Understanding Activity Duration Estimation in Project Management

In order to get a project started, aspiring project managers must learn how to perform a variety of tasks, one of which is estimating activity duration. Estimating project duration is not always an easy task because it requires a Project Manager’s knowledge of some theory as well as the application of some best practices and methodologies.

Estimating activity duration is a time-consuming process for a long-term project. Ideally, you should estimate the duration with your core project team. To reach an agreement on milestone dates and delivery schedules, you should involve the project team, who will work on the project to achieve the project objectives, the project management team, and all identified key stakeholders. You can create a project schedule with milestones based on this duration.

Estimating activity duration is iterative in nature and can be done for a project phase or a production phase. It can be changed as the project progresses and new activities are identified. You can begin by estimating your project based on the network diagram (sequencing the activities). It can be modified further based on changes made in the project during execution, controlling, and monitoring the process.

For estimating duration, the PMI® recommends a few project management tools, methodologies, and best practices. These are their names:

Estimation by analogy

This is a critical methodology that provides you with an estimate of the total duration. You can get a rough estimate of the overall duration based on information from similar previous projects. This information may be obtained from the Project Management Office or another project manager; you can use this template for your current project.

Analogous estimating the duration of an activity is less accurate in nature, but it is less expensive and time-consuming than other methods. When you don’t have enough time to do a proper estimate and you have a deadline, you can frequently use this method. Because you don’t have to estimate the entire project, analogous estimating can be applied to a portion of it. If the requirement/nature of the phase is very similar to the previous processed project, you can estimate activity duration for a single phase of the project.

Estimation Using Parameters

This method is more precise in its nature. It is based on a statistical analysis of historical data as well as other variables. In the case of a construction project, for example, you may already have the activity duration: cutting 1,000 stones will take 8 hours, and so on. If your project is similar to one that has been completed in the past, it is worthwhile to locate existing activity duration estimates and historical data from the previous project.

Estimation in Three Dimensions

This type of estimate takes into account various factors such as resource allocation, uncertainty, and risk—for example, best scenario-based and worst-case scenario-based estimates. The PERT concept gave rise to the three-point estimating concept (Program Evaluation and Review Technique). PERT is used to estimate three types of duration:

Almost certainly (M)

Positivity (O)

Negative in outlook (P)

Most Likely (M) is determined by the resources available, while Optimistic (O) is determined by the best scenario-based analysis. The final one, Pessimistic (P), is based on the worst-case scenario-based analysis. Once you’ve got these, you can use some very handy formulas to calculate the expected duration. These are their names:

Estimating activity duration is a time-consuming process for any long-term project. Estimating the project duration is a difficult task. Continue reading to learn more.

6 TE = (O + 4M + P)

TE stands for expected time, and O, M, and P stand for optimistic, most likely, and pessimistic durations, respectively. As a result, you can appreciate the significance of PERT in estimating the duration of your project.

Using Heuristic Estimation

This is also referred to as the Rule of Thumb. You can roughly estimate that the entire design phase will consume 45 percent of your total project time, and so on… This is a very useful technique for known phases where you can put an imaginary figure based on previous experience.

Analysis of Reserves

A type of contingency reserve is reserve analysis. After determining a schedule for each activity level based on the activity attributes, you can create contingency reserve timing by incorporating a percentage into the derived schedule for each activity. It can be changed as the work progresses, either decreasing or increasing depending on the circumstances.


Estimating the duration of a project—or its various phases—can assist you in successfully managing a project that is completed on time and within budget. Learn from the lessons your organization has already learned to save time when estimating activity duration. SPOTO Learning online Project Management training courses, including PMP Certification, can help you learn more about successfully managing projects of all sizes.

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