Critical Path Method Essentials
In project management, the critical path is the longest sequence of tasks that must be completed to successfully conclude a project, from start to finish. The tasks on the critical path are known as critical activities because if they’re delayed, the whole project will be delayed. By identifying the critical path, determining the total duration of a project can be made.
Calculating the critical path is key during the planning phase because the critical path identifies important deadlines and the activities which must be completed on time. Once a critical path is determined, a clear picture of the schedule becomes evident.
To find this, project managers use the critical path method (CPM) algorithm to define the least amount of time necessary to complete each task with the least amount of slack.
Once a manual task, but with the availability of project scheduling software the critical path can be calculated automatically.
The critical path method (CPM), also known as critical path analysis (CPA), is a scheduling procedure that uses a network diagram to depict a project and the sequences of tasks required to complete it, which are known as paths. Once the paths are defined, the duration of each path is calculated by an algorithm to identify the critical path, which determines the total duration of the project.
The critical path method (CPM) is used in project management to create project schedules and helps project managers create a timeline for the project. The critical path method includes:
- Identifying every task necessary to complete the project and the dependencies between them
- Estimating the duration of the project tasks
- Calculating the critical path based on the tasks’ duration and dependencies to identify the critical activities
- Focusing on planning, scheduling and controlling critical activities
- Setting project milestones and deliverables
- Setting stakeholder expectations related to deadlines
After making these considerations, insight is gained into which activities must be prioritized. Then it becomes evident of which resources need to be allocated to get these important tasks done. Tasks discovered that aren’t on the critical path are of a lesser priority in the project plan and can be delayed if they’re causing the project team to become over-allocated.
Projects are made up of tasks that must 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 project can get off track.
When analyzing the critical path, pay particular attention closely at the time it will take to complete each task, taking into account the task dependencies and how they’ll impact the schedule. It’s a technique to find the most realistic project deadline. It can also help during the project as a metric to track progress.
Therefore, when doing critical path analysis, finding the sequence of tasks that are both important and dependent on a previous task. Less important tasks aren’t ignored and are part of the analysis; however, they’re the ones which can be jettisoned if time and money won’t permit.
To properly understand the concept of critical path, it is best to understand the various terms used in this method.
Earliest start time (ES): This is simply the earliest time that a task can be started in the project. This cannot be determined without first knowing if there are any preceding tasks, or figuring out other constraints that might impact the start of this task.
Latest start time (LS): This is the very last minute in which to start a task before it threatens to upset the project schedule. Calculate what the latest finish time is for the same reason. By having a clear picture of this timeframe, better scheduling of the project can be covered to meet its deadline.
Earliest finish time (EF): The earliest an activity can be completed, based on its duration and its earliest start time.
Latest finish time (LF): The latest an activity can be completed, based on its duration and its latest start time.
Float. Also known as slack, float is a term that describes how long to delay a task before it impacts the planned schedule and threatens the project’s deadline. The tasks on the critical path have zero float. Either calculate the float using the steps above, or by using project management software. If an activity has a float greater than zero, it means it can be delayed without affecting the project completion time.
Crash duration. This describes the shortest amount of time that a task can be scheduled. This can be achieved 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.
Critical path drag. If time is added to the project because of a constraint, that is called a critical path drag, which is how much longer a project will take because of constraints on tasks in the critical path.
Once the key definitions of CPM are known, here are the steps to calculate the critical path in project management:
- Collect Activities: Use a work breakdown structure to collect all the project activities that lead to the final deliverable.
- Identify Dependencies: Figure out which tasks are dependent on other tasks before they can begin.
- Create a Network Diagram: A critical path analysis chart, or network diagram, depicts the order of activities.
- Estimate Timeline: Determine the duration of each activity.
- Use the Critical Path Algorithm: The algorithm has two parts; a forward pass and a backwards pass.
- Forward Pass: Use the network diagram and the duration of each activity to determine their earliest start (ES) and earliest finish (EF). The ES of an activity is equal to the EF of its predecessor, and its EF is determined by the formula EF = ES + t (t is the activity duration). The EF of the last activity identifies the expected time required to complete the entire project.
- Backward Pass: Begins by assigning the last activity’s earliest finish as its latest finish. Then the formula to find the LS is LS = LF – t (t is the activity duration). For the previous activities, the LF is the smallest of the start times for the activity that immediately follows.
- Identify the Float of Each Activity: The float is the length of time an activity can be delayed without increasing the total project completion time. Since the critical path has no float, the float formula reveals the critical path: Float = LS – ES
- Identify the Critical Path: The activities with 0 float make up the critical path.
- Revise During Execution: Continue to update the critical path network diagram through to the execution phase.
