- Jan 06, 2020
Microsoft Project and the Critical Path
In this tutorial, we are going to dive into a technical discussion about Microsoft Project and the Critical Path.
In doing so, I am going to teach you that Microsoft Project does not show the Critical Path. That’s right! You read correctly. Microsoft Project does not show the Critical Path.
Instead of the Critical Path, I am going to introduce you to what Microsoft Project does show you. And these are Critical Tasks.
Many Microsoft Project instructors incorrectly teach that Microsoft Project can show the Critical Path.
And today, we are going to fix this common misconception…
The Critical Path Defined
By definition, the Critical Path is the longest path through the project schedule with the least amount of total slack.
Notice that I did not say that the Critical Path is the path with 0 days total slack.
Most real world projects actually have a Critical Path that has more than 0 days of total slack. We will see that situation in our examples coming up.
The Critical Path is a critical component of the project. This is the path of tasks that is typically driving the project completion date.
As such, project managers should actively manage tasks on the Critical Path by ensuring these tasks start and finish on time. We do this to prevent the project completion date from being delayed.
Because the Critical Path is the longest path though the schedule with the least amount of total slack, a delay of a task on the Critical Path typically translates to a delay in the project completion date.
By actively managing the Critical Path, Project managers can increases the chances of the project finishing on time.
The Misconception about Microsoft Project and the Critical Path
As important as the Critical Path is, it never ceases to amaze me how many people believe that Microsoft Project can show the Critical Path.
Many people were incorrectly taught that Microsoft Project can show the Critical Path by simply applying the Critical filter to the schedule. This is actually not the case.
The Critical filter shows Critical Tasks, not the Critical Path.
What’s the difference? Let’s take a deeper look at this…
Is This Really the Critical Path?
Take a look at the below sample schedule. Can you calculate the Critical Path?
If you said that the Critical Path includes Task 1, Task 2, Task 3, and Task 4, you are correct.
This is the path with the longest duration and the least amount of total slack.
And now let’s apply the Critical filter to see what happens…
Once the Critical filter is applied, we see Task 1, Task 2, Task 3, and Task 4 in the resulting view in Microsoft Project.
Is Microsoft Project really showing me the Critical Path?
This is where the misconception starts. Many people believe that what we saw above means that Microsoft Project shows the Critical Path.
What if we take the same schedule and apply a Start no Earlier Than date constraint to Task 4 that changes the forecasted start date of Task 4 from 1/9/2018 to 1/10/2018.
This is one day later than originally scheduled, as shown below.
If the Critical filter really does show the Critical Path, this simple date constraint assignment to Task 4 should not change what we see when we apply the Critical filter.
After all, the path that includes Task 1, Task 2, Task 3, and Task 4 is still the longest path through the schedule with the least amount of total slack. This fact has not changed.
So let’s see what the Critical filter shows us with this new date constraint assigned to Task 4…
Once we apply the Critical filter, we see that only one task is shown in the resulting view. Only Task 4 is shown.
Does that mean that the Critical Path only includes Task 4 now?
Absolutely not! The Critical Path is still Task 1, Task 2, Task 3, and Task 4.
So what happened?
Critical Filter / Critical Task Settings
Many Microsoft Project instructors incorrectly teach that the Critical filter is used to show the Critical Path. As we saw above, this is simply not true.
In the typical training environment, project schedules have no date constraints or deadlines applied. If we apply the Critical filter in these situations, it could look like Microsoft Project is showing the Critical Path, just as we saw earlier.
But as we saw, assigning one date constraint to the schedule drastically changed what we see when we apply the Critical filter.
It all points back to how the Critical filter is built and what it is doing.
If we look at the definition settings of the Critical filter below, we see that this filter is built to show tasks that are tagged ‘Critical equals Yes’.
And if we then look at our project options on the Advanced tab, we see that Critical Tasks are defined by default as tasks that have 0 days or less total slack.
This means that the Critical filter is showing us tasks that have 0 days or less total slack. These are what Microsoft Project defines as Critical Tasks.
There is no path trace occurring and no duration values being counted. Microsoft Project is simply looking at the total slack value of each task to make a determination on which tasks are Critical Tasks and which tasks are not.
