# Difference Between Cpm And Pert

tl;dr
CPM is a deterministic approach that relies on accurate estimates of task durations, while PERT is a probabilistic approach that accounts for uncertainty and risk.

CPM and PERT are two popular project management techniques used in the construction industry to manage large and complex projects. Both techniques are used to schedule and organize the tasks required to complete the project, but they have several key differences that set them apart. In this article, we will explore the differences between CPM and PERT in detail.

CPM stands for Critical Path Method, while PERT stands for Program Evaluation and Review Technique. Both techniques were developed during the Cold War by the US Department of Defense to manage complex projects such as missile defense systems and space programs. The techniques were later adopted by the construction industry and are now widely used in many other industries.

The Critical Path Method (CPM) is a project management technique that schedules individual tasks with their interdependencies and durations in order to determine the critical path. The critical path is the longest sequence of tasks that must be completed within the time frame designated for the project. The critical path determines the minimum duration required to complete the entire project.

Program Evaluation and Review Technique (PERT) also schedules individual tasks with their interdependencies and durations. However, PERT uses a probabilistic approach based on three estimates of task duration – optimistic, most likely, and pessimistic. These estimates are then used to calculate the expected duration for each task, and the expected duration is used to determine the critical path.

One of the main differences between CPM and PERT is the way they handle task durations. CPM assumes a deterministic approach, where each task has a fixed duration that is known with certainty. This means that CPM relies on accurate estimates of task durations and is less flexible when there are unexpected delays or changes. PERT, on the other hand, takes a probabilistic approach that accounts for uncertainty in task durations. By using three estimates for each task, PERT can calculate an expected duration that takes into account both the most likely and worst-case scenarios.

Another important difference between CPM and PERT is the way they handle the critical path. In CPM, the critical path is determined by the longest sequence of tasks that must be completed within the time frame designated for the project. This means that the critical path is fixed and cannot be changed unless task durations or dependencies are altered. In PERT, the critical path is determined by the tasks with the highest expected duration. This means that the critical path can change as task durations are updated and new information is obtained.

CPM and PERT also differ in the way they handle slack time, which is the amount of time that a task can be delayed without affecting the overall project duration. In CPM, slack time is calculated as the difference between the latest start time and the earliest start time for a task. This means that tasks with no slack time are critically important and cannot be delayed without affecting the entire project timeline. In PERT, slack time is calculated as the difference between the latest expected completion time and the earliest expected completion time for a task. This means that tasks with a short expected duration and a large amount of slack time may be less critical and can be rescheduled if necessary.

Another important difference between CPM and PERT is the way they handle risk management. CPM focuses on identifying and mitigating risks through risk analysis and contingency planning. PERT, on the other hand, focuses on managing uncertainty through probability analysis and risk modeling. This means that PERT is better suited to projects with a high level of uncertainty or risk, while CPM is better suited to projects that are more predictable and have fewer unknowns.

In summary, CPM and PERT are two popular project management techniques used in the construction industry to manage large and complex projects. Both techniques are used to schedule and organize the tasks required to complete the project, but they have several key differences. CPM assumes a deterministic approach to task durations and critical path analysis, while PERT takes a probabilistic approach that accounts for uncertainty and risk. CPM relies on accurate estimates of task durations and is less flexible when there are unexpected delays or changes, while PERT can calculate an expected duration that takes into account both the most likely and worst-case scenarios. CPM focuses on identifying and mitigating risks, while PERT focuses on managing uncertainty through probability analysis and risk modeling. Ultimately, the choice of which technique to use will depend on the specific needs and requirements of the project.