeline. Visualizing critical path activities, task durations, and their sequences becomes easier. You can use this information to gain a new level of insight into your project timeline, which can be used to decide task durations to modify and ones that should remain unchanged.
  • Measures actual progress against planned progress: You can use CPM to compare planned progress with actual progress to keep projects on track and get near-perfect results. As the project runs, you can work with the baseline schedule developed from the initial critical path analysis to track the scheduling process. You can also identify completed tasks, the predicted remaining duration for in-progress tasks, and any planned changes to future task sequences and durations. When displayed against the original baseline, you’ll get an updated schedule that will allow you to compare planned and actual progress visually.

Project management software is vital to completing projects on time, keeping all team members on task, and quickly identifying where a project is at any given time. Microsoft Project is a great option. The tool can clearly present all the project phases and tasks, after which it’ll automatically forecast your project’s end date.

Microsoft Project offers three cloud-based pricing plans starting at $10 per user per month. All three plans come with a centralized dashboard, multiple views, including grid, boards, and Gantt charts, and collaboration features.

You can try Microsoft Project before purchasing with a 30-day free trial that includes 25 licenses.

Example 1: CPM and Construction Projects

Imagine you’re building a house, and you have several task sequences already identified and planned out:

Build House

  • Dig foundation – 10 days
  • Build walls – 20 days
  • Build roof – 10 days
  • Install faucets – 2 days
  • Install fixtures – 2 days
  • Install carpeting – 4 days

Finish House
Each task takes a varying amount of time and resources. For instance, building walls and laying the roof will take longer than installing faucets and fixtures.

To determine the critical path of your construction project, analyze the sequence of tasks that will make the most time. This should look something like this:

Build House

  • Dig foundation – 10 days
  • Build walls – 20 days
  • Build roof – 10 days

Finish House
You now know your construction project will take at least 40 days to complete based on this critical path. While you can always undertake several task sequences simultaneously, building your house will take longer than anticipated if there’s any delay in this established critical path sequence.

Example 2: CPM and Research

Here’s a simple research and development project with the following three activities:

  • Activity A: Designing and circulating surveys will take three months
  • Activity B: Gathering data from the surveys will also take three months but cannot begin until Activity A is complete
  • Activity C: Purchasing a software solution will take two months and is independent of both Activity A and Activity B

From the above details, you know the fastest this project can be completed is in six months because Activities A and B are co-dependent, with each taking half that time. Plus, Activity B cannot start until Activity A is complete.

To ensure your R&D project is completed within the six-month timeframe, Activity A must start first so Activity B can start immediately after. Out of all three, Activity C is less critical and can be completed during any two-month window during the six-month timeline.

How to Get Started With Critical Path Project Management

At this stage, you should have an idea of how the critical path project method works and how it will help ensure your projects are completed on time and within budget. Let’s now take a look at how you can start applying this methodology to your projects.

Step 1: Identify Project Activities

Check the work breakdown structure (WBS) or the project scope and details to create a list of specific activities for the project. Don’t worry about adding sequences, as we’ll focus on them in subsequent steps.

Ensure all activities are tagged by name, coding, accounting string, or any other identifier and have a duration or target date if milestones are involved.

Step 2: Logically Sequence and Link All Activities

You must know the sequence of activities to prepare and connect the activity list prepared in Step 1. This is essential to ensure all project milestones are met.

As a project manager, you need to have a thorough understanding of every linked or related activity and show the proper connections in the schedule. Contractors often fail to identify these relationships, which is the main reason behind delays and other problems caused during project execution.

Step 3: Create a Network of All Defined Activities

Summarizing all defined activities and showing dependencies between them is the very foundation of the critical path method.

Keeping that in mind, all critical work sequences must be linked with logical coordination and planning. Additionally, the CPM format should be based on calendar days as the main planning unit. That said, your CPM schedule should avoid using working days since it’s likely to cause confusion and errors.

Step 4: Estimate Project Completion Time

Imagine you anticipate a specific project will take ten days to complete. During the course of the project, you find the third activity on the critical path is delayed by five days. As a result, the project will now take 15 days instead of ten unless another activity on the critical path gets completed five days earlier.

To avoid these delays, you should be very careful when estimating time durations and managing tasks in the critical path.

Your best bet is to use known unit quantities when calculating how long any particular task takes. For example, if you want to know how long it will take to charge 12 phones, find out the total duration for fully charging one.

Use the same logic to estimate the overall task duration. Considering the timeline of similar tasks in the past or asking for supplier quotes with estimated delivery times are two great tactics.

Step 5: Identify the Critical Path

As the name suggests, you’ll learn the longest duration path through your network in this stage.

All activities located on the longest duration part must not be delayed. If they are, you’ll experience a delay in the whole project. Because of its impact on the project, critical path analysis is a crucial part of project planning using CPM.

You can identify the part for each activity using the following parameters:

  • ES—Early Start: Earliest time to start a predetermined task, given that prior tasks must be completed first.
  • EF—Early Finish: Earliest end time for the task.
  • LF—Late Finish: Latest time the task must be completed without delaying the entire project.
  • LS—Late Start: Latest start date that the task must be started without delaying the project.

The critical path is the path through the project network in which all activities have been carried out on time and have never been delayed. In other words, the path for which ES=LS and EF=LF for all activities in the path.

Any delay in the critical part will delay the entire project.

Step 6: Update the CPM Diagram as You Go

Keep updating the critical path as your project develops.

You may find alternative solutions to either accelerate the project or continue the project as projected. You can analyze other critical paths when reviewing all the activities that have already been completed. If you want to create a new path altogether, you can do that, too, as the project moves forward.

Incorporating changes and extra tasks that were not a part of the original critical path is also necessary to present an accurate progress report.

Step 7: Prepare for “What-If” Scenarios

Any experienced project manager knows that things won’t always go as planned. It’s why you should make room for “what-if” scenarios that may take place when mapping out your critical path.

You can always experiment to see the effect potential task delays or setbacks may have on your project’s time frame as the project progresses. Here’s how to go about this:

  • Extending a critical task by increasing its duration: This will display how other critical tasks will be affected when a specific task gets delayed. You can also determine whether other non-critical tasks may gain time because of this, revealing the total slack.
  • Extending a task that has free slack: Slack signifies the total time frame during a task can be delayed without causing any delay in the successor activity—or even the project finish date. Free slack indicates the time one can delay a task without delaying its successor task. Other tasks will remain unaffected when extending a task with free slack until you exceed the free slack available.
  • Extending a task with total slack: This will show you how other tasks will be rescheduled. Total slack is the duration in which a task can be delayed without delaying the project’s end date.

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Bryan Wise
Bryan Wise,
Former VP of IT at GitLab

Incredible companies use Nira