Before moving on, I do want to note that you could modify the value used to define Critical Tasks in the Microsoft Project options to something other than 0.
While I would not recommend modifying the total slack definition of Critical Tasks, if you do decide to do this, keep in mind that it still does not change the fact that Microsoft Project is showing Critical Tasks, not the Critical Path.
More on Critical Tasks
Now that we have an initial understanding of Critical Tasks, let’s dig deeper into how tasks become Critical.
We just saw that Critical Tasks are tasks that have 0 days of total slack or less. The amount of total slack is the single factor that determines whether a task is Critical or not.
Did you know that there are ways that we can add or remove total slack from our tasks in the schedule? Let’s look at a few examples…
Example 1: Adding Total Slack with a Date Constraint Assignment
As you saw above, we added total slack to our schedule by adding a date constraint to a task. We assigned a Start No Earlier Than date constraint to Task 4.
This date constraint resulted in the forecasted start date of the task being pushed into the future one day thereby adding one day of total slack to Task 4’s predecessors.
The result? This one day of total slack that was added to Task 4’s predecessors caused Task 4’s predecessors to no longer be tagged as Critical.
And when the Critical filter was applied, any task that had more than 0 days of total slack was not shown in the resulting view.
Example 2: Removing Total Slack with a Deadline or Date Constraint Assignment
Now let’s look at how total slack can be reduced.
Taking a look at our schedule above again, let’s see what happens if we assign a Deadline to Task 5 that is equal to its forecasted finish date.
Once the Deadline is set, the total slack value for Task 5 is recalculated to be 0 days.
The result of this change is that Task 5 is now considered Critical.
And if we apply the Critical filter, Microsoft Project will now only include Task 4 and Task 5 in the resulting view as shown below since these two tasks are the only two that have 0 days or less total slack.
It goes without saying that Task 5 is NOT on the Critical Path, further reinforcing the point that Microsoft Project does not show the Critical Path but rather Critical Tasks.
We could also achieve the same effect if we assigned a Must Start On or Must Finish On date constraint to Task 5. These two types of date constraints force the total slack value of the task to 0 days instantly making the task critical.
And finally, the use of the Finish No Later Than and Start No Later Than date constraints can also result in total slack values of 0 days or less if the constraint date is breached by the task they are assigned to.
What We Should See
Regardless of how many deadlines or date constraints we apply to our schedule, the Critical Path will remain as Task 1, Task 2, Task 3, and Task 4.
This path remains the longest path through the project schedule with the least amount of total slack.
We should see the the below view when looking for the Critical Path in Microsoft Project.
Unfortunately, it is often very difficult to find the Critical Path in Microsoft Project without specialized tools such as Project X-Ray, especially in large schedules.
See our other tutorials on Project X-Ray for more information on how Project X-Ray can help you find the Critical Path and how you can get other valuable insight out of your schedule.
Are Critical Tasks Important?
Critical Tasks are absolutely important! By default, Critical Tasks are those tasks that have 0 days or less total slack.
This can only mean one of three things. A task could have 0 days or less total slack if:
- The task really is on the Critical Path and it has no available slack to be delayed without impacting the project completion date. A delay of this task will impact the project completion date.
- The task is on a path that has a deadline assigned, and that deadline is at risk of being breached or has already been breached if the total slack value is less than 0 days.
- The task is on a path that has a date constraint assigned, and that date constraint is at risk of being breached or has already been breached if the total slack value is less than 0 days.
The key take-away is that Critical Tasks really are critical. They are either driving the project completion date, or they are critical because of an assigned deadline or date constraint in the schedule that is at risk of being breached or has already been breached.
This is very valuable information for the project manager, especially if deadlines and date constraints are traceable back to contractual deadlines and other external factors that are outside of the project manager’s control.
In this tutorial, we learned that Microsoft Project does not show the Critical Path. It shows Critical Tasks.
And we learned that Critical Tasks are important. Critical Tasks have 0 days or less total slack for a reason!
By actively managing Critical Tasks, you can work to prevent deadlines or date constraints from being breached, saving money and reducing the time required to implement schedule recovery plans.
Want to learn more? Check out other similar tutorials:
Total Slack Redefined in Microsoft Project – CLICK HERE
Project X-Ray Critical Path and Driving Path Traces – CLICK HERE