Traditional PERT techniques use a formula for
calculating estimated activity duration. The project
manager first determines three time estimates for each
activity:
Optimistic time (O) – generally the shortest time in
which the activity can be completed.
Most likely time (M) – the completion time having the
highest probability.
Pessimistic estimate (P) – the longest time that an
activity might require.
The expected activity duration is then calculated as :
expected time = (O + 4M + P) / 6