Effort and duration: difference and priority


Estimating project effort and duration is a core element of any project planning.

The goal of effective project management is to complete the project on schedule. The accuracy of the overall project program therefore depends on the precision of the effort and duration estimates.

What is effort?

In simple terms, effort is simply the amount of hours that workers spend, focused on a particular task, to achieve a particular result.

Effort is often expressed in hours, days or weeks spent by workers.

Stakeholders often want to know how much a project will cost. This mainly depends on how much time the project members spend on the project.

So here is a simple example to explain this concept:

To paint a house you need 6 hours a day of work for 9 days.  The effort  is therefore the amount of time you spend in a day multiplied by the number of days of work required, in this case 54 hours. The effort is therefore 54 hours.

Not just Effort but also time factor

Time is a unique, non-renewable and irreplaceable resource. Time estimation and management can therefore create or destroy a project. It is essential that the project manager knows how to approach them.

It is also important to estimate the time correctly, for two main reasons:

  • Project planning and delivery deadlines are based on estimated project duration. An inadequate estimate translates into delivery times that go beyond the expected timescales and may not only affect the company’s financial performance, but may also raise doubts about the project manager’s competence and reliability.
  • Deadlines also determine the prices of contracts that, if not met, can affect project profitability.

Often, however, it can be difficult to understand the major difference between effort and duration. So let’s clarify it.

What does duration mean?

Duration is the time required to perform any specific task.

Duration is measured in hours, days, weeks, months, or years and can only be calculated after determining what type and how many resources will go to perform the given task.

Duration is defined as the entire time it takes to complete a specific task, based on the resources allocated to the project.

It is typically measured from when the task begins to the day the task ends definitively. It does not include the free time of resources such as vacations or other non-working days.

Using the same example used in the effort case – painting a house – where you work 6 hours a day for 3 days, the duration for this task will then be 3 days.

Effort and duration relationship

Only when you have an estimate of the effort, you can assess the duration.

This is directly related to the construction of a draft program and involves deciding how many people and resources will be included in the project.

The staffing can, to a certain degree, be changed during the life cycle of the project, but it is necessary to remember that there is a minimum duration required for some activities. For example, it is impossible to make a child in one month by employing nine women to work on the task.

Project effort and duration example

Let’s use as an example a small painting job of a house.

Requirements and estimates

 1 working day = 8 working hours. It means that the painter(s) will work 8 hours a day.

  • The job has an estimated duration of 4 working days with only 1 painter working.
  • There are many painters available to perform the task and all painters are equally productive. The quantity and quality of the work would then be the same for each painter.


If 1 painter works, the duration of the job will be 4 working days or 32 working hours.

If 2 painters work, the duration of the job will be 2 working days or 16 working hours.

If 4 painters work, the duration of the job will be one working day or 8 working hours.


If 1 painter works, the effort for the job will be 4 days/person or 32 hours/person.

If 2 painters work, the effort for the job will still be 4 days/person or 32 hours/person.

If 4 painters work, the effort will always be the same as before, 4 days/person or 32 hours/person.

Project effort and duration relationship

The relationship between the effort of the project and its duration can be better explained using the following formula:

Effort = Duration * Number of resources

the effort

This formula will not work every time, but it gives a good idea of the relationship between effort and duration of a project.

The formula will only work if:

  • The work can be easily distributed among many resources.
  • Resources are not dependant between each other.
  • All resources productivity is considered equal.


When working on a project that has a deadline, understanding and accounting for the difference between duration and effort will allow the project manager to plan the time to dedicate to all activities and meet the deadline.

Moreover, only when project effort and duration will be estimated, it will be possible for the project manager to create the cost estimate.

Effort and duration therefore become two key aspects project planning.

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