What Is the Critical Path of a Project?

In project management, the critical path is the longest sequence of tasks that must be completed to complete a project. The tasks on the critical path are called critical activities because if they’re delayed, the whole project completion will be delayed.

Finding the critical path is very important for project managers because it allows them to:

  • Accurately estimate the total project duration
  • Identify task dependencies, resource constraints and project risks
  • Prioritize tasks and create realistic project schedules

To find the critical path, project managers use the critical path method (CPM) algorithm to define the least amount of time necessary to complete each task with the least amount of slack.

Once done by hand, nowadays the critical path can be calculated automatically with project scheduling software equipped with Gantt charts, which makes the whole CPM method much easier.

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Now that we know what’s the critical path of a project, we can learn about the critical path method (CPM), an important project management technique that’s based on this concept.

What Is the Critical Path Method (CPM)?

The critical path method (CPM) is a technique that’s used by project managers to create a project schedule and estimate the total duration of a project.

The CPM method, also known as critical path analysis (CPA), consists in using a network diagram to visually represent the sequences of tasks needed to complete a project. Once these task sequences or paths are defined, their duration is calculated to identify the critical path, which determines the total duration of the project.

CPM History

The critical path method was developed in the late 1950s by Morgan R. Walker and James E. Kelley. The origins of the critical path method are closely related with the Program Evaluation and Review Technique (PERT), a similar method which is commonly used in conjunction with CPM.

Why Is CPM Important in Project Management?

Projects are made up of tasks that have to adhere to a schedule in order to meet a timeline. It sounds simple, but without mapping the work, your project scope can quickly get out of hand and you’ll find your project off track.

Using the critical path method is important when managing a project because it identifies all the tasks needed to complete the project, then determines the tasks that must be done on time, those that can be delayed if needed and how much float or slack you have.

When done properly, critical path analysis can help you:

  • Identify task dependencies, resource constraints and project risks
  • Accurately estimate the duration of each task
  • Prioritize tasks based on their float or slack time, which helps with project scheduling and resource allocation
  • Identify critical tasks that have no slack and make sure those are completed on time
  • Monitor your project progress and measure schedule variance
  • Use schedule compression techniques like crash duration or fast tracking

CPM Key Elements

Before we learn the steps to calculate the critical path, we’ll need to understand some key CPM concepts.

  • Earliest start time (ES): This is simply the earliest time that a task can be started in your project. You cannot determine this without first knowing if there are any task dependencies
  • Latest start time (LS): This is the very last minute in which you can start a task before it threatens to delay your project schedule
  • Earliest finish time (EF): The earliest an activity can be completed, based on its duration and its earliest start time
  • Latest finish time (LF): The latest an activity can be completed, based on its duration and its latest start time
  • Float: Also known as slack, float is a term that describes how long you can delay a task before it impacts its task sequence and the project schedule. The tasks on the critical path have zero float, because they can’t be delayed

Let’s take a look at some critical path examples to better understand these critical path analysis elements.

Critical Path Examples

Here’s an example of a CPM diagram. Although it’s high-level, it can help you visualize the meaning of a CPM schedule. For now, we’ll use this critical path diagram to explain the elements that make up the CPM method.

As you can see in this critical path diagram, project activities are represented by letters and the critical path is highlighted in green. Tasks F, G and H are non-critical activities with float or slack. We can also identify task dependencies between the critical path activities, and also between activities (A, F and G) or (A, H and E), which are parallel tasks.

Here’s another critical path example from Harvard Business Review, which shows a critical path schedule for the construction of a house. Each circle in the CPM diagram represents a project activity, as well as it’s duration, while the bolded arrows link the critical path activities. As projects become more complex, you’ll find more parallel tasks, like in this example.

Critical path schedule example by HBR
Source: Harvard Business Review

How to Find the Critical Path of a Project in 8 Steps

Now that you know the key concepts of the critical path method, here’s how to calculate the critical path in 8 steps.

1. Collect Project Activities

Use a work breakdown structure to collect all the project activities that lead to the final deliverable.

2. Identify Task Dependencies

Figure out which tasks are dependent on other tasks before they can begin. Use your judgment and your team members’ feedback. Failing to define task dependencies correctly makes the critical path method useless.

3. Create a Critical Path Diagram

A critical path analysis chart, or network diagram, depicts the order of activities.

4. Estimate Timeline

To use the critical path method, you’ll need to estimate the duration of each task. Use data from past projects and other sources of information such as subject matter experts.

5. Use the Critical Path Algorithm

The critical path algorithm has two parts; a forward pass and a backwards pass.

Forward Pass

Use the network diagram and the estimated duration of each activity to determine their earliest start (ES) and earliest finish (EF). The ES of an activity is equal to the EF of its predecessor, and its EF is determined by the formula EF = ES + t (t is the activity duration). The EF of the last activity identifies the expected time required to complete the entire project.

Backward Pass

Begins by assigning the last activity’s earliest finish as its latest finish. Then the formula to find the LS is LS = LF – t (t is the activity duration). For the previous activities, the LF is the smallest of the start times for the activity that immediately follows.

6. Identify the Float or Slack of Each Activity

Use this formula to determine the float or slack of each task. Float = LS – ES

7. Identify the Critical Path

The activities with 0 float make up the critical path. All of these critical path activities are dependent tasks except for the first task in your CPM schedule. All project tasks with positive slack are parallel tasks to the critical path activities.

8. Revise During Execution

Continue to update the critical path network diagram as you go through the execution phase.

