Critical Path Method (CPM)

Updated at: 24 January 2025

The Critical Path Method (CPM) is one of the ways of modeling any project. In fact, it is the longest possible sequence of interdependent operations, the execution of which directly affects the duration and success of the entire project.

What is the Critical Path Method with simple examples?

Let's define the terms right away. CPM and CRM should not be confused. While CPM is a diagram of the best path to a goal, taking into account critical operations, CRM is a software environment for automating customer interactions.

To better understand what the critical path method is for, we can consider an example from everyday life. After all, purely intuitively to perform specific tasks, our brain every time builds a consistent scheme for solving a problem. Moreover, if it is properly prioritized, the more complete, flexible and clear it is, the more successful the result is.

Consider, for example, trivial for interior design process - decorating the wall with a picture. The simplest variant of the scheme of actions looks like this:

Choosing a place → buying self-tapping screws → choosing a picture → drilling a hole → screwing in a self-tapping screw → installing a picture.

This scheme clearly shows the relationship between the elements of the mini-project and highlights those tasks that can not be solved without performing the previous one. For example, you can't screw in self-tapping screws if you don't have them and you can't make a hole in the wall if the drill bit is broken.

The choice of place - completely independent of the resource base action, is a free choice of your design ideas. Therefore, many people start with it. But for real aesthetes or collectors, the most important is the picture, and the place is chosen already under it. Therefore, in this case, the critical path begins with the purchase of the picture, and all subsequent operations depend on its characteristics and parameters. If you first buy and screw in the screws, and then go to choose a picture, you will have to focus not on your taste and interest, but on whether the screws already screwed in will withstand the weight and size of the acquisition. Therefore, a more logical scheme would be this:

Choosing a picture → choosing a place → buying self-tapping screws → drilling a hole → screwing in a self-tapping screw → installing the picture.

In such a variant, there is a clear connection of procedures that will ensure the greatest success of the project.

It is also important to analyze the available resources. Perhaps there are not enough of the right tools, then another item like buying a drill or screwdriver will be added to the plan. Of course, at home the process can be stretched in time, but sometimes life puts specific deadlines, for example, to hang a picture by a certain date of anniversary, celebration or holiday. In business, the time factor is one of the most significant, and in CPM it is determinant. It is not without reason that the method is attributed to the function of project time management as one of the key ones.

## Why use the critical path method?

As a business expands and new structures and tasks are introduced, it requires clear goal setting, a thorough analysis of resource and information capacity, and the establishment of initial and final deadlines for the entire project and its constituent operations. This is necessary to change the direction of the business, to prevent brand collapse, to develop and manage new projects.

All these processes actually represent a time plan-scheme of any project and business development, which is based on a mathematical algorithm. It is for competent management that SRM is used.

The main principles of CPM

These principles are so simple and logical that they are considered basic for other methods of network planning. Among them we can emphasize the following:

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Visuality, or visibility. This is achieved by using charts, graphs, and diagrams.
It is possible to do it in Excel or in software for visualization of SRM like Worksection.

Temporality, or time frames of execution of both the project as a whole and individual stages of the critical path in their interdependence with each other
.

Predictability. It is quite difficult to foresee all possible nuances and deviations from the schedule, but to control the implementation of planned activities and their timing will help the so-called checklist. A check list is a check list of actions with a verbal description of the task stages set before the performer, the terms of their fulfillment and a box for marks of fulfillment.
By analyzing the checklist, you can find out at what stage of implementation the task is and adjust further actions to finish everything in the planned time.

Prioritization, i.e. determining the importance and priority of project tasks.

Flexibility. If we are dealing with complex but predictable projects, the critical path method works well. Unfortunately, life, the market, competitors or the vagaries of nature often make changes to it. Therefore, the path should be constantly monitored and, if necessary, resources should be adjusted and time frames should be shifted at the expense of other operations.

The critical path method is designed for projects of increased complexity, but with good predictability. In reality, such projects are rare. The schedule and plan generated by the SRM method very rarely materialize as intended. Any delay in a single operation shifts the deadline date of the entire project. Other requirements or resource constraints may appear. The only way to compensate for these is through proper calculation and the possibility of correcting the critical path by introducing a time margin for operations.

How to find and calculate the critical path in a project?

It is impossible to calculate the critical path even if you blindly copy it from a successful project, simply replacing the initial data with your own. Studying other people's successful experience will only help you to understand the essence of the critical path method, but not more. For example, the experience of Steve Jobs in the triumphant return of Apple to the leaders of the global electronics and software market is very revealing. By the way, by the end of 2023, it had reached the second place in the ranking of the 500 most influential global brands.

