Summary task shows wrong total duration

Question

Microsoft Project 2013: A summary task shows a wrong total of DURATION HOURS: The sum should be 31 hours, but it shows only 25 hours. However, the sum of WORK HOURS is correct. Also, the calculation of costs is correct. So, somewhere, 6 hours just in the duration are missing.

• The summary task has NO resources assigned.
• The summary task has NO predecessor assigned.
• All tasks below the summary task have the same resource, all at 100% capacity.
• In the tasks below, work and duration are all equal, which is correct.

So what could be wrong ?

Answer 1

If each task has the same resource at 100% and the durations of the subtasks all equal the work, then the only possible explanation for a shorter summary duration is that one or more of the subtasks overlap, which would yield a resource over-allocation.

You can use the Resource Usage view to check this as it will be obvious which tasks are causing the over-allocation and resolve by moving tasks/levelling resources.