These critical path analysis steps determine what tasks are critical and which can float, meaning they can be delayed without negatively impacting the project schedule. Now you have the information you need to plan the critical path schedule more accurately and have more of a guarantee you’ll meet your project deadline.

You also need to consider other changes or constraints that might change the project schedule. The more you can account for these unexpected events or risks, the more accurate your critical path schedule will be. If time is added to the project because of these constraints, that is called a critical path drag, which is how much longer a project will take because of the task and constraint.

CPM Training Video

Still have questions about the critical path method? In this video, Jennifer Bridges PMP, explains how to find the critical path using a network diagram.

CPM & Project Management Software

As stated above, the critical path method (CPM) was first invented in the late 1950s. During those times, project scheduling software didn’t exist, and project managers had to calculate the critical path manually.

Fortunately, in our times there are many project management software alternatives that can help with the critical path process. Most of them use Gantt charts to represent CPM diagrams and calculate the critical path, but their feature sets vary greatly. One of the most commonly used project management software to identify the critical path is Microsoft Project. However, it has major drawbacks that make ProjectManager a better choice.

Here are some of the main features that you’ll need as a project manager to properly use the critical path method for your scheduling process.

Must-Have Features of Critical Path Software

Link Tasks and Avoid Bottlenecks

Tasks that are dependent on another need to be a part of your critical path calculation. There are four types: those that are start-start, start-stop, stop-start and stop-stop. By identifying these task dependencies, you can avoid bottlenecks later on in the project.

A screenshot of ProjectManager’s Gantt chart, with lines between the bars that represent task dependencies

Get High-Level View of Your Progress

Dashboards are an essential feature for staying on schedule. They provide a window into the project’s performance and progress by collecting data and displaying it in graphs and charts that show various metrics, such as costs, tasks and more.

A screenshot of a dashboard in ProjectManager

Make More Insightful Decisions

Keeping track of a project as it’s executed is how you stay on track. But if the information you’re gathering is dated, then you’re always going to be playing catch up. With real-time data from a cloud-based critical path software tool, you’re always seeing the project as it currently is.

A screenshot of the gantt chart with columns that show project progress, including cost

Know Your Project Variance

Schedules are always changing as the project is impacted from internal and external forces. To make sure you’re on target, you need to have a feature that is collecting data and displaying project variance, so you can compare the actual progress against where you’ve planned to be.

A screenshot of ProjectManager.com’s variance report

Keep a Record of Your Plan

The critical path helps you plan the project, but once you’ve finalized the schedule, you need to set a baseline. This saves the schedule so you can compare it to your actual progress and know if you’re on time, behind or ahead. Any critical path software should have this feature.

A screenshot of the planned end dates column in ProjectManager’s gantt chart

See Deep Data on Performance

Reports serve two purposes. They take you deeper into the project and expose insightful data on project variance, timesheets and more, which helps you stay on track. Filtering the results and sharing the reports is a great communication tool for stakeholder presentations.

A screenshot of a report generated by ProjectManager.com

How to Find the Critical Path with ProjectManager

Figuring out the critical path by hand takes time, and it must be done throughout the project, which is why using project management software streamlines the process. ProjectManager is an award-winning software that automates the critical path method process for you.

Our online Gantt chart filters for critical path, links dependent tasks and is integrated into a full project management software. Sign up for a free 30-day trial of our software and follow along to build a dynamic Gantt chart and automatically calculate your critical path in a few easy steps.

1. Start a Project with a Gantt Chart

Managing a project on Gantt charts allows you to both plan and schedule in one place. Add your tasks and their durations, and they will automatically appear on a project timeline, allowing you to see your whole project at once.

In the software, upload your tasks manually, or upload a pre-existing spreadsheet. Add task descriptions, deadlines, priority, tabs and assign to one or more team members. We also provide templates to help you get started.

ProjectManager's Gantt chart, showing the critical path of a construction project

2. Add Task Dependencies

In the software, connect your dependent tasks on the Gantt chart by dragging one onto the other. You’ll see a dotted-line indicating that the tasks are linked, and you can then define the type of dependency it is.

3. Set the Project Baseline

Setting the baseline is possible when you have finished making your project schedule, complete with deadlines and cost. The baseline captures your data and uses it to compare against your actual progress.

On the Gantt chart, create your baseline for the project by adding the start date to the task and when it’s due to be completed. These planned start and end dates will be compared to your actual project data and show you whether you’re on target or not.

4. See the Critical Path

Easily find the critical path of your project by using our critical path filter. This helps you know what must be done to complete the project, and shows if you’re experiencing any slippage.

5. Get Your Overview with a Dashboard

Now that you’ve got your project planned out, viewing it from a dashboard is the best way to get a high-level view of your progress.

From the Dashboard view, track if your project is proceeding as planned. Our dashboard monitors several project metrics, such as variance, tasks and more, automatically calculating your data to display it in easy-to-read charts and graphs.

ProjectManager’s dashboard view, which shows six key metrics on a project

6. Report on Progress

Reporting is crucial to pull data from your project and get and share insights into how it’s doing. Reports come in many varieties, which together provide a snapshot of the whole project’s performance.

Easily generate reports on critical path, task progress, project status, costs and more in the software. We do the calculations for you, and you can filter the results to show just what you want to see. Our reporting feature is done automatically with one click.

ProjectManager's project management reports help you keep track of your critical path method

ProjectManager is a cloud-based tool that gets real-time data to determine how accurate your planned schedule is to the actual one, so you can adjust immediately if necessary. See how it can help your project by taking this free 30-day trial.

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