What I Wish I Knew About Estimating Activity Durations in Agile Projects

estimating project activity durations

Before creating a project schedule, you must understand estimating activity durations. Without the knowledge or relevant data, the project schedule will play blind.

To make accurate predictions and a precise project schedule, you must utilize all the tools and techniques at hand, and estimating activity durations is one such technique that can take you closer to your goal.

Task Completion and Time Estimates

A slight miscalculation can throw the whole project off track. In contrast, accurate estimation of activity durations can help you create an accurate plan schedule and help in cost estimations.

Activity duration estimation, however, is not an easy task. Considering the minute details of a project and the tasks included, there are plenty of details to consider before predicting activity durations, such as start and end dates, budget constraints, resources required, etc.

To start on the right foot, PMs use available tools and techniques of which estimating activity durations is a part. To better understand the process and how it can help you, we have come up with this post that will provide in-depth knowledge of the process and everything you need to know about it.

Let’s dive right in!

What Is Activity Duration Estimation?

Activity duration estimation, simply put, is the amount of time required to complete an activity. It is a process by which PMs gather all the information they need and estimate the duration of each activity in the project management process.

These estimations can span months or hours, depending on the activity. The estimations have an overarching benefit: they help PMs calculate the estimated time of project delivery and the project schedule.

Since project schedules are essentially a breakdown of the project into smaller chunks, correct time estimation of each activity’s completion can help PMs create a more efficient project schedule. The estimation process requires input from the individuals involved in the project and other techniques that can help project accurate estimates.

Before we move on to the techniques used for estimating activity durations, let’s look at the inputs required for the process.

Inputs For Estimating Activity Durations:

Here is a list of some of the inputs that can help make accurate estimations:

  • Activity List: A list of all the activities to be performed in the project.
  • Constraints: Any factors that can (positively or negatively) influence a project’s progress.
  • Resources Required: The number of resources required to accomplish the activity.
  • The capability of the Resources Involved: The capability of the resources to accomplish the activity, whether they can successfully complete the assigned task.
  • Historical Data: Data from previous projects can serve as a guiding light for estimating durations for similar activities.
  • Potential Risks: Risk factors involved in the project and how they can affect the project’s progress. 
  • Resource Availability: Whether the resources required for the project are available in the required time period.

With the right information and inputs, you can now move on to the tools and techniques for estimating the durations of different activities that suit you best. Fortunately, you have multiple options to choose from, so feel free to read through and choose the method of your choice.

Tools And Techniques for Estimating Activity Durations:

Here is a list of tools and techniques you can use to estimate the time durations of activities in your project accurately:

1. Expert Judgement:

Expert Judgement, as the name suggests, relies on the judgment of an expert to estimate activity durations. Expert opinion stems from experience and skills, so decisions guided by them are more often than not fruitful.

Experts in question are people with extensive knowledge and experience in the field and are very familiar with the estimation process. Expert judgment is a simple yet efficient way of making accurate estimations.

2. Analogous Estimation:

The next technique for activity duration estimation is an analogous estimation. The technique, also known as top-down estimation, utilizes data from previous similar experiences to carve out the details of the activity and predict estimates. It also involves the opinion of experts and their past experiences.             

The activities included in the project are compared with similar activities from past projects as an analogy to identify how long the current activity will take.

Analogous estimating works best when you do not have sufficient information about the details of the activity. The accuracy of the estimations depends on the similarity of the past and present activities as well as the success rate of the activity. The technique is less costly and more time-efficient than others on this list.

For analogous estimation of an activity, for example, you will search for a similar activity in past projects. T

hen, utilize the data obtained from that source, ask for an expert’s opinion, and then estimate the duration of the activity.

3. Parametric Estimation:

The parametric estimation uses a mix of historical data as well as statistical calculations to make more accurate estimations. The technique comes in handy if you have sufficient data and you make accurate statistical calculations.

For example, if a past task similar to the current task took 5 resources and 5 days to complete, how many resources will it take if the time duration is halved? Historical data and calculations help predict more accurate durations. This technique is more reliable than the ones mentioned above.

