What is the critical path method (CPM)?
The critical path method ensures the effective completion of all the tasks within a project, from start to end. This involves visually planning tasks, scheduling dependencies, and streamlining workflows, all of which lead to the ultimate successful task execution, with the aid of the critical path formula and network diagram.
Also referred to as critical path analysis (CPA), this technique identifies and chalks out the longest string of tasks, also called the critical path. This path's completion is paramount to the successful completion of the project, and delaying it delays the project in its entirety.
To do this, the tasks are categorized into critical and non-critical tasks. Critical tasks hold the most value and take the longest time to complete, whereas non-critical tasks can tolerate some delay and are scheduled flexibly to accommodate scope changes without hindering the completion of the overall project. After identifying and categorizing these tasks, the team determines timelines, and the critical path comes into being.
A project manager overseeing complex projects with numerous dependencies and intricate processes can largely benefit from the workings of the critical path method, as it aids in task prioritization, streamlining of numerous workflows, risk mitigation, and on-time completion of the project.
What is the critical path method in project management?
The critical path method in project management is the longest chain of tasks in the project whose delay would set back the project as a whole. Good project management software can simplify the job by identifying the critical path for you, so you can hit the ground running and get to grips with the critical tasks that warrant your undivided attention.
When should you use critical path analysis?
Projects of complex natures—namely those in the aerospace, automobile, manufacturing, and construction—could benefit from the implementation of a well-oiled critical path analysis framework. Typically, a critical path analysis is performed before the commencement of the project to enable its seamless execution. The project's moving parts are identified, the outline is ironed out for any discrepancies, and the critical path is given structure. When this is done ahead of time, teams dodge risks like budget overruns, resource constraints, and scope changes.
Critical path method vs PERT
PERT chart:
The acronym PERT stands for Program Evaluation and Review Technique, a project management framework employed by businesses handling complex projects of indeterminable duration or project activities whose timelines are not easy to predict.
Largely used in research projects, PERT estimates the least possible amount of time that an activity can take to finish, thereby predicting the least amount of time taken for the project to draw to a close. This technique helps create realistic schedules for projects with uncertain duration, proving to be a probabilistic tool.
An algorithm consisting of three-point estimates is used to arrive at the data for each activity's expected time of completion, which in turn determines the project's completion time as a whole. For this, the project needs to be divided into events and milestones, following which the duration for each task can be calculated, using time or project duration as a variable.
PERT helps projects combat uncertainties owing to time, provides fresh perspectives to project managers for every new project without bias, and helps outline efficient risk mitigation strategies, leading to the effective planning, tracking, and execution of the project.
The critical path method is also a project management technique that is responsible for calculating the least amount of time taken for project completion, but only for projects that work around a predetermined timeline and rigid schedule. The focus in this case is on planning and managing time. The critical and non-critical tasks are charted out, and the estimates for each category are determined.
Although both critical path and PERT follow similar project management techniques, the terms are not used synonymously, as their nuanced differences help them hold their own.
PERT
CPM
Focuses on timeline planning and control
Focuses on efficient time and cost management
Project management technique that estimates time for unpredictable activities in a project
Statistical tool that calculates time and budget for pre-defined activities in a project
Suited for research-based projects
Suited for complex projects like those in construction or aerospace
Event-oriented technique
Activity-oriented technique
Probabilistic model
Deterministic model
It is possible to use both the critical path and PERT in conjunction to plan schedules and predict project completion time. This can help in bringing the project to a smooth closure.
Critical path vs Gantt chart
Gantt chart:
A Gantt chart is the visual representation of a project and its various activities, displayed in the form of bars plotted against the duration of the tasks. Teams use Gantt charts to closely monitor projects at each juncture so they can more efficiently manage tasks.
The critical path method and Gantt charts are project management tools that veer projects towards the path of efficient planning, tracking, and execution, which keeps them on track with their allocated budget and planned completion time. Both techniques serve a similar purpose, but they have a distinct set of markers that set them apart.
