A milestone is an event on a schedule which marks the completion of key activities.
This could be the completion of a Work Package, a technical stage or a management stage.
In a commercial environment, reaching a milestone may be the trigger for a payment to a supplier.
Breaking the plan into intervals associated with a milestone allows the Project Manager to have an early indication of issues associated with the schedule itself, and also a better view of the activities whose completion is critical to the timeline of the plan.
While there is no ‘correct’ number of milestones or duration between them, they lose their value when there are too many or too few.
There should be far fewer milestones than deliverables or Work Packages, but there should be enough milestones at major intervals to gauge whether or not the plan is proceeding as expected.
PRINCE2® 2009 describes project monitoring within the Progress theme.
The purpose of the Progress theme is to establish mechanisms to monitor and compare actual achievements against those planned; provide a forecast for the project objectives and the project’s continued viability; and control any unacceptable deviations.
Two of the principles of PRINCE2 are managing by stages and continued business justification.
The Progress theme provides the mechanisms for monitoring and control, enabling the critical assessment of ongoing viability.
[see Progress - Purpose]
PRINCE2® is a Registered Trade Mark of the Office of Government Commerce in the United Kingdom and other countries.