Probably the most common action undertaken by project planners everywhere is assigning a duration to a task; most of us do this almost automatically. Generally it is only when a dispute arises that the complex interaction of the factors discussed involved in setting the duration come into play.

There is no universal answer to the question of what is the ‘correct’ way to assess durations but here is an overview of the multiple factors that should be considered by competent planners and managers.

Distributed contingencies are normal in most aspects of project management but often result in sub-optimal use of resources. Typical examples include allowing some safety margin in each CPM duration estimate (eg, setting the durations at an 80% probability), allowing contingencies on a project by project basis for risk, setting budgets with a 90% confidence limit, etc.