Understanding the Estimation of Activity Duration in Project Management

Pursuing project managers must understand how to perform various tasks to get a project started, and estimation of activity duration is one among them.

It isn't always a seamless activity to estimate project duration, as doing so requires a project manager's knowledge of a few theories, along with applying a few top techniques and practices.

Estimating activity duration is a daunting procedure that takes time for a long-term project. Ideally, it would be best to involve your core team in the estimation process.

It would help if you involved them, who will work on the project to attain the goal, the project management team, and all identified stakeholders to make a consensus on the target dates, and delivery schedules.

Estimating activity duration can be transformed as work progresses and as new activities of the projects are identified. Firstly, you can evaluate your project depending on the network diagram and can be further changed based on project changes done during the execution, controlling, and monitoring of the process.

According to the Project Management Institute (PMI), there are some project management practices, techniques, and tools to estimate the activity duration, and they are as follows:

Parametric Estimating

Parametric Estimating is more precise and is based on a statistical calculation of historical data and other variables. For instance, in the design stage of a construction project, you may already have the activity duration, i.e., cutting 1,000 stones will take 8 hours.

If your project is similar to one executed before, it's worth your while to determine existing activity duration estimates and previous data from the past project.

Heuristic Estimating

Heuristic Estimating is called Rule of Thumb, where you can roughly guess that the whole design stage can take 45% off your entire project time. This is a fruitful method for knowing factors where you can place an imaginary figure depending on the experience.

Analogous Estimating

Analogous Estimating is a vital technique that offers you the whole duration estimation. Depending on similar projects, you can attain a ballpark view of the entire duration estimation.

You can also get this data from the Project Management Office or other project managers and use this template for your existing project. Though this estimation practice isn't so precise in nature; however, it's less expensive and less time-consuming than other techniques.

You can often leverage Analogous Estimating when you don't have enough time to undergo a proper estimation and have a timeline. This can be a part of the project, so you don't need to estimate the whole project.

You can estimate the activity duration for a single stage if the phase requirement is identical to the last processed project.

Three-point Estimating

Three-point estimating depends on considering several choices such as resource assignments, uncertainty, and the associated risk like the best and worst scenario-based. This estimating technique originated from PERT, and through PERT, we estimate three kinds of estimation:

1. Most Likely (M)
2. Optimistic (O)
3. Pessimistic (P)

Most Likely is based on the resources assigned, Optimistic is based on the best scenario-based analysis, and Pessimistic is based on the worst scenario-based analysis. Once you have these three durations, you can leverage some valuable formulas to derive the expected duration, i.e.,

TE = (O + 4M + P) ÷ 6

Where, TE = expected time

In this way, you can understand the significance of PERT in estimating the duration of the project.

Reserve Analysis

This is a type of contingency reserve, where after fixing a schedule for each activity level based on the activity features, you can create reserve timing by adding a few percent to the derived program of each activity. It can be modified as work progresses, minimizing or maximizing depending on the scenario.

Final Call

Estimating project activity duration can help you manage the project that comes in on time and within budget. Understand from the lessons your company has already dissolved to save yourself time when doing duration estimates.

To learn more about successful project management, look to iCert Global's online PMP certification training course.