Learn How to Determine a Project Timeline with the Critical Path Method (CPM)

Learn How to Determine a Project Timeline with the Critical Path Method (CPM)
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Projects in business are often comprised of several concurrent series of sequential activities, each of which features its own requirements for time, materials and labor. Well-planned projects, with quantifiable and measurable timelines, have a better chance of success than projects with little or no advance planning. The Critical Path Method (CPM) is used to determine a total project timeline by taking all of the project’s various steps into account. Knowing how to determine a project timeline with CPM can make your project plans more reliable and accurate.

Process Flowchart

The first step in determining the critical path of a project is to construct a process flowchart. Flowcharts can be as simple as paper-and-pencil drawings, or as advanced as multi-layered computer-assisted designs or even mind maps. Project planners represent each activity in a project as a box, diamond, circle or other shape, referred to as a node. Planners connect each sequential node with arrows showing the flow of material inputs, beginning on the left of the flowchart and moving to the right. Concurrent series of steps are drawn above and below each other, and are organized according to the total project timeline flowing from left to right.

Flowcharts should include at least two types of nodes: process nodes and decision nodes. Process nodes include all regular activities that move the project one step closer to completion. Decision nodes are points in the project where the flow of work could go in one of several directions. A quality audit checkpoint is an example of a decision node; if a work in progress passes a quality checkpoint it moves on to the next activity, otherwise it returns to a previous step.

Time Requirements

After completing a basic process flowchart, the next step in finding the critical path and determining a project timeline is to calculate the shortest and longest possible completion times for each activity. Use past data and consult employees with experience in each activity to determine the shortest and longest completion times. Beginning with the first activity and moving forward, project planners determine the earliest and latest possible completion times for each activity, in terms of the entire project timeline, based on their individual completion times and those of preceding activities.

For example, if the first activity’s shortest completion time is seven minutes, then the next activity’s earliest start time is seven minutes into the project.

Critical Path

If a project only requires a single series of activities, the earliest and latest completion times for the project can serve as the overall project timeline. If the project involves several concurrent series of activities, the series with the latest of the latest possible completion times most likely contains the critical path.

The critical path is the sequence of activities in the project which has no slack time, meaning each activity must be completed before its latest possible completion time to keep the project on schedule. Other series can fall behind their own latest completion time estimates; since the critical path is generally the longest series, it leaves room for error in other series. The earliest and latest possible completion time for the critical path can be used to accurately determine a project timeline.


Net MBA: Critical Path Method retrieved at https://www.netmba.com/operations/project/cpm/

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