Calculating Critical Path
The Critical Path Method (CPM) is one of the best-known and most utilized schedule network analysis techniques. It depends on establishing the longest path in the network diagram. Calculating critical path is therefore part of most PMP exam prep online courses. Most online courses will provide critical path method calculation examples and critical path practice questions.
The study of the critical path for project management is essential. As project managers plan a project, they must come up with the scope of work and the deadlines for each task within the project, as well as the end date for the project as a whole. Critical Path Method calculations allow project managers to understand which work packages are at risk of impacting others (or the entire project) if delayed.
As each activity is completed in a manner that their relationships to the other tasks are ordered by using the CPM, a project manager can calculate the most extensive route to the completion of the project. This provides the project management team with the duration of the project.
By defining Critical Path, providing key points on how to calculate it, and listing the necessary steps to the method, we hope to provide you with the best ways to improve your schedule analysis techniques. Also, understanding the Critical Path Calculation Method is a significant part of your preparation for the PMP exam and including it in your study plan will help ensure your success in passing the PMP exam.
Defining PMP Critical Path PMI vs. Near Critical Path
The definition of the Critical Path Method for the PMI is in the PMBOK, it says it is “the longest duration path through a network diagram, it determines the shortest time to complete the project.” By calculating the longest possible path, you can accurately schedule the activities to get to finish the scope of work.
Each activity, forming at the beginning of the network diagram, is mapped out in its entirety. During this process, all variants and each option for that particular task are determined and the alternative that demonstrates the longest path will be that activity’s critical path.
Near critical path is the path that is closest to the critical path. If, for example, the overall project’s critical path is determined as 24 months or two years, and the next closest project duration from your calculations is 18, the near-critical path would be 18 months. Your research and calculations have not only provided you with the longest path to the end but the next best thing to the critical path.
While Float or Slack is included in the final critical path analysis, it is calculated prior to finalize the network diagram. It is part of calculating the time of a task, along with any delays that may occur. These project delays in the float are delays that are anticipated so that they won’t cause delays in the overall scope or in the other activities within the project. Three forms of the float can be calculated.
1. Total float projects the total delay that any activity can incur while not impacting the overall project’s end date or other significant landmarks within the project. For example, if a task is added to the project and wasn’t included in the original critical path analysis, it’s inevitable that there will be a delay. However, if that delay can’t be offset, it could throw the whole project off balance. Total float is the ability to see how long of a delay any task or activity might cause without impacting the project’s critical path.
2. Free float projects the delay without impacting activities’ early start dates. Each task works in conjunction with the others, their time frames, and restrictions. Free float works with the time that’s been calculated as the soonest date that a task can begin. It is the amount of time a particular activity can be delayed without impacting the early start date.
3. Project Float is the length of time a task can be delayed without affecting the overall project completion date.
The critical path analysis itself should show no floats once it is finalized. Since the PMP critical path activities project the longest path, activities will not have any floats. Slack can negatively impact the critical path activity and correspondingly cause delays in other tasks and the project as a whole.
Calculating an activities float
By subtracting the early start from the late start, or by subtracting the early finish by the late finish of an activity, you can determine the float. So, how is the early start, finish, late start, and finish calculated?
To calculate early start or early finish you start at the beginning of the activity and work out the projected time frame through to the activity’s completion. Late start and late finish start at the end of the task and back to the start.
In accounting, they often add the numbers up and then subtract them back to zero. If there is a remainder, they do it again because they know they missed something. Float is the same principle. Either way will give you the finish to start a relationship, but it’s wise to complete both and compare to eliminate the chance for error.
Important Notes About PMP Critical Path Method
The critical Path Method is essential in the world of project management. This method is also a tool that can be, and is utilized outside of project management. By taking the time to understand various aspects of it, you may find that utilizing it in everyday life can make your world as a whole much less complicated.
- When beginning your analysis, you may find that you have more than one critical path. Each will have the same duration and will require careful monitoring throughout the project. Pay attention to both in order to keep the project on track.
- The more critical paths a project can have, the greater the risk exists for the project. By relying on different critical paths rather than one, each of those tracks can endanger the project schedule. By dividing the focus, project management teams may lose track of important activities and deadlines. This can put the entire project in jeopardy.