Gantt chart
CPM
Visual timeline view of projects plotted against their timeline
Chain of critical tasks dependent on each other that need to be completed on time; delay in completion will cause the entire project to fall behind schedule
Shows progress of tasks, dependencies, and resources
Determines the least possible time for project completion by visualizing critical and non-critical tasks
Plots sequential critical tasks on a graph
Displays sequential critical tasks as a network diagram
While the critical path method draws an outline of important tasks and their duration, the Gantt chart meticulously tracks project progress, dependencies, and schedules. Using the Gantt chart in combination with the critical path method allows you to stay on top of crucial updates, link dependencies, mitigate risks, steer clear of derailments, and take actionable measures.
Explore the components of the critical path method (CPM)
Earliest start time (ES)
This is the earliest time a task can begin in a project.
Latest start time (LS)
This is the latest time a task can begin in a project before potential delays take place.
Earliest finish time (EF)
This is the earliest a task can reach its completion stage in a project, and it's found by considering the earliest start time.
Latest finish time (LF)
This is the latest that a task can be completed in a project, and it's found by considering the latest start time.
Float
Float or slack is the acceptable amount of delay that a task can accommodate before it can threaten to jeopardize the project schedule.
How to determine a critical path in a project
Organize project activities
List all the work items that need to be completed in order to accomplish project goals. Use the work breakdown structure to deconstruct the project into smaller chunks.
Example: For a construction project, this is what the work breakdown structure would look like.
Link dependencies
Identify interdependent tasks (i.e., relevant activities that are reliant on another similar task for completion). Figuring this out before the beginning of the project enables you to create a robust critical path.
Example: In a construction project, project activities come with multiple dependencies that look like this.
Create a network diagram
A critical path or a network diagram can be created at this stage to list out the various project activities chronologically. This takes the form of a flowchart that represents the flow of the tasks and their dependencies.
Calculate project duration
Next, calculate the estimated time for every task to be completed, which can be determined using the critical path algorithm. This algorithm comprises two parts: the forward pass (measured using the earliest start time and earliest end time for each task) and the backward pass (measured using the latest start time and latest end time for each task). Refer to the FAQ section below for a more elaborate description.
It is also possible to calculate the duration using available data from earlier projects and making forecasts based on experience, as well as by taking industry norms into consideration.
Determine the critical path of the project
Once the project duration is calculated, the critical path is formed. Tasks with zero float (the amount of flexibility that a task can have) are considered critical tasks, and these tasks are usually dependent on each other. Tasks that have a float more than 0 (positive float) are non-critical tasks.
Modify as you go
Make incremental modifications to the critical path as you progress through every stage of the project, embracing any kind of revision that the project may warrant with respect to changing scenarios.
Benefits of using critical path method (CPM) in project management
Prompt prioritization
Heavyweight tasks are earmarked and given precedence to ensure minimal delays and seamless execution of critical activities. Prioritization helps teams rectify errors ahead of time, determine the float for every task (critical tasks have zero float; non-critical tasks have positive float), and add a layer of adaptability to the project schedule.
Precision in planning
By utilizing the critical path method and PERT in tandem, teams can perfect their schedules, since they're able to keep an eye out for both predictable and unpredictable activities. Teams respond better to project turbulence, amp up risk strategies in the face of adversities, and leave minimal room for error.
Clear communication
Right from day one, it is necessary to involve the expertise of key stakeholders responsible for the ebb and flow of the project. This includes contractors, employees, project managers, and clients. As a result, project teams can gauge holistic insights and gather vital inputs to steer the project toward an upward trajectory.
Flexible flow
Accommodating scope changes within rigid workflows is a pain, and since changes are inevitable in complex projects, teams that use the critical path method can circumvent unforeseen circumstances and find their way around issues easily, without destroying the overarching scope of the project in the process.
Risk reduction
Teams can predict any risks that may sabotage the project by visualizing timelines and tasks on the Gantt chart. The project manager can tactically respond to such risks and nip them in the bud.
