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Critical Path is a project scheduling technique that determines the shortest time that the current project plan can be completed.

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Quick reference

Critical Path

Critical Path is a project scheduling technique that determines the shortest time that the current project plan can be completed.

When to use

Critical path is used when a project is schedule driven.  In that case the critical path is the prioritization for project tasks. If critical path tasks are delayed, the project is delayed. 

Critical path is very useful when there are multiple parallel project paths.  If the project is a sequential waterfall schedule, critical path provides no useful information since every task is critical.  However, with multiple parallel paths, normally one path will be longer than all of the others – that is the critical path.

Critical path is often recalculated when project changes occur or if non-critical path tasks become very early or late to determine whether the critical path may have changed.

Instructions

The critical path is the most important sequence of tasks for schedule-driven projects.  A delay on the critical path immediately translates into a delay to the end of the project.  The only way to shorten the time on a project is to shorten the critical path.  Reducing time on any tasks that are not on the critical path will speed them up but will not impact the end date of the project.  When trying to complete a project as soon as possible, micro-manage the critical path.

A critical path requires that a complete network diagram is developed with all tasks included and that each task has a duration estimate.  With those two elements of project planning complete, the critical path can then be calculated. 

I normally calculate the critical path when the planning for a phase is being completed.  If the total time is longer than I had allocated for that phase, I investigate the tasks on the critical path and determine how they can be changed to shorten the duration (reduce scope, add resources, change task relationships).  I also will increase the duration estimate of tasks with technical or resource risks that are on the critical path since a problem with that task immediately creates a schedule problem in addition to the technical or resource risk. 

There can be multiple critical paths within a project – when that occurs, the overall schedule risk on the project is increased since either path could lead to a delay in the project completion.

When approaching a major milestone, create or track the critical path that leads to that milestone.  This will minimize the probability of a last minute delay.

Critical Path: “The sequence of activities that represents the longest path through a project, which determines the shortest possible duration.” PMBOK® Guide

This definition is taken from the Glossary of the Project Management Institute, A Guide to the Project Management Body of Knowledge, (PMBOK® Guide) – Sixth Edition, Project Management Institute, Inc., 2017.

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  • 00:04 Hi, I'm Rey Sheen.
  • 00:06 I'd like to talk about a very important element on project schedule planning on
  • 00:10 schedule constraint projects and
  • 00:11 that's the critical path analysis. >> The project management
  • 00:17 body of knowledge, the PMBOK guide >> To find the critical path as
  • 00:21 the sequence of activities that represents the longest path through a project,
  • 00:25 which determines the shortest possible duration.
  • 00:29 That means a critical path is the longest, but
  • 00:31 not necessarily the most difficult of the project paths.
  • 00:35 What counts is duration time.
  • 00:37 Let me show you an example. >> This is a simple project
  • 00:40 network diagram.
  • 00:40 There are a total of eight task of varied duration and
  • 00:43 multiple paths through the network.
  • 00:45 Let's look at each of the three paths.
  • 00:48 If we go along the bottom path, there are three tasks of two days each for
  • 00:51 a total of six days.
  • 00:53 If we start in the middle and then go low, there's one task of one day and
  • 00:57 then two task of two days for a total of five days.
  • 01:00 And three tasks.
  • 01:02 If we follow the middle path, there are three tasks, each of one day for
  • 01:06 a total of three days.
  • 01:08 Finally, if we follow the top path there are only two tasks, the one is for
  • 01:12 four days and one is for three days for a total of seven days.
  • 01:15 That path has a fewest number of tasks, but takes the longest number of days.
  • 01:21 Therefore, it is the critical path.
  • 01:23 Any delay in the critical path delays the project completion
  • 01:27 since all the other paths will complete before the critical path is done.
  • 01:31 The critical path determines the final end date for the project.
  • 01:35 As you might imagined,
  • 01:36 knowing your critical path is very important on schedule constraint projects.
  • 01:41 Critical path is normally calculated using software.
  • 01:45 However, if you intend to sit for
  • 01:46 the PMP exam, you must be able to do these calculations manually, since
  • 01:51 you cannot take any project management software into the test facility.
  • 01:54 I'll show you how to do that in another lesson.
  • 01:58 Let's take a look at how we'd go about determining your critical path.
  • 02:02 In order to calculate the critical path, you must have completed enough of
  • 02:05 your project planning to know the relationships between the tasks.
  • 02:09 And you must have a duration estimate for each task.
  • 02:12 That means you're able to create a network diagram that shows the task and
  • 02:15 relationships like I had on the previous slide.
  • 02:18 If the project is a simple waterfall, meaning you do just one task at the time.
  • 02:23 The critical path analysis doesn't add much information
  • 02:25 because there is really only one path to the project.
  • 02:28 By definition that path is the critical path
  • 02:31 since it's the longest path through the project.
  • 02:33 However when there are many parallel paths
  • 02:36 the critical path analysis will determine which path is the longest and
  • 02:39 therefore which path is one constraining the completion of the project.
  • 02:45 When a project schedule changes, the critical path might change.
  • 02:49 I've burn by this on a project, we are focusing on a critical path and
  • 02:52 trying to accelerate it if possible.
  • 02:54 We were successful accelerating in the critical path but
  • 02:58 another path have been delayed and I wasn't watching it closely.
  • 03:01 So although the original critical path became shorter,
  • 03:03 the actual project critical path had changed and I was managing the wrong one.
  • 03:08 The lesson is that when changes occur, recalculate your critical path.
  • 03:13 I've said that critical path information is very important
  • 03:16 on a scheduled constraint project.
  • 03:18 Let's look at how you can use that information.
  • 03:21 A good project manager manages the highest risk aspects of a project.
  • 03:25 When the primary project constrain is schedule,
  • 03:27 the highest risk aspect of the project is the critical path.
  • 03:30 That is the path that will determine when the project will finish.
  • 03:34 There's no schedule flexibility on the critical path,
  • 03:36 all the other paths have some flexibility to accommodate issues and problems.
  • 03:41 Therefore if a problem occurs on the critical path
  • 03:44 I'll burrow resources from tasks that are under way on non critical path.
  • 03:48 If those tasks are delayed,
  • 03:49 it doesn't automatically mean a delayed to the project.
  • 03:53 But if the critical path is delayed the project is delayed.
  • 03:57 Another use of critical path information is when a project approaches a major
  • 04:00 milestone I calculated and track the critical path into that milestone
  • 04:05 Often little hiccups will occur as we approach the milestone.
  • 04:09 The critical path calculation helps me to understand the impact and
  • 04:12 prioritize the resolution of those problems.
  • 04:16 Finally, critical path information is used to prioritize
  • 04:19 any schedule acceleration techniques.
  • 04:21 I apply selected techniques on the critical path
  • 04:24 to accelerate the ending of the project.
  • 04:27 We'll talk about those more in another lesson.
  • 04:29 Applying the techniques on non-critical path tasks,
  • 04:32 does not help the project complete any faster.
  • 04:35 To accelerate the end of the project,
  • 04:37 you must speed up the critical path. >> Understanding
  • 04:42 which tasks are on the critical path will allow the project leader and
  • 04:45 the core team to make better day to day project management decisions.

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