Estimate Activity Durations – Important Process For Developing Schedule

Estimate activity duration process is all about estimating the duration for each activity in the project. The estimate activity duration process is an important process before developing the project schedule.

You might have already observed we are talking about duration and not the effort.

What is the difference between duration and effort?

Duration is the lead time for completing an activity. This is dependent on many parameters. For example, some parameters are such as

  • How much amount of work is associated with an activity
  • How many resources are working on this activity.
  • Skill and experience level of the resources working on the project, etc.

On the other hand effort is the total time (number of hours/days/weeks/months/years)  that is going to be spent on an activity.

In the estimate activity durations process, we will focus on estimating the duration of an activity.

Estimate Activity Durations

When Estimating Activity Durations Process Is Performed?

This is completely dependent on what inputs are primarily required for the estimate activity durations process.

Estimate activity durations process is primarily dependent on estimate activity resources process for the activity resource estimates as the primary input for estimating the activity durations.

And you also remember that estimate activity resource process is dependent on the define activities process for the activity list in the project.

So estimate activity durations process needs to be performed after you define the activities and you estimate activity resources for the project.

Estimate Activity Durations Process ITTOs

The primary objective of this process is to come up with duration estimates for each activity, so that the activity durations can be used as an input to develop the schedule.

The following are the ITTOs for the estimate activity durations process.

Inputs Tools & Techniques Outputs
  • Schedule management plan
  • Activity List
  • Activity Attributes
  • Resource Calendars
  • Activity Resource Requirements
  • Project Scope Statement
  • Risk Register
  • Resource Breakdown Structure
  • Enterprise environmental factors
  • Organizational process assets
  • Expert Judgement
  • Analogous estimating
  • Parametric estimating
  • Three point Estimating
  • Group Decision Making Techniques
  • Reserve Analysis
  • Activity Duration Estimates
  • Project Document Updates


Schedule management plan

Schedule management plan will describe the approach of how the other processes of time management knowledge are should perform.

In this case schedule management plan will provide methods of how to estimate activity durations and what is the level of accuracy of these estimates.

Activity List

Activity list is the complete list of activities in the project. To estimate the durations for each activity in the project, you would need activity list as the input to this process.

Activity Attributes

Activity attributes are additional information about the activity. So whenever you use activity, you would also need to activity attributes to understand more about the activity. For example activity attributes can be the predecessor, successor, assumptions and any constraints on that activity, etc.

Resource Calendars

We have seen resource calendars are handy to understand the resource availability as well as to tag any resources for the activities in advance. So resource calendars show the usage of resources in the current project and other projects of the enterprise.

Activity Resource Requirements

Eventually activity resource requirements are an output of the estimate activity resources process. And this is one of the primary inputs in the estimate activity durations process.

Project Scope Statement

Project scope statement may have important assumptions and constraints which may impact the duration of an activity. Hence project scope statement is an input to estimate activity durations process.

Risk Register

Risk register contains all the risks that are identified in the project to that point in time.  As part of the estimate activity durations process, you would need to revisit to see the impact of the risks on the activity durations.

Resource Breakdown Structure (RBS)

Resource breakdown structure is hierarchical representation of resources based on the type and category of resources.

Enterprise Environmental Factors

Enterprise environmental factors are part of common ITTO s for many project management processes. Please read the blog post on common ITTO s for more details.

In this context, your organization might have ways of working or practices on how to perform an activity. For example, to replace a laptop, organization may have process which will take more time. This may impact the activity duration.

Organizational process assets

Organizational process assets are a common ITTO s for many project management processes. Please read the blog post on common ITTO s for more details.

In the estimate activity durations process, you can refer to the estimate activity durations process in the similar historical projects. Also lessons from historical projects are also help in this process.

Tools & Techniques

Expert Judgement

Taking expert or SME opinion, who did the similar activity in the past will help in the estimate activity durations process. Expert judgement is again a common ITTO. Please read through blog post on common ITTO s for more details.

Analogous Estimating

Analogous estimating is about taking the estimate of a similar activity in another project for estimating duration of an activity in the current project. So the duration for the similar activity in the historical projects is used as the duration of the similar activity in the current project.

Parametric estimating

Sometimes you have an equation or formula with parameters listed. And you input the parameters that will estimate the duration for the activity. So this could be a tool, or excel sheet or small piece of software.

For example you have spreadsheet that calculates the duration based on the total number of resources and the total effort, then this is called parametric estimating.

Three point Estimating

When you have historical information as a basis for the activity duration, you can approach by taking a single point estimation. However when you are doing the estimation for the first time it is always better to use a three point estimating. There are primarily two ways of calculating three point estimating. They are

  • Beta distribution or program evolution and review technique (PERT).
  • Triangle distribution

Please read through the blog post on three point estimating and PERT for more details on this.

Group Decision Making Techniques

Approaching the team with discussions to determine the best duration for an activity.

Reserve Analysis

Eventually reserve analysis is about adding reserves or buffers in the activity durations to account the uncertainties in the activity.

Actually adding buffers in the activity is not a good practice. But when you have uncertainties, you consider the reserves for the activities.

However the project manager keep on monitoring the risks and as and when more information is available on these risks, accordingly the reserves will come down or go up in each of the activities.


Activity Duration Estimates

Indeed this is the primary output of the process estimate activity durations. This describe the duration required to complete the activity.

Project Document Updates

Project Document Updates is a common ITTO for many PMP processes. Please read through the blog post on Common ITTO s for more details.

Indeed the estimating activity durations, you may see updating the activity list, activity attributes to name a few. So activity list and attributes may update with more information about the activity, if any. For example you may need to update the assumptions pertaining to an activity.


To conclude with, we started with what the estimate activity durations process is all about.  Then we have seen when to perform the estimate activity durations process.

Finally we have seen the ITTOs pertaining to estimate activity durations process.

If you see the order, we have

Finally it is time to develop the schedule using all this information that we have from the above processes.

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