Project Management

Deep Dive: Project Schedule Management: Estimate Activity Durations

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Categories: estimating

Last time in the deep dive into the PMBOK Guide®-- Sixth Edition I looked at Project Schedule Management and the Sequence Activities process. You’d expect today’s instalment to be covering Estimate Activity Resources, which is what came next in the PMBOK Guide® -- Fifth Edition.

However, that process has now moved to the Resource Management Knowledge Area so we skip ahead to Estimate Activity Durations.

Estimate Activity Durations Process

This is (now) the fourth process in the Knowledge Area. We’re still in the Planning process group.

The point of this process is to work out how long each activity is going to take. You’ve already got the tasks in a logical sequence. Next it’s time to work out the overall duration of the project based on the duration of the individual tasks.

The main output is a set of estimates. These feed into the next process, where you create a project schedule.

In my experience, building the schedule and working out the activity estimates are two processes that overlap majorly. I’ll start creating the schedule in my project management software from the task list, and update the task information with durations as and when I know them. So the schedule is developed as each estimate (and other information like resource availability) is added.

Go into this process knowing how the estimates are going to be used, and you might save yourself some time when it comes to adding them into your schedule. This is all about being effective and managing your planning in an integrated way.

Right. Let’s look at the detail of this process starting with the Inputs.


There are quite a few changes to the Inputs between the PMBOK Guide® -- Fifth Edition and Sixth Editions. Mainly, it’s items being removed. We’ve lost eight specific documents and replaced them with the generic Project Management Plan and Project documents.

This is a trend in the new edition. It’s a good trend too, as it allows us to be more flexible with the Inputs and use the paperwork that is most relevant to the project.

The important parts of the project management plan are the schedule management plan (as this includes some background info on expected level of accuracy and possibly other criteria useful for starting out estimating) and the scope baseline (as the WBS dictionary may include some criteria that would affect the estimate e.g. technical details or constraints).

Useful project documents to refer to during estimating include:

  • Anything that describes the tasks, so activity attributes and the activity list or WBS
  • The risk register, in case it has anything of value to consider when estimating
  • The lessons learned register, for the same reason
  • The assumptions log, as you may have to revise or update assumptions, or take them into account when estimating.
  • Information about the team, because the person doing the task affects how long the task will take – an experienced resource will be faster at completing work than someone new.

Tools & Techniques

Group decision making techniques and reserve analysis have dropped off the Tools and Techniques list.

Instead, we’ve got bottom up estimating (I’m not sure why that wasn’t on there before, as other types of estimating were – looks like an oversight to me), data analysis (broader than reserve analysis) and meetings (which you can argue includes making decisions as a group).

Most of the Tools and Techniques unsurprisingly relate to estimating approaches. As the main output is your estimates for task durations, you need to know how to estimate and which is the best estimating approach to use at any given time.

I’ve written quite a lot about estimating techniques in the past. Here are some articles to take these T&T further:

Analogous estimating

Parametric estimating

Bottom up estimating

And at some point I’ll get round to writing about three point estimating – that’s actually a technique I use and I consider it to be one of the better ways to estimate knowledge work.


Activity duration estimates have been renamed ‘duration estimates’. These are statements about how long a task will take, either as a range, a defined number or similar.

There’s a new output for the basis of estimates, which is really important. If you haven’t been clear about how you created the estimate, you can’t explain the basis on which you reached the numbers. This is essential for helping other people understand the boundaries of the estimate, its reliability and whether or not it’s a final position. The basis of estimates should include an indication of the range used and confidence levels and can also refer to any risks that would influence the likely accuracy of the estimate.

Project document updates stays the same – you will have to update a range of paperwork, depending on what changes or needs review as a result of your estimates.

Next time I’ll be looking at Develop Schedule.

Pin for later reading:

Posted on: March 12, 2019 09:00 AM | Permalink

Comments (13)

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Fantastic, looking forward to the next one, thanks for sharing!

Glad you are finding it helpful

Fantastic!!!. Thanks for Sharing.

Nice comparison between 5th and 6th edition. Really helpful to understand change in current edition.

Thanks for sharing !!

Thank you Elizabeth! Very well summarized article..

Well organized summary with comparison between 5th and 6th editions. Thank you for sharing Elizabeth

Great summary, as always!

Good information again. Thank you.

Thank you for sharing this article.

Well written concise summarisation. Awaiting eagerly for the next post

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