How to Estimate Time On a Project

As you start to estimate time on a project ask yourself ‘Am I clear on what needs to be delivered’.

The analogy here is ‘Start with the end in mind.’

What are you delivering and what tasks must be completed?

Then develop a list of tasks, including linking the dependencies.

From there it is time to estimate how long each of these tasks, or sets of tasks will take.

Know who is on your team

You need to begin with a good idea of the staff who will be working with you to deliver the project.

What are their strengths, what are their weaknesses; what skill sets do they bring to the table?

Are these people experienced in delivering project similar to what you are about to embark on?

Will these people be available to you for the duration of your project?

Are these team members working full time on your project, or only part time?

All of these things will impact on your time estimation.

If you have very skilled staff working on the project, with experience on similar projects, they will have an understanding of the time it will take to complete their work.

On the other hand, if you have staff who are not as skilled, and have not undertaken this type of project before, it will be harder to estimate how long things will take.

Involve the team to estimate the time

Estimating the time by yourself is not a valuable thing.

This is especially true when you don’t have the knowledge or skills that match those required to complete your project.

The most valuable thing you can do to ensure more accurate estimation is to involve project team members in your estimating.

A good way to go about this is to send each team member, or work stream the tasks that you think need to be completed.  Ask them to validate the list and estimate the time requirement.

This will likely produce a more accurate time estimate than if you try to do it on your own.

And, if they are too busy to do this for you, have a meeting with the team member/stream and walk through it as a group exercise.

The time you take at this point to gather their input will be time well spent and generate efficiencies later on.

Don’t want to involve the team, why not?

What’s stopping you from asking for help with the time estimation process?

Maybe you think that as a Project Manager it is your responsibility to do the estimating, and yours alone.

You could think that nobody else will give you accurate information.

Or, you might have the idea that others don’t understand what is required to estimate correctly.

Whatever the story you have about not asking for help, drop it!

By not involving the team, or others, in the estimation process you are contributing to project failure.

Yes, even before the project has begun.


When a task hasn’t been done before, what do you do?

This can create a bit of a dilemma for you and it is possible to come up with a reasonable estimate.

Talk to people who may have completed a similar task.

Look at the type of work required to complete the task, at least your idea of it.

Then find people who do that type of work and talk to them.

Lots of tasks may not be exactly the same, and yet the process or skill set may be similar.

Considering all of these possibilities will give you some ball park numbers to begin with.

Be aware of the assumptions you are making

As part of your time estimation process, whether with the team or alone, you are likely to have assumptions.

Be very aware of these.

List them down.  Validate them with others.

These are the things that are likely to trip you up and mean that your estimation is way off track.

It would only take one wrong assumption to add a lot of time to the delivery schedule.

Get your assumptions out in the open.

Do you have any expectations?

Expectations can trip you up just as much as assumptions.

What expectations do you have about the work to be carried out?

And just as importantly what expectations do you have about the team members working on the project?

If you have an expectation they will work 10 hours per day for six months, you need to call this out.

They might think they will be working eight hours a day.

This mismatch in expectations will cause you BIG problems with your delivery schedule.

Are you caught in the ‘Planning Fallacy’

You may or may not have heard of the ‘Planning Fallacy.’

This is the phenomena

wherein people underestimate the time it will take to complete a future task, despite knowledge that previous tasks have generally taken longer than planned.

Research shows that this is about holding two opposing beliefs. You know instinctively that something will take longer than you think, based on your past experience.  Yet, you believe that your current forecast is realistic.

You may do this because your view of how long the task will take is based on your own view of it.

In doing this you may also be focused on the past and not on the future.

The bottom line is, if you notice you have an insular view of your estimating, stop and go talk to someone else.

Don’t provide a ‘Rough Order of Magnitude’ (ROM) estimate

Rough Order of Magnitude estimates are the death knoll of any project.

How on earth can you provide a costing based on a plus or minus estimate that can range from -25% to +75%

You can’t.

The whole purpose of you providing time estimates is to enable costs to be figured out.

What resources are required and how much will it cost, to deliver this project, based on the time estimates?

You are wasting your time if you provide a ball park figure.

Be careful adding Contingency Hours

If you are considering adding contingency hours I would recommend against it.

Contingency hours are supposedly to reflect uncertainty or risk associated with your estimate.

There shouldn’t be uncertainty with your estimate.

You want to be clear on what is required and get into the detail of how that will be undertaken.

Only by doing this will you diminish the uncertainty.

Risk at any level needs to be mitigated.

If resourcing is a risk, it needs to be called out and managed in a different way.

Study project lessons learned

Your company may have a PMO that collects lessons learned from its projects.

Go and talk to the PMO and gather lessons learned about similar projects.

Study where the problems highlighted lay and if these same things will impact your project.

Often times these valuable lessons go untapped.

Yet they can provide very useful insight into problems areas for project delivery.

The best project time estimates are based on clarity

The clearer you are on what needs to be delivered, and this may start with business requirements, the easier the estimation process.

With your assumptions and expectations understood and validated everyone involved is clear.

Understanding possible problem points and what additional time is required to work through them, makes estimating more accurate.

Be open to asking more questions to gain clarity.

You will be glad you did.

The more accurate your estimate before the project starts the more likely project success is.


Planning Fallacy Sources: