Understanding Critical Path in Project Management (Example Included)

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

There are many techniques project managers use to schedule their project activities so that everything lands where it’s supposed to and the project fits the approved timeline. The critical path method is one of these.

What Is the Critical Path Method?

Think of critical path in project management as a project modeling technique. It’s a sequence of stages where you figure out what the least amount of time is necessary to complete a task with the least amount of slack. So, the critical path is really the longest length of time it will take to complete the project tasks.

What we understand as critical path was first developed in the late 1950s by Morgan R. Walker of DuPont and James E. Kelley of Remington Rand. They came upon the tool around the same time as Booz Allen Hamilton and the U.S. Navy were working in a similar vein. The roots of critical path can be found in some practices by DuPont in the early 1940s, and even contributing to the Manhattan Project.

Since that time, the critical path method has been used in a variety of projects, from construction, aerospace and defense to software and product development, engineering, plant maintenance and more. Projects with interdependent activities can benefit from this. While the original critical path program isn’t used anymore, the approach remains the same.

Except today’s critical path is calculated automatically by project scheduling software. That makes the whole method, a whole lot easier.

Critical Path – Definition of Terms

To understand the concept of critical path, you need to understand the various terms used in this method. The critical path is the longest distance between the start and the finish of your project, including all the tasks and their duration, which gives you a clear picture of the project’s actual schedule.

Related: How to Create a PERT Chart

Another term in the critical path method is earliest start date. This is simply the earliest date that a task can be started in your project. You cannot determine this without first knowing if any tasks are dependent on this one task, or figuring out other constraint that might impact the start of this task. Next is the earliest finish date. This being the earliest date your task can be completed.

Along those lines, you need to figure out what the latest start date is. This is the very last minute in which you can start a task before it threatens to upset your project schedule. And you need to calculate what the latest finish date is for the same reason. By having a clear picture of this timeframe, you can better schedule the project to meet its deadline.

Float, also known as slack, is a term that describes how long you can delay a task before it impacts the planned schedule and threatens the project’s deadline. When you are collecting tasks for the critical path, they must have zero float. But if the tasks do have some float, then they go on the non-critical path, which means if this task is delayed the project can still finish on time.

Crash duration is a term that describes the shortest amount of time that a task can be scheduled. You can get there by moving around resources, adding more towards the end of the task, to decrease the time needed to complete the task. This often means a reduction in quality, but is based on a relationship between cost and time.

Components to critical path method

Critical Path: Basic Steps

The technique for figuring out the critical path in your project can be boiled down to four essential steps.

  1. List all the tasks needed to complete the project. You can use a work breakdown structure, which is a hierarchical decomposition of the project, noting every deliverable.
  2. Note the duration of each of those tasks, such as how long each one is going to take to complete it and move onto the next one.
  3. If there are any task dependencies, you want to collect them, too. A task dependency is when one task cannot start until another one has been finished. It’s a key element of good task management.
  4. What are the milestones in the project? That being the major phases. Also, what are the deliverables? Create a list of these.

When you have this data collected, you’re able to calculate the longest path your planned tasks will take to reach the end of the project, as well as the earliest and latest that each task can start and finish without impacting the project schedule.

Therefore, you’re determining what tasks are critical and which can float, meaning they can be delayed without negatively impacting the project by making it longer. Now you have the information you need to plan the schedule more accurately and have more of a guarantee you’ll meet your project deadline.

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You also need to consider other constraints that might change the project schedule. The more you can account for these issues, the more accurate your critical path method 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 with take because of the task and constraint.

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There can be more than one critical path. Also, the critical path can change dependent on your resource scheduling. It can also change over the course of your project.

Monitoring the Critical Path with ProjectManager.com

Monitoring the critical path is a way to make sure your project stays on schedule. You can do this the easy way or the hard way.

The hard way is to create a network diagram that illustrates the activities that are networked together and what their dependencies are. They are pinned to an early or late start date, which allows you to understand the flow of the project. This is a complicated process, but it’s how it has been done since the advent of project management.

But there is an easier way.

In ProjectManager.com, thanks to our advanced Gantt chart, you can automate the calculation of the critical path. Simply go to the Gantt chart view in our online project management software, select the Gantt settings, and then filter to only show the Critical Path Tasks. It’s never been so easy to calculate the critical path.

chart critical path using an online gantt chart

Critical Path Method Example

To see the elegance of the critical path method, let’s take a look at it in action. We’ll just pick a very easy task to help make the process more concrete, such as building a birdhouse.

The first step is to break up the project into tasks. In this case, that would include: designing the birdhouse, choosing where it will be place when done, buying the wood, glue, nails and whatever equipment is necessary, such as a hammer. Then, once the resources are assembled, the build would take place and finally securing it to the site. You should use a work breakdown structure to capture all the steps.

Now comes the tricky part, you want to know how long each task will take. This can be difficult if you’ve not built a birdhouse before and have nothing to base your estimates on. If that’s the case, get advice from others who have, so you can have the most accurate estimation of the duration of the various tasks possible.

It’s time to think about task dependencies. Are there any tasks that can’t start until the prior one is completed? For example, you can’t build the birdhouse until you have a design and materials. Make a note of all dependencies.

What are the milestones in your project? With the birdhouse there is probably three: design, built and erecting it on site. Having milestones helps to keep you on track, so you can make sure you’re meeting your baseline schedule.

The critical path method comes in by calculating the longest time it would take to complete the project. Also, what is the earliest and lasted it would take to complete each task. The point of this, of course, it to see which of your tasks are critical and which can be delayed or floated.

This helps you devise a more accurate schedule and that bird isn’t going to wait forever for it’s new house.

This post was updated November 2019.

If you’re looking to calculate the critical path in your project, then you’re going to need to measure a lot of variables. You’ll need a project management software that can handle those complicated metrics. ProjectManager.com 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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