The process of estimating the number of work periods that are required to complete activities using an estimated amount of resources is defined as estimate activity duration. It is important in project management for project managers to determine the work periods necessary to complete individual tasks and processes.

It can be based on historical information as well as making construction estimates. There are three types of estimate duration and these include the optimistic, most likely and pessimistic duration. The most likely duration is an estimate of the most probable duration of a particular activity. This type of duration takes into the account all the known variables that may affect the performance of the entire project.

There are many factors that affect the most likely duration and these include the historical information of a previous yet similar project. Project managers may also need to use the resource requirements and capabilities of a particular project management activity. It can also be used to modify the constraints and assumptions from the other processes while planning the project. Lastly, looking at the time reserve is also important in determining the most likely duration of the project.