How to Calculate the Duration of a Task?

Estimating the time for a task or a project is a guessing game. Here are three things to consider as you approach this project management exercise:

• We have trouble estimating the duration of a task or activity
• We tend to take the time allotted by our manager rather than the time we so need to do a task.
• We should always expect slowdowns on the project schedule.

Even if it seems difficult to calculate the duration of a task, you should calculate all the variables as best you can and determine a window in which you can be certain that the work will be completed.

Here are 6 methods that will allow you to estimate the duration of tasks in order to better plan and distribute them within the team.

The 9 essential techniques for an effective distribution of tasks

1. Professional judgment

Use the expertise of a team member who knows exactly the task at hand. This collaborator can tell you how long it will take to complete the task based on their previous experience.

If you don't have access to information internally, you can call in an expert to help you.

2. Collective judgment

You can also take advantage of the overall experience of the team. Discuss this question together and make an estimate based on the feedback obtained during this conversation.

This approach may lack precision, but it can be a good way to reach consensus, especially if you don't have experience estimating task length.

3. Estimation by analogy

One of the most common methods: basing your estimates on the results of a previous project. If your company has already completed a similar project and you can access information about this previous task, this will give you a good idea of how long to expect for the same type of task.

4. Parametric approach

If the task you are evaluating is relatively simple and repetitive, you can perform calculations to estimate the overall duration of the activity. For example, if it takes one person an hour to dig a hole and you need ten holes, it will take ten hours of work. If you double the resources and have two excavators, it only takes five hours.

The calculation required for a parametric approach is as follows:

Estimated workload = unit workload X number of units

5. Decomposition method

With this method, you need to break down the activity into tasks, but also into sub-tasks and sub-sub-tasks. The objective is to reach a level of precision sufficient to make an effective calculation.

Based on your experience, knowledge, or historical data, estimate the time required to complete each item.

By then adding up each sub-task, you will get the estimate of the activity you want to measure. Consider adding a safety margin to account for possible delays and unexpected events.

6. The three-point calculation

As part of the three-point calculation, you take into account median, optimistic and pessimistic scenarios. This allows you to obtain a realistic time range to optimize your chances of success. By taking into account possible uncertainties, it is indeed much easier to prepare for them effectively.

Here is the calculation to perform to estimate the duration of the tasks:

Task duration = (optimistic duration + pessimistic duration + 4 x probable duration)/6

Optimistic and pessimistic durations respectively refer to a situation where everything is going smoothly and nothing is going according to plan. The probable duration is a classical average estimate.

7. Historical data (or similar estimate)

Base your estimates on the results of a previous project. If your company has already completed a similar project and you can access the time spent on a similar task, this will give you a good idea of how long the same task will take.

Again, if you do not have this information internally, you will surely be able to rely on partner companies or published data on your industry.

This type of estimate is quick, but you won't get extremely accurate results.

8. Statistical and mathematical analysis (or parametric estimation)

If math wasn't one of your favorite subjects at school, you wouldn't like this part. If the task you are evaluating is relatively simple and repetitive, you can use simple calculations to calculate the overall duration of the activity.

Example: if it takes one person one hour to dig a hole and you need ten holes, it will take ten hours of work. If you double the resources and have two excavators, it only takes five hours. If you bring a machine that works at twice the speed of a person, it will only take two and a half hours.

Not always applicable but effective on some simple tasks.

9. Working from a range (three-point estimate)

Establish the most likely, best, and worst timescales for the task. Then, add up the durations for best and worst cases, plus four times the most likely. Divide by six.

This gives you an estimated duration that takes into account the uncertainties in the estimate but weights the result more heavily toward the most likely outcome.

Here is the equation:

Task duration = (optimistic duration + pessimistic duration + 4 x probable duration)/6

• Optimistic duration: everything goes smoothly
• Pessimistic duration: just the opposite of optimistic duration
• Probable duration: most likely duration

NB: the probable duration may be the same as the optimistic duration.

It's a great way to balance the opinions of multiple experts on the team who all feel they know how long it will take.

In practice, it is the technique that comes closest to reality.

What are the common challenges in estimating task duration?

Estimating the duration of tasks is a recurring challenge in project management. Several factors can influence the accuracy of these estimates, and it is important to be aware of them to minimize the risks of delays and budget overruns.

The first pitfall is the tendency to simplify estimates. Based on normal conditions, we sometimes forget to take into consideration the interferences that always exist in an unpredictable environment.

In order to get closer to reality, it is important, as mentioned above, to consider optimistic, pessimistic and probable estimates.

Various biases can also occur during the calculation. This is particularly the case for the project manager who, wanting to be perceived as effective and not wanting to afford delays, always opts for the longest possible duration.

While it is difficult to get rid of biases during analyses, it is essential to understand them in order to refine your calculations as much as possible.

What tools can help estimate task duration?

There are numerous tools for estimating the duration of tasks. Wimi, as a complete collaborative platform, offers several functionalities that can help you in this task

The task and sub-task management function, for example, allows you to break down your projects for better granularity and a more accurate estimate. You can assign durations to each task or subtask and then visualize the whole thing in a Gantt chart.

Collaboration tools, on the other hand, are perfect for involving the team in the estimation process. Each member can also comment on tasks and suggest time adjustments.

Finally, tracking the time spent on tasks is ideal for comparing the estimated time to the time actually spent on each task. This makes it possible to refine the estimates for future projects.

Estimating the duration of a task is essential to assess the time you need to devote to a project: you now have the tools to do it optimally. One project management software with a task manager such as Wimi also allows you to estimate the duration of your daily tasks.