Effort and duration: key differences in the estimate of project

differences among effort and duration

Time management is one of the most important aspects in managing a project.

In order to estimate the time accurately, it is necessary to have a correct understanding of the two concepts of effort and duration.

What is effort

Effort is the number of units of work needed to complete a task.

It is usually expressed in hours, days or weeks worked.

Therefore, it calculates the number of hours of work needed to complete a task, i.e. the actual time spent working on the project.

In order to estimate the duration of a project, first we have to determine the effort.

Let’s make an example to simplify the concept: if you estimate about 30 hours of active work to complete a fence, the effort will be 30 hours.

Be careful, however, that this does not mean that the fence is ready within 30 hours – unless you plan to build it for 30 hours non-stop.

The duration is the total number of work periods (excluding holidays or other non-working periods) necessary to complete an activity, so in other words it is the total time needed to complete an activity.


The duration is usually expressed as working days or working weeks and depends on the availability and capacity of the resources.

For example, if you spend 3 hours a day working on the fence, the total duration would be 10 days (30 hours of total effort divided by 3 hours / day).

But if, for example, a friend helps every day, then you would have two resources working for 3 hours a day on the fence = 6 hours a day.

The duration in this case would therefore be 5 days (30 hours of total effort divided by 6 hours / day).

However, if the friend could only work 2 hours a day, the duration would extend to 6 days because the resources would only work for a total of 5 hours a day.

The total effort is always 30 hours, no matter if there is one, two or more people working on the project.

It is not possible to reduce the effort to 15 hours if two people work on the project, but it is possible to reduce the overall completion time.

The concept of Schedule Padding

The estimates represent one of the most critical and complex areas for a project manager.

It is never certain that these are correct and there is always the doubt that they may be mistaken for excess or defect, despite all the good will in formulating them.

The estimation techniques, such as the analogy or bottom-up estimations, can provide more or less reliable estimates, but all have the same problem: they depend on the capabilities of those who formulate them.

The concept of Schedule Padding means adding more time / value to the estimate, a sort of “pad” (hence the term Padding) that can soften the “fall” in case of unforeseen events or errors of evaluation.

When there is not enough information or experience to make a realistic estimate, it is very easy to fall into the “Padding” technique.

In other words, there is the tendency to increase, even exceedingly, the estimate of duration due to excessive prudence.

Clearly, if everyone in the company, including the project manager, uses this technique, the final estimate would be totally exaggerated and misunderstood.

So, how to avoid Schedule Padding?

In project management, it is advisable to first estimate the effort and after that duration.

The effort is the total estimated time for the realization of a task, of an activity. In other words, the total worklog dedicated to the activity.

The duration is instead the time interval required for the realization of the task / activity based on the availability of resources and the project calendar.

With respect to the 8 hours that correspond to the normal working day, the TenStep methodology considers productive only 6.5 hours.

This is also a value that should be kept in mind and that is not always considered during the scheduling of a project.

At Twproject, in our project management tools, we insert both project and routine activities, in order to have clear how much time each resource can really devote to its activities.

Start now with a correct scheduling

In Twproject you can insert every type of activity, from routine to projects, with work hours and unavailability.

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Techniques to avoid Schedule Padding

There are several possible techniques to decrease the risk of Schedule Padding:

  • Ask for the opinion of a disinterested professional regarding the project;
  • Use the PERT method (Program Evaluation and Review Technique), also known as a 3-Point estimate, which provides a more optimistic, a more pessimistic, and a more probable estimate.
  • Grant the time it takes for those who have to make the estimate without putting pressure or haste.
  • Add extra time to the overall project, and not to every single activity.
  • As previously mentioned, determine the effort first and only then the duration of the activities.

Not all collaborators have the same productivity and they do have different knowledge, skills and experience.

This is why the ability to make an estimate as well as the time needed to do it can vary.

Advice for a correct estimate of the effort

Everything starts from the estimation of the effort. So let’s see some tips to better identify it, subdiveded by category:

Basic effort estimates:

  • Estimating is an open activity and should happen regularly during the project. The initial estimate will thus be increasingly deepened and gradually perfected.
  • During the initial phase of a project, make sure that everyone agrees on what should be delivered and therefore estimated. Saying everyone, we mean the project manager and project team in the first place, but also executives and all project stakeholders.
  • Involve experienced people in the analysis and estimation process and brainstorm with the people who will actually have to do the job. It is useful to have different groups of people giving an estimate to the same thing. If comparing the results shows a large disparity between the numbers, it means that the uncertainty on that specific activity, or on the project in general, is high.

Estimates on the degree of contingency:

  • All estimates bring an intrinsic degree of uncertainty, especially in the early stages of the project in which there are more unknowns. It is essential to quantify the percentage of unknowns in the estimate and to compensate with an equivalent level of contingency.
  • It is important to always consider the project risks and contingencies; never make estimates only considering the best case.
  • Research and experiment with different tools and estimation techniques. The estimation tools will help you to consider all the different aspects of the project and will automatically add further contingency.
  • Estimate the effort in points or working hours with respect to the calendar time to cope with the fact that the team is never 100% effective. You can also apply a separate conversion factor to translate the estimated effort into calendar time. This will make it easier to track the accuracy of the estimates. If, for example, the team spends 30% of the time of an average day in meetings, answering the phone and email, an appropriate conversion factor must be added, in this case corresponding to 1.4 (1/70% ).

Overall estimates:

  • It is essential to take into account all the phases and activities of the project, including analysis, designing, planning, realization, eventual re-elaboration, delivery, project closedown.
  • Formally record estimates and document how they were elaborated, from which information and through which processes. It is important to make clear the purpose and the hypotheses estimated and highlight what is out of scope. This will not only put the project manager in a better position to defend numbers, but will also help to review and improve the estimation process in the future.

Bottom line

As explained, understanding the difference between effort and duration of an activity is therefore fundamental for the correct planning of a project.

In Twproject, it is possible to estimate how much work is needed to complete a task or close an issue.

These estimates are taken into account in the assessment of the workload, a very useful tool in this regard, which you can find on our platform.

Twproject takes into account the available hours of the resource, with the definition of the working hours in cross-reference with the schedule and unavailability.

The tool also allows you to enter routine projects that reduce the actual hours that resources can devote to projects, so you always have an up-to-date and more realistic load.

With Twproject you can also intervene in real time on assignments to rebalance them if needed.

What do you think about this topic? Do you want to try to improve the way you estimate projects and check the load of your resources?

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