View visually or perceive visually
When used in conjunction with the Gantt chart, the critical path method puts up a visual show, depicting tasks and their duration in a graph-like fashion. Teams are notified of real-time updates at a glance and know how each person's placed for the day, encouraging healthy collaboration.
How to use the critical path method (CPM)
Bringing the critical path method into your project management game provides flexibility when planning schedules, bolsters team collaboration, prioritizes tasks, and ramps up productivity. Here are a few other ways to apply this methodology.
Shrink project schedules
While using the critical path method, there are chances that your timelines could do with a slight compression to arrive at your deadlines as early as possible. Techniques like fast tracking and crashing can be put into effect.
Fast tracking
Here, the expedition of the project can be carried out by glancing at the critical path and choosing activities that can be performed simultaneously. Multiple critical paths can run in parallel and speed things up.
Crashing
To attain the speedy execution of the project, activities need to be completed hastily, which can be done by putting up more resources for the task. This, however, is not an ideal situation to be in as the quality of work is significantly compromised.
Solve resource management challenges
Resource leveling, a technique that helps resolve scheduling conflicts that spring up due to over-allocation of resources or resource bottlenecks (when resources are unavailable), can be implemented so that a project can be completed on time without delays. This technique resolves resource allocation challenges by altering the start and end dates of the tasks, and these changes will be reflected over the critical path.
Steps to determine the critical path with Zoho Projects
Zoho Projects, an intuitive and dynamic cloud-based project management platform, is home to a plethora of tools that make project management—and in our case, critical path management—a breeze. One such tool is the Gantt chart, whose visual depiction capabilities elevate the way you work with critical paths.
We know the grunt work that goes behind manually determining a critical path, and that's why we help you visualize it with a Gantt chart. This way, you can focus on what you need to do: rolling out your projects.
Let's take the construction project example to highlight the steps for establishing the critical path.
Create a project
Create a brand new project from scratch and fill in all the required information.
Add tasks
Once your project is added, start creating milestones, task lists, tasks, and subtasks.
Head to Gantt view
Head over to your tasks and display them in the Gantt view.
Toggle Critical Path and Slack
To view the critical path and the slack/float, toggle the Critical Path and Slack buttons. The string of linked critical tasks will appear on the Gantt chart, highlighted in red.
FAQ
What is the critical path formula?
The critical path formula is used to calculate the critical path of a project. Generally, the formula comprises two parts: the forward pass and the backward pass. The forward pass helps you calculate the earliest start time and finish time of your project; the backward pass helps you calculate the latest start time and finish time of your project.
Forward pass:
To determine the forward pass, the earliest start time (ES) and earliest finish time (EF) for each task is calculated. To do this, find the EF of the previous task, which will give you the ES of the current task (in other words, the ES of the current task is equal to the EF of the previous task). Once you derive the number, add the duration of this task to it. The formula to determine the EF would look something like this:
Early finish = Early start (ES) + time or t (the duration of an activity)
By calculating the EF of the last task of the project, you arrive at the overarching EF of the project.
Backward pass:
To determine the backward pass, the latest start time (LS) and latest finish time (LF) for each task is calculated. The formula for LS is:
Late start (LS) = Late finish (LF) - Activity duration
The above formula fetches your project's latest completion date, giving you more room for flexibility and risk mitigation.
When can you use the critical path method?
The critical path method can be employed to forecast the shortest completion period for a project that has the longest sequence of tasks that need to be completed within the stipulated time.
Why is the critical path important in project management?
Identifying the critical path in project management highlights tasks that are pivotal to the successful completion of the project. It also gives wiggle room to accommodate ad-hoc changes, straightens out complex processes, and streamlines milestones and tasks with multiple dependencies.
Can a project have multiple critical paths?
Projects that fall under the construction, manufacturing, or automotive industry are complex in nature, and they are bound to have numerous critical paths that function concurrently and are aimed at achieving a collective project goal.