Critical Path Method (CPM): What's It's, Why It's Important, What's the Use, How to Make CPM Chart and Much More? Tips to Discover, Apply and Succeed in Project Planning!!
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. It 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 ensure those are completed on time
- Monitor your project progress and measure schedule variance
- Use schedule compression techniques like crash duration or fast tracking
Activity-on-Node network diagram:
- A project network should have only one start node
- A project network should have only one end node
- A node has a duration
- Links normally have no duration
- “Precedents” are the immediate preceding activities
- Time moves from left to right in the project network
- A network should not contain loops
- A network should not contain dangles
- Activity label is the name of the activity represented by that node.
- Earliest Start is the date or time at which the activity can be started at the earliest.
- Earliest Finish is the date or time at which the activity can be completed at the earliest.
- Latest Start is the date or time at which the activity can be started at the latest.
- The latest Finish is the date or time at which the activity can be finished at the latest.
- Float is equal to the difference between the earliest start and latest start or earliest finish and latest finish.
Stage 1:
Find the critical path in a project:
- Step 1: Identify all tasks required to complete the project
- Step 2: Determine the sequence of tasks
- Step 3: Estimate the duration of each task
- Step 4: Draw a network diagram
- Step 5: Identify the critical path
- Step 6: Calculate the float
- Step 7: Monitor the critical path
Stage 6.
Calculate the float
Float, or slack, refers to the amount of flexibility of a given task. It indicates how much the task can be delayed without impacting subsequent tasks or the project end date.
Finding the float is useful in gauging how much flexibility the project has. Float is a resource that should be used to cover project risks or unexpected issues that come up.
Critical tasks have zero float, which means their dates are set. Tasks with positive float numbers belong in the non-critical path, meaning they may be delayed without affecting the project completion date. If you’re short on time or resources, non-critical tasks may be skipped.
Calculating the float can be done with an algorithm or manually. Use the calculations from the section below to determine the total float and free float.
Total float vs. free float
Here’s a breakdown of the two types of float:
Total float: This is the amount of time that an activity can be delayed from the early start date without delaying the project finish date or violating a schedule constraint. Total float = LS - ES or LF - EF
Free float: This refers to how long an activity can be delayed without impacting the following activity. There can only be free float when two or more activities share a common successor. On a network diagram, this is where activities converge. Free float = ES (next task) - EF (current task)
Critical path methodology provides visibility into your project’s progress, allowing you to monitor tasks and their completion times. Below are some additional applications of CPM.
Compress schedules
Though not ideal, there are times when project deadlines may be pushed up. In those situations, there are two schedule compression techniques you can use: fast tracking and crashing.
Fast tracking: Look at the critical path to determine activities that can be performed simultaneously. Running parallel processes will speed up the overall duration.
Crashing: This process involves allocating more resources to speed up activities. Before obtaining more resources, make sure that they are still within the project scope and let the stakeholders know of any changes.
Having the critical path plotted out can help you choose the appropriate strategy to meet updated deadlines.
- Effective Scheduling. As noted at the outset, an underlying process of the critical path is the segregation of critical and noncritical tasks. ...
- Enhanced Project Management.
- Distribution of Human Resources as required activity wise
- Budget and Cost Control.
- Past Clients appreciate about timelines
- More quick additional Services.
- Visual impact
- Bigger adaptability
- Early detection of time consuming activities
- Stronger communication
- Easy prioritization
Here is a list of 10 CPM Disadvantages:
- In a big project, a CPM can become extremely complicated and difficult to fathom for the new recruits to the project team.
- If the project is far too bulky and lengthy, the Critical Path Method requires software to monitor the plan.
- CPM can become ineffective and difficult to manage if it is not well-defined and stable.
- It cannot effectively handle sudden changes in the implementation of the plan on ground. It is very difficult to redraw the entire CPM chart if the plan of the project suddenly changes midway.
- The Critical Path Method cannot form and control the schedules of the persons involved in the project.
- The allocation of resources cannot be properly monitored.
- The critical path of the CPM of a big project is not always clear. The project managers have to spend a lot of time to calculate it carefully.
- The Critical Path Method takes longer to identity and to monitor the critical path when the project is of big dimension.
- Using CPM, identifying and determining a critical path is difficult when there are many other similar duration paths in the project.
- At times, to design a CPM is time consuming. It is also difficult to estimate the activity completion time in a multidimensional project.
- Collect Project Activities. Use a work breakdown structure to collect all the project activities that lead to the final deliverable.
- Identify Task Dependencies.
- Create a Critical Path Diagram.
- Estimate the Timeline.
- Use the Critical Path Formula.
- Identify the Critical Path.
- Revise During Execution.
As you manage your project, you may also run into resource constraint issues that could change the critical path. If you try to schedule certain activities at the same time, you may find that you need more people than are available. As a result, those activities will need to be rescheduled. Resource leveling is the process of resolving these conflicts.
Resource Leveling and Expansion
With resource leveling, you can resolve conflicts over allocating resources. A resource-leveled schedule may include delays due from resource bottlenecks (a resource being unavailable at the necessary time).
Resource leveling may also result in a previously shorter path becoming the longest or most “resource critical” path. This happens when the tasks on the critical path are affected by resource constraints.
A similar concept is called the critical chain, which protects activity and project durations from unexpected delays due to resource constraints.
Assessing the Final Project
These scenarios demonstrate all the unexpected changes that can occur when managing a project, and how they can affect the critical path. While things are always subject to change, the good news is that you can measure the variance from your original project schedule and track how it impacted your final project.
Flexibility and Assessing Delays
A schedule created from the critical path method naturally involves a lot of fluctuation because you have to use best-guess estimates to calculate time. If one mistake is made in activity completion time, your whole critical path schedule could change. Or, you may need to purposefully delay project activities due to resource constraints.
Sorting out these delays and determining what caused them can help you avoid similar issues in the future. An important part of your post-project plan is the As Built Critical Path, which analyzes the specific causes and impacts of changes between the planned schedule and actual schedule implemented. The As-Built Critical Path is a schedule that shows the dates that the activities actually occurred and allocates time by determining the responsibility for the delays on the critical path.
CPM, which stands for Critical Path Method, is an algorithm of resource utilization that schedules project activities. CPM is used to construct a project model that includes:
- A task list required for project completion.
- Task dependencies.
- An estimated duration of time for each activity to be completed.
What is the critical path formula?
The critical path formula consists of two parts: the forward pass and the backward pass. The forward pass calculates the earliest start times (ES) and finish times (EF) for each activity, with EF determined by adding the activity's duration (t) to its ES.
EF = ES + t (the duration of an activity)
The backward pass determines the latest start times (LS) and finish times (LF), setting the LF of the final activity equal to its EF and finding the LS by subtracting the activity's duration from its LF.
LF – t (the duration of an activity)
When can you use the critical path method?
You can use CPM during the planning phase of a project to identify the longest sequence of dependent tasks and calculate the shortest possible completion time. CPM is particularly useful for optimizing schedules for complex projects with multiple activities, milestones, and task dependencies.
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