# How To Estimate Activity Durations For Projects

### How To Estimate Activity Durations For Projects

Estimate activity duration is the process of estimating the number of work periods needed to complete individual activities with estimated resources. The key benefits of this process are that it provides the amount of time each activity will take to complete. Also, note that the activity is performed throughout the entire project. In this article, I want to look at how to estimate activity durations for projects.

Estimating activity durations use information from the scope of work, requires resources types or skills levels, estimated resource quantities, and resource calendar. Other factors that may influence the duration estimates include constraints imposed on the duration, efforts involved, or type of resources.

The inputs for the estimates of duration originates from the person or group on the project team who is most familiar with the nature of the work in the specific activity. The duration estimate is progressively elaborated and the process considers the quality and affordability of the input data.

For example, as more detailed and precise data are available about the project engineering work, the accuracy and quality of the duration estimate improve.

The estimate activity durations for projects requires an estimation of the amount of work effort required to complete the activity and the number of available resources estimated to complete the activity. These estimates are used to approximate the number of work periods needed to complete the activity using the appropriate project and resources calendars.

In many cases, the number of resources that are expected to be available to accomplish an activity, along with the skill proficiency of these resources, may determine the activity’s duration, but this is not a simple “straight line” or linear relationship.

Sometimes, the intrinsic nature of the work, that is, the constraints imposed on the duration, effort involved or the number of resources will take a pre-determined amount of time to complete regardless of the resource allocation.

### #1 Law of diminishing returns

When one factor such as resource used to determine the effort required to produce a unit of work increased while all other factors remain fixed, a point will eventually be reached at which additions of that one-factor start to yield progressively smaller or diminishing increase in output.

### #2 Number of resources

Increasing the number of resources to twice the original number of the resources does not always reduce the time by half, as it may increase extra duration due to risk, and at some point adding too many resources to the activity may increase duration due to knowledge transfer, learning curve, additional coordination, and other factors involved.

This may also play an important part and role in determining duration estimates for projects. For example, an increase in the output of a manufacturing plant may be achieved by procuring the latest advances in technology, which may impact duration and resource needs.

### #4 Staff motivation

The Project manager also needs to be aware of Student syndrome-or procrastination-when people start to apply themselves only at the last possible moment before the deadline, and Parkinson’s law where work expands to fill the time available for its completion.

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