What you are expecting is not how the Duration column works for summary tasks (which you describe as a sub category). For a summary task, Project for the Web calculates the Duration from the Start date of the earliest starting task to the Finish date of the latest finishing task. The value of 60 days is correct, based on the data shown in your screenshot. It appears you have not yet set dependencies between the tasks, so the Duration of the summary task is the Duration of the longest subtask, which is the 2. Report builder task. 60 days = 12 weeks. Hope this helps.