Data Type Duration
Entry Type Calculated or entered
Description The Expected Duration field contains the total span of active working time expected for a task, that is, the amount of time from the expected start to expected finish of a task. You can enter the expected duration as part of a PERT analysis calculation, which takes a weighted average of expected, pessimistic, and optimistic dates and durations, or you can have Microsoft Office Project calculate it for you. This field is available only in the PA_Expected Case table or the PA_Expected Gantt view.
How Calculated When you first create a task, the Expected Duration field contains "0 days." When you enter expected start and finish dates, and then click Calculate PERT 
Best Uses Use the Expected Duration field in the PA_Expected Case table or the PA_Expected Gantt view to estimate the probabilities of task dates. By default, the PERT analysis calculation gives the heaviest weight (4) to the expected information, and the lightest weight (1 each) to the pessimistic and optimistic information.
Example You have several critical tasks for which you want to see the best-case, worst-case, and expected durations. You enter the expected start and finish dates for these tasks, as well as their optimistic and pessimistic start and finish dates, and then run the PERT analysis calculation.
Remarks By changing the weight that Project attributes to each of the three estimated durations, you can tailor the probable estimate to be more accurate. To change the weight, click PERT Weights 
The Expected Duration field uses the Duration2 custom duration field.
