By default, Primavera P6 summarizes/rolls up activity duration at the WBS level by calculating the period from the earliest Start Date to the latest Finish Date of all activities in that WBS. In case we want to calculate the summary duration by simply adding up the duration of all activities, below are the steps.
Go to menu Enterprise -> User Defined Fields.
Create a new Field (e.g., “TotalDuration(SimplyPlus)“) with Data Type “Integer”.
Go to menu Tools -> Global Change.
Create a new Global Change (e.g., “AssignValueToTotalDuration(SimplyPlus)“). The formula is as the following picture.
Run the new Global Change.
Now, besides the default summary duration, we can also see the new summary duration calculated by simply adding up the duration of all activities.