Summary Task versus Milestone

BY: Collin Quiring

This is a quick primer on the difference between a summary task and a milestone task. 

In the Project Management Body of Knowledge (PMBOK), version four, the term “Summary Activity” is defined as:  “A group of related schedule activities aggregated at some summary level, and displayed/reported as a single activity at that summary level.”  And, a “Milestone” is defined as “A significant point or event in the project.”

A milestone is usually used to indicate when a specific phase or group of tasks is to be completed.  It can be considered a deadline date.  It is possible to have numerous milestones in a schedule.  While a milestone can be assigned a resource that is responsible for its completion, it is more common to use the milestone without resources.  This is because the milestone is often a successor to a number of other tasks that all have to be completed prior to its completion.

In Project Professional, a milestone is what the system automatically creates when a task is given a zero duration.  To add a deadline date to the milestone task there is an option to add that date in the task information.

A summary task is just that – a task that summarizes another set of tasks.  Normally, the summary task is not assigned a resource.  This is because the summary task’s start and completion dates are derived from the earliest subtask’s start date and latest subtask’s finish date.  As each task is completed, the summary task’s overall completion is updated as well.  Normally, a summary task is not linked to other tasks.  Using summary tasks makes reading a WBS (Work Breakdown Structure) easier when using a logical grouping.  Creating a WBS usually involves determining the summary tasks and then the subtasks to complete them but it is possible to put all the tasks into a WBS and then determine the summary  tasks later.

In Project Professional, the subtasks are indented and that makes the summary task bold and outdented.  Many levels of summary and subtasks can be created.

Just as a reference point, here are the definitions as defined by Microsoft.  For Microsoft Project, a milestone is defined as: “A milestone is a reference point that marks a major event in a project and is used to monitor the project’s progress. Any task with zero duration is automatically displayed as a milestone. You can also mark any other task of any duration as a milestone.”  And, a summary task is defined as: “When organizing the tasks for a project, you can group the tasks that share characteristics or that will be completed in the same time frame under a summary task….You can use the summary tasks to show the major phases and subphases in the project. Summary tasks summarize the data of their subtasks, which are the tasks that are grouped beneath them.”

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