time estimation

When planning to begin an exciting new project, project managers are often asked, “how long will you take to complete the project?”

Time is a finite resource since our life-span is short. Even if we try to, we cannot escape the limitations of time. This is why estimating time is among the essential aspects of managing projects.

Sometimes, project managers are not asked about the estimation but a deadline is forced down their throat. The client or their manager just directs them to complete activities by a specific prescribed date.

Generally, when a deadline is imposed, most project managers try to finish the job within the specified time frame.

They do everything in their power to meet the deadline but this too should not be done without estimating. The estimation should be still done even when somebody has set a deadline for you. You should back-calculate and try to fit in your tasks within the available time. This is a difficult job but not an impossible one.

Let us try to answer one basic question about estimation – can duration estimation be done without making assumptions?

What are Assumptions?

A project assumption is a statement that is believed to be true. It is based on our knowledge, experience, and available information. You will see assumptions in every project. It is next to impossible to do project planning without making assumptions.

The PMBOK Guide states that “the supporting documentation should provide a clear and complete understanding of how the duration estimate was derived”. The Guide further prescribes that the supporting detail should include documentation for all assumptions made.

Clearly, duration estimation cannot be done without making assumptions. However, for the moment, let us think that it is possible to estimating without making assumptions.

Let us ASSUME that there is a way to find EXACT ESTIMATES without making any assumption.

Oxford dictionary states that an estimate is “a judgment that you make without having the exact details or figures about the size, amount, cost, etc. of something”

“Exact estimates” is an incorrect phrase – it is an oxymoron. But, let us humor ourselves and try to check if there could be exact estimates.

Exact Estimates

There will be no project uncertainty if we can ascertain the exact duration beforehand; that is even before we start a project. Let us look at a project scenario and try to do just that.

Let us consider that we would like to travel from SFO to LA by a bus and we wanted to find the exact duration for the travel. To do this, we approached a local bus company and started talking to the operator.

Our conversation with the operator might go like this:

I: How long will it take to travel between SFO and LA?
Operator: Approximately, it should take five hours and forty-five minutes.

I: Are you sure about this?
Operator: Hey! Don’t ask silly questions. What do you think I do for living? I am doing this for the last twenty years.

I: Sorry to hurt your feelings. I just want to be sure about the timing.
Operator: You bet. Maybe fifteen minutes here or there but we will be at our destination.

I: Can you provide me with an accurate figure?
Operator: I did that. You should understand that the answer depends on many factors such as day-time, weather, road conditions traffic, etc.

I: OK. Can you at least confirm that we can reach LA in less than six hours?
Operator: Yes. Most probably.

I: Most probably? Why is that?
Operator: As I said, time of travel depends on many variables. The journey takes less than six hours on a usual day but you can never be sure.

I: So, six hours is only an estimate and not sure-fire figure.
Operator: I don’t know what an estimate is.

I: Have you made any assumptions for determining this figure?
Operator: I have already said that I am a skilled driver. I do not make any assumptions about my work.

If we follow the conversation, you will notice that the operator is not able to give us a 100% accurate time estimate.

While conversing, he is stating assumptions without realizing that those are assumptions – assumptions about weather, road conditions, and traffic etc.

The operator’s estimate could be pretty accurate. However, it is far from being perfect.

How to do Better Estimation?

You might think that talking to a driver can be hardly considered as a good approach for finding the duration estimates for a trip. That there are better strategies to estimate the duration of a project.

You can argue that one can use a good software for mapping to determine the duration. One can open any app for mapping to enter the start and finish points of the trip; the app will instantly show an estimated duration.

But, then again, this estimate will be an approximate estimate and not an accurate one. Plus, the mapping software would have calculated the time based on certain assumptions like mode of transportation, route, traffic, and weather.

Let us say that mapping software tells us that the travel time for completing the journey is five hours and fifty minutes.

Will this be more accurate than operator’s estimate?

We can’t say for sure. It totally depends on quality of assumptions. Even utilization of modern technology cannot give us accurate results.

The exact time frame can be found out only after the journey has been completed.


In the above example, I have considered an operational task – travel between SFO and LA. This is a routine task for a travel operator but still he has to make assumptions while doing estimation.

Project tasks are different from operational tasks. They involve more uncertainty and tend to have less information at the start of the project. It is more difficult to estimate project tasks.

So, what is the bottom line? Can we do estimation without making assumptions?

Task estimation without assumptions is not possible. You can probably have lesser number of assumptions if the requirements are clearly defined, there are very few uncertainties, and detailed information is available.

Estimation accuracy is contingent on the amount and the nature of the underlying assumptions. Assumptions, themselves, are dependent on the amount of information that is available beforehand.

Do you think estimation can be done without making any assumptions? If your answer is yes, why do you think so?

Please leave a comment below.

Praveen Malik

Praveen Malik is a start-up enthusiast and sales conversion guru. But his first love remain in Project Management. Praveen is a well-renowned speaker, trainer, author, and project management coach. He helps PMP aspirants through his eponymous project management blog.