How to Calculate Project Duration

by Eric Dontigney; Updated September 26, 2017
Female professor front of a whiteboard

Developing a realistic project schedule requires you to calculate the project duration as accurately as possible. You achieve this by completing time estimates of individual project tasks and activities.

Project Activity Checklist

Create a project activity checklist that includes a list of all of the anticipated activities and tasks, as well as pertinent sub-tasks necessary to complete the project. For example, the task of configuring cloud-based human resources software might include a sub-step for integrating existing data and another for setting user-access levels. The checklist provides a convenient place to input time estimates for each task.

Time Estimates

A project manager with experience often estimates task completion times based on prior, similar projects. If you lack experience as a project manager, or the project represents something new, you should enlist the assistance of those with relevant experience, such as other project managers. Project team members can also provide estimates for their individual activities. Adjust the time estimates up or down for all of the assumptions and constraints you identify. For example, if a team member plans to go on vacation during the anticipated project schedule, that serves as a constraint.

Calculation and Float

Add all of the final task and activity estimates together and convert the total to hours. This number serves as a provisional project duration estimate, which needs to be converted into weeks or months. Project managers often include additional time, called project float, to provide a time buffer for any unexpected delays in completion.

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