Level of Effort Task
Why does my summary task contain more work hours than the total work hours of its tasks?
Many projects are set up in Microsoft Project with resources assigned to the summary task, but few of these assignments are properly understood by the person who originally assigned the tasks. The most common misunderstanding is that the assignment of a summary task simply designates the resource who is responsible for the completion of all work within the task. While this may be the intention of the assignment, it also assigns work to that resource. The work assigned to the resource is NOT simply the total of all work within the summary. In fact, it is ADDITIONAL work to the work within its corresponding tasks. In other words, you not only add up all of the work from the tasks to the summary, but you also add more hours from the summary task to itself. Here's an example.
Task 1 and Task 2 have a total work value of 48 hours. The summary, which calculates to a total duration of four days gets an additional value of 32 hours work assigned to it (one resource is assigned to the summary at 100% allocation in a 40 day work week). As a result, the summary calculates to 80 total hours.
Although this is often perceived as an incorrect calculation by those who have mistakenly applied it, it is correct by design. Resources assigned to summary tasks are assigned as "level of effort" resources. This is considered advanced functionality and is not intended for use by project managers who are not familiar with level of effort work assignments. Those who do wish to assign level of effort calculations to summary tasks will find that it does work quite well.