4. Bottom-up Estimation:

Bottom-up estimation is the next technique on our list. In this technique, PMs take a bottom-up approach. Activities are broken down into smaller parts, and the duration is estimated for each part. The cumulative duration of smaller procedures within the activity gives the duration of the activity.

This technique is more precise since it dives deep into the details of the activity but is also time-consuming and demands attention and effort. That said, the results obtained are more accurate and fruitful.

5. Reserve Analysis:

Reserve analysis estimations come in handy in case of risks and issues hindering projects’ progress. It involves the addition of a contingency duration that acts as a buffer in case of risks. The time reserved for contingency can be a fixed duration added to each activity or different depending on each activity.

The time added can be increased, decreased, or removed with the project’s progress. The availability of reserves gives teams ample time to get rid of the risk without affecting the actual schedule of the project.

6. Three-Point Estimation:

Three-point estimation is perhaps the most renowned estimation technique of all. As the name indicates, three-point estimates require estimating three different durations. These estimations consider various factors to make the most accurate estimations.

The three estimates are:

  • Most likely: The activity duration estimation is the most realistic and likely to happen. This is an average estimation and is common in most cases.
  • Optimistic: Optimistic estimations are based on the best-case scenario. These estimations are ideal durations when everything goes as planned and assumes favorable conditions.
  • Pessimistic: Pessimistic durations are the ones based on the worst-case scenario. These estimations assume everything that can go wrong and then calculate durations on that assumption.

All these estimates provide an upper limit and lower limit for the duration. A formula is then used to derive the expected activity duration. The formula is:

Te = (To + Tm + Tp) / 3

  • Te is the estimated time
  • To is the optimistic time
  • Tm is the most likely time
  • Tp is the pessimistic time

PERT chart, however, is the most commonly used three-point estimation technique, and the formula used there is:

Te = (To + 4Tm + Tp) / 6

7. Group Decision-Making:

Group decision-making is another technique similar to the expert judgment technique. This technique makes decisions after consulting group members and discussing the details with them. Since these estimations are based on the opinions of the resources involved, they are more likely to reap good results.

PMs can consult team members for their opinion, draw from their experience and then make relevant estimations.

Process of Activity Duration Estimation:

Let us take a look at the steps involved in the process of activity duration estimation:

  1. Identify and define the activities included in the project. Work breakdown structure (WBS) can help divide the project into smaller chunks of activities it involves.
  2. Next is organizing the activities correctly and identifying the relationship between different tasks.
  3. The third step of the process is the most important. Using the abovementioned techniques, calculate the time duration required to accomplish an activity.
  4. Ask for experts’ judgment and your team’s opinion, and use the historical data for precise calculations. Also, add reserves in case of potential risks.
  5. The next step is the development of a schedule with all the details, including start and end dates, sequence, resources, etc.
  6. Lastly, PMs must be on the lookout for potential roadblocks or opportunities and make timely adjustments to make the most of them.

How Are Activity Duration Estimations Beneficial in Project Management?

For project managers, creating a near-perfect project schedule is necessary to make sure that the project will be completed within the stipulated time and will produce good results. Following is a list of benefits that come with activity duration estimation:

  • Activity duration estimations can help project managers create project schedules. With each activity and time duration calculated beforehand, creating and organizing a project schedule becomes much easier.
  • Duration estimations help PMs assess the amount of time required to complete the whole project successfully. They can then make relevant changes in resources schedule and activities to ensure the project follows that timeline and is completed on time.
  • The duration of an activity can help PMs analyze whether or not the project is progressing smoothly. If an activity deviates from the time estimation, then PMs can take remedial measures to control the situation.
  • Activity duration also comes in handy when calculating the capabilities of resources. With the data in sight, PMs can take additional onboard resources to ensure the activity is completed within the predicted time.
  • Cost estimation is another key benefit of the process. Time estimation not only helps with creating timelines but is also helpful in calculating the costs of the activities and the project.
  • Since cost estimation, more often than not, requires input from experts and team members. As such, it can improve communication and collaboration, which ultimately contributes to the productivity and efficiency of the team.

Signing Off:

We hope this article has helped you understand all the details of Estimating Activity Durations. This was all from our side. If you have any queries, you can contact us via email, and we will get back to you as soon as possible.

Till next time, goodbye and good luck!


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