How do you Determine Activity Duration, and Can ChatGPT Help you?

Determining the duration of activities is an important step in developing a realistic and reliable baseline schedule for any construction project. Getting this right from the start sets the tone for accurate planning, progress tracking, and successful project delivery. While many factors influence how long an activity should take, there are four primary techniques commonly used by planning engineers and schedulers to estimate durations effectively. In this article, we will explore these four techniques, explain how each one works, and discuss when it’s best to apply them in the planning process.

Duration Estimation Techniques

The purpose of estimating activity duration is to determine the amount of time it takes to complete an activity.

Example.

The duration of the activity “Formwork for Foundations” is 7 days. Starting from 10-Apr.-2025 to 17-Apr.-2025

This duration affects the schedule because after finishing the 7 days, another activity shall start. If this activity is on the critical path, then this activity is affecting the project’s finish date.

If you want to learn more about the critical path, you can check this article: “How many critical paths we might have in one construction project”

So, how did we know that this activity required 7 days to be finished?

The Four Duration Estimation Techniques

1. Analogous Estimation

2. Parametric Estimation

3. Three-point Estimation

4. Bottom-Up Estimation

1.    Analogous Estimation

Analogous estimating is a technique that involves using either historical data or the experience of estimators to determine the expected duration of an activity.

Example:

If we have an old project where the pouring for 150 m3 of concrete took 3 days. We can use this as an equation to determine the duration for the new project

Duration= (250*3)/150= 5 Days

We can avoid this formula with the presence of an experienced planner or estimator.

Example:

The estimator or planner knows the average time required to pour concrete and the capacity of the equipment that will be used because they have been working in this field for several years; this helps them in providing reliable information.

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2.    Parametric Estimation

Parametric estimating uses an algorithm to calculate cost or duration based on historical data and project parameters. This case includes more factors in making the decision on the activity’s duration.

Example:

In the past project, we poured 150 m3 in 3 days, but now we have less experienced labors, so the estimation for pouring the 150 m3 will be 5 days.

3.    Three-Point Estimation

Multipoint estimating assesses duration by applying an average or weighted average of optimistic, pessimistic, and most likely estimates when there is uncertainty with the individual activity estimates.

We have two methods in this technique, Triangular Distribution and Beta Distribution, but what is the difference?

O: Optimistic

M: Most Likely

P: Pessimistic

Example:

O: 7 Days             O: Optimistic

M: 10 Days          M: Most Likely

P: 15 Days           P: Pessimistic

4.    Bottom-Up Estimation

​According to the Project Management Institute (PMI), bottom-up estimating is defined as:

“A method of estimating the duration, cost, or required resources by aggregating the estimates of the lower-level components of the work breakdown structure.”

In the context of construction management, this technique involves breaking down the project into work packages. Each of these components is individually assessed to estimate the necessary resources, time, and costs. These detailed estimates are then aggregated to form a comprehensive estimate for the entire project. This approach enhances accuracy in project planning by providing detailed information from the lowest levels of the work breakdown structure.

Example:

If we have an activity called “Ground Floor Slab” and we want to calculate the duration it will take to finish this activity. in this technique we will break down the activity to steps of the actual work that needs to be done and refer to any of the techniques mentioned above to know the duration of each step and sum them all to know the duration.

Formwork: 3 Days

Steel Fixing: 5 Days

Pouring Concrete: 1 day

So, the total duration of the activity = 3+5+1=9 Days

Can ChatGPT Help in Estimating the Duration of an Activity

When estimating the duration of an activity in Primavera P6, planners typically rely on historical data, expert judgment, or standardized techniques like bottom-up estimation. However, with advancements in technology, Artificial Intelligence (AI) tools, such as ChatGPT, have become valuable assistants in this process. Instead of conducting time-consuming manual research or calculations, planners can now ask AI to suggest realistic durations based on similar past projects, industry norms, or customized parameters. This not only speeds up the estimating process but also enhances accuracy and consistency, especially in the early planning stages where data may still be limited. Integrating AI support into duration estimation can streamline the workflow and empower planners to make more informed decisions with greater confidence.

Example:

Conclusion

Estimating activity durations accurately is the basis of building a reliable baseline schedule in Primavera P6. Whether you rely on expert judgment, historical data, parametric techniques, or bottom-up estimation, each method brings unique strengths depending on the nature and complexity of the project. The integration of AI tools—like ChatGPT—has added a new layer of efficiency by allowing planners to generate quick, data-backed duration estimates, cross-check productivity rates, and simulate real-world scenarios in seconds. While AI should complement—not replace—human experience and site-specific knowledge, its growing role in construction planning is undeniable.

You can enroll in our Construction Project Planning Intermediate Level with P6 Course to learn more about techniques and construction management concepts.

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