But every project and product has its own peculiarities that should be taken into account when looking for a critical path. Every entrepreneur and business has its own path in their projects, as there are completely different production processes and technologies, equipment, materials, available and required additional resources, availability of highly qualified personnel, timeframes and final goals.

We have already described the basic principles of the critical path method, now let's consider step-by-step the "recipe" for its development:

Compiling a list of tasks, or activities, that need to be accomplished to successfully complete the project within the planned timeframe. This should be done by project managers and leading specialists of the company. By the way, their selection can be one of the first tasks of the project. For example, Jobs in 1997, this is where he started, introducing into the project "his" people, aimed at the revival of the company and professionals in their work. The work breakdown structure is the basis for calculating the entire PMS.
Tasks should be clearly formulated, coordinated in sequence and highlighted with a letter or numeric code.

Identify links between tasks, some of which cannot be solved without performing the previous task, while others can be solved in parallel. This is important for better utilization of resources (human and material) as well as setting deadlines for each task. Thus, there may be one or more branches from the critical path, but it is the longest chain of tasks that will be the main direction on which project schedule management depends. At this stage of the critical path calculation, a dependency graph can be introduced into the list.
For example, operation B depends on operation A, C on B, and D can be performed in parallel, independent of other tasks.

Creating a network grid with the chronology of task solutions introduced into the list. At this stage the list is supplemented with time frames and can be presented already in graphical form on diagrams of two types:

Gantt chart. It is a kind of a roadmap of the project implementation, in the left part of which there is a list of tasks, and in the right part there is a timeline with monthly or other time breakdown. Each task corresponds to a strip of a certain color, the length of which reflects the time interval of its solution. It gives a visual representation of the timing of the work, and in advanced versions and the relationship of operations, as well as data on their performers.
Gantt chart is relevant for tracking the project realization, control over its separate elements and timely elimination of risks of failure of its deadline.

PERT chart. Similar to the Gantt chart, but of a different visual structure. If the Gantt chart is a classic bar chart, PERT is a flowchart, the drawing of which requires several mandatory steps, including the definition of project tasks, their dependence on each other and the terms of realization. The time intervals of each task are calculated in this diagram by the formula PERT: (O + (4 × H) + P) /6, where O is the estimated minimum time (optimistic) of task realization, P is the pessimistic maximum and H is the most probable. Units can be expressed in minutes, hours, days, weeks and even months. The main elements of the chart are nodes (key task blocks), individual tasks within nodes and links represented by arrows on the chart. It should be borne in mind that the connection between tasks does not always imply their resource dependence. For example, launching a new product and developing its landing page on the web are related but not dependent on each other.

Introducing chronology into the SRM task list requires an estimate of the realistically reasonable duration of each operation. This can be done using your experience and expertise, findings from a previous project, or industry standards. The difference between SRM and PERT is not only visual, but also fundamental - if in the first case work with already calculated terms of tasks, in the second intervals are only estimated by probability. The Gantt chart organically complements the SRM by introducing a time scale, but without the division into critical and non-critical paths. Together, they allow you to track and control the management of project timelines in dynamics, in the most complete and accurate way.

How to use the critical path method in practice

The critical path method is used to control the fulfillment of work tasks for project implementation, as well as for other tasks:

Accelerating project completion dates due to changed circumstances.
It is achieved by analyzing the path with the transfer of separate sequentially performed works into the category of parallel ones, performed simultaneously with the critical points of the project.

Resource reinforcement with the increase of the resource base of specific tasks. It is desirable to keep within the limits of the overall project funding. This will help to compress the timeframe of one task when another goes beyond the set timeframe. For example, if there were delays in the supply of materials during repair work, they can be compensated for by accelerating other preparatory work by intensifying the process or attracting additional workers.

By calculating the critical path, you can optimize the process of correcting deadlines and solve the problem of resource shortages by reallocating resources. CPM will help:

Determine the importance of tasks within the project.

Allocate time reserve for critical operations (that's why the longest sequence of tasks is chosen).

Manage the timing of individual project elements in order to finish the project at exactly the planned time.

It should be said that the critical path is not a static form or a dogma that is blindly followed without taking into account changed realities. Its meaning of project management would not be realized if it were not for the possibility of dynamic development. CPM is really just a path indicated on a map, not a specific road with its pleasant and unpleasant surprises. But without this guide, you can get tangled up in the maze of important and unimportant activities and even get off the main highway.