These steps determine what tasks are critical and which can float, meaning they can be delayed without negatively impacting the project by making it longer. The availability of this information needed to plan the schedule more accurately and have more of a guarantee that the project deadline will be met.
Also, considerations of other constraints that might change the project schedule need to be understood. The more these issues can be accounted, the more accurate the 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 will take because of the task and constraint.
Critical path software is used to automatically calculate the critical path in the project schedule. Without using software, managers would have to manually calculate the time-consuming and complicated equation.
Time is one of the triple constraints of a project, so it’s understandable why critical path software has become popular in project management. Any opportunity to gain efficiencies steers the project closer to meeting its goals and objectives.
Since critical path is a very specific technique, critical path software is usually associated with a larger project planning tool that organizes tasks, prioritizes the sequence of activities and other features that go into creating the schedule. One of the most used project management software to identify the critical path is Microsoft Project, although there are many others as well.
Knowing the critical path and having a tool to recalculate it as the schedule evolves over the course of the project is key to getting back on track when behind schedule. More benefits to using critical path software include the following.
- Quick Calculations Save Time and Effort
- Track Progress to Know If You’re Behind
- Recalculate as Project Schedule Changes
- Keep Track of Task Dependencies
- Set Milestones and Save Important Dates
- Get Insightful Data When Planning Tasks
- Create Schedule Baseline for Project Variance
The Critical Path Method (CPM) and the Program Evaluation Review Technique (PERT) are both visual representations of a project schedule, but it’s important to know the differences.
The main difference between PERT and CPM is that PERT was designed to plan projects with uncertain activity times. Therefore PERT uses three time estimates for each task: optimistic, most likely and pessimistic. On the other hand, CPM was designed for projects where activity times are certain.
CPM uses a single time estimate for each task and focuses on the analysis of task sequences to estimate the total duration of a project. Another important difference is that the CPM is used to identify critical activities that must be completed on time to avoid affecting the project’s deadline, which is something that PERT can’t do.
PERT can be used alongside the critical path to help estimate the duration of activities.
The Critical Path Method is one of the many tools that project managers use when creating their project plan and schedule. It informs them on the length of time, the amount of resources and costs associated with each task and the overall project. Once they have this mapped out they can start plotting the timeline in their scheduling software and start the process of managing their project.
Critical path plays an important role in developing a schedule in project management. It is used in conjunction with PERT (program evaluation and review technique) to figure out the longest amount of time that it would take to complete a project by looking at the dependencies and duration of each task involved.
Simply put, using the critical path is a way to order the seeming chaotic complexity of any project. If deadlines are important to getting a project to deliver on time, then the duration of each task must be understood in order to better estimate where those deadlines will land on the project timeline.
Critical path analysis is charting the dependent tasks, which are those that cannot start or finish until another has started or finished. This creates a great deal of complexity, but the analysis is crucial in order to have a realistic schedule. If the project isn’t as complicated, however, it might not require critical path analysis.
The critical path is important when managing a project because it identifies all the tasks needed to complete the project—then determines the tasks that must be done on time, those that can be delayed if needed (due to the triple constraint of time, cost and scope) and how much float there is.
The reason for understanding the critical path in project management is that the more accurate and reliable the data, the better the project timeline, schedule, plan and so forth. The critical path of a project shows not only how long tasks are likely to take but prioritizes them.
When in the middle of a project and it’s running behind schedule, the critical path will show which tasks must be completed and those that can be left undone without negatively impacting deliverables. This could mean the difference between a successful project, and a failed one.
Critical path is also helpful within the project as a measurement of schedule variance. That is, it can help determine which stage of the project compared to where the plan indicated at that time. This information will quickly advise if the project is on target or lagging behind.
Another benefit of using the critical path in project management is that it helps identify and map task dependencies. Not all tasks can be done at the same time. There is an order and often that structure means that some tasks can’t start or stop until another has started or stopped. It can help avoid bottlenecks by map parallel tasks and keep the project moving.
Finding the critical path is a useful tool that project managers use to make better time estimates. It lends itself to complex and larger projects, but it can be a helpful tool no matter the size of the project.
Time is always weighing heavy on a project, and a critical path identifies which of the project tasks are not necessary to end with a quality deliverable. Completing every task is important, but sometimes that’s not possible. Critical path helps determine which are not needed.
Once the critical path is determined, keep returning to the analysis and continuing to crunch those numbers as things change when executing the project. That’s a lot of work, but when used in conjunction with a robust project management software, the first steps towards success have been taken. Let us know your thoughts on the Critical path Method, and how it has assisted you in your projects. All the very best on your project management journey.