- If the PMP critical path changes in the process of the project, it will require updates to the deadlines of all tasks and activities from that point forward. For example: if the near-critical path for a particular activity was 15 days and it was finished two days earlier than the critical path timeline of 17 days, the near-critical path will now be the critical path. This can also change the overall project’s longest path and the scope of work’s critical path as a whole. In other words, consistent and constant updating of the project plan can change the critical path. The project must be checked throughout to keep reaching project deadlines.
- Project delays, weather, supply chain issues, etc., can cause negative float. The goal is always to have no slack or be ahead of schedule, but extensions in prior activities due to delays can lead to the critical path becoming affected. If there is a negative float on an activity it can result in invalid timelines and affect the overall project, costing time and money.
- Compressing or abridging a negative float can help you get the project back on track. If the project gets off schedule, by condensing the remaining tasks and activities, you can shorten their timelines and remain on the path.
- It may be necessary to shorten an activity’s duration within the critical path schedule. Tasks that are closer to their finish date will incur less risk when reducing their duration than tasks that haven’t begun. If you do experience an issue within that task you’ll have more time to address the issue without negatively impacting the remaining activities in the project or the project as a whole.
PMP Critical Path PMP Method Example with Solution
Now that we have the basics, let’s see how we can calculate the critical path within a project. Going through each activity, we will specify the connection between each of them, show how a network schedule is created, create a network schedule, define the critical path, and determine the slack for two of the activities.
This project has 8 activities. Each of the sample activities shows the duration as well as what other activities they correspond to.
- Activity A’s calculated length is 6 days. It is followed by Activity F.
- Activity B’s calculated length is 5 days. Activity B stands alone.
- Activity C’s calculated length is 8 days. Activity C stands alone.
- Activity D’s calculated length is 4 days. It is followed by Activities E and F.
- Activity E’s calculated length is 8 days. It is followed by Activity G.
- Activity F’s calculated length is 7 days. It is followed by Activity B and G.
- Activity G’s calculated length is 5 days. It is followed by Activity H.
- Activity H’s calculated length is 7 days. It is followed by Activity C.
Using the information above we can calculate the critical path of the project as well as the float of activities E and F.
PMP Critical Path PMP Calculation
Each possible path is put into the network diagram. By drawing the network diagram, defining each activity’s path, and projecting those paths from start to finish, we can determine the longest path for the entire diagram providing us with the PMP critical path. Once we have established the critical path, we will find the respective float of activity E.
The first step is to define the connections of each activity in order to construct the network diagram.
- Activity A is followed immediately by Activity F. Activity A will take 6 days. Drawing the diagram, we should have Activity F following Activity A. Then we can specify the finish to start the relationship between F and A.
- Activity B and C are both standalone activities. They have no relationships with other activities. They should be put at the end of the network diagram. Activity B is 6 days and Activity C is 8 days.
- Activity D has two subsequent activities, E and F. Activity D is 4 days.
- Activity E is followed by activity G. Its duration is 8 days.
- Activity F also has two corresponding activities, B and G. Activity F is 7 days.
- Activity G is followed immediately by activity H, and its length is 5 days.
- And Activity H is followed by Activity C, with a length of 7 days.
Now that each of the activities has been defined and we know which activities depend on what other activities, we can construct the network diagram for the project. We can refer back to the list to make sure each relationship is in its proper place from start to finish.
Once your diagram is completed, you can see all of the activities from the very first A until the last one H, how each activity relates to the others, what order they fall within the scope of the project, and how long they will take. This provides you with the longest path and allows you to identify the critical path of the project.
1. In the first path we go from activities D, E, G, H, and end at C. This path’s duration is 33 days in length.
2. The second path follows activities D, F, G, H, and C. This path is 32 days in length.
3. The third path follows activities A, F, G, H, and C. This path is 34 days in length.
4. The fourth and final path follows A, F, and B. The length of this path is 18 days.
The longest path, according to the calculations made above, would be the third path: Activity A, to F, to G, to H, and finally to C. Because it is the longest path, it is the critical path for our network diagram and the project duration is 34 days.
Delays or issues in these activities will have a negative impact for the duration of the project. These tasks are the critical path and have no slack.
We hope this helps you in finding the critical path within your projects. Please reference the PMBOK for additional information.
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