Realistic project estimates using PERT Program Evaluation and Review Technique

I have had several experiences with different managers with respect to estimates.
Some have said this is too high, some have said this is too low, please add lots of buffer. Some took my estimates and doubled it and gave it to their management. :)

So looking at PMBOK is there a good way to arrive at an estimate, yes one of the ways is to use the PERT estimation.

Break down you entire task in to activities and for each activity do the following.

The most pessimistic (P) estimate when everything goes wrong
The most optimistic (O) estimate where everything goes right (past experience doing similar projects can help here)
The most likely (M) estimate given normal problems and opportunities


PERT estimate for an activity = (O + 4M + P)/6

This is also called the weighted average. (Because the most likely estimate is weighed 4 times the other two).

Next time you are asked for an estimate try this & best of all after your activity is completed, try how realistic your estimates were !