Time Estimation in Project Management: Tips & Techniques


“If only there was more time,” goes the lament. Project managers sing this sad song, but don’t expect the chorus to join in. Keeping to the project’s schedule is one of the three prongs of the triple constraint.

Time rules all projects. It’s of paramount importance to everyone involved, from stakeholders to team members. The clock is always ticking. The best a project manager can do is develop an accurate time estimate for how long it will take to satisfactorily complete the project.

Time Estimation Matters

A 2018 study by the Project Management Institute (PMI) stated that poor time estimating is the root cause for 25 percent of failed projects. With those odds, whoever can figure out how to stop the clock is going to be a super project manager.

While it might be impossible to stop time, it is possible to overcome its impending approach as it relates to the project’s end. Looking into the future to determine how much time it will take complete project tasks allows for an estimation. But it’s not sorcery, it’s well-executed project management techniques.

So, what are some of those tips and techniques for better project estimation? They run from simple to the complex. We’ve listed some of the tried and true time estimation methods below. See which work best with your style of project management.

screenshot of Gantt chart in ProjectManager.com
Estimate time and track actual progress vs planned progress with ProjectManager.com. Try It Free

Don’t Fall for the Planning Fallacy

The planning fallacy refers to a psychological tendency for people to underestimate the amount of time it will take to complete a task. People often neglect to take historical data into their calculations and think only of what must be done, which makes estimations ill-informed.

Estimation mishaps are usually caused by two factors: historical data (failing to look back at how long a task had taken in the past) and making an assumption there will be no roadblocks to complicate the path forward. The latter is defined by another psychological term, optimism bias.

The main lesson to learn from all this psychological profiling is that our gut is a poor estimator of time. Project managers can factor in intuition, but it’s better to have backed up a schedule with hard data. Let’s take a closer look at a couple of these types of hard data.

Historical Data

First is historical data, which is just a fancy way of saying: you’re not the first person to do this. So look back at past examples and see how long they took. More than just anecdotal, historic data is information on past events and circumstances related to a certain subject. Analysis of this data is informative.

Historical data is also broad. It’s a wide net around whatever subject to which it is related. There can be a range of information, here, from press releases to financial reports, log files and project and product documentation.

In order to have a consistent time estimation, historical data is important, but it’s not cheap. Gathering historic data costs money, time and effort. But even a small amount of historical data is better than none, in that it points to precedent and can lead planning on a path that is more accurate in terms of estimating the time it will take the project to complete.

Know What Needs to Get Done

Historical data only works, however, if a project manager meets beforehand with the stakeholders and has a clear understand of what the goals and the objectives of the project in fact are. This is only the first step towards a full understanding of the project.

There are many tools that can help with identifying the tasks necessary to complete the project successfully and a more accurate schedule can emerge. Just one of those tools is a work breakdown structure (WBS), which is a way to take project deliverables and break them down into small tasks. This not only makes the work more manageable; it helps with time estimations.

Track Time Thoroughly

But a project isn’t only executing tasks. There are other, seemingly insignificant, activities that eat up time. Don’t forget to include time it will take to conduct meetings, both with the team and reporting to stakeholders. There’s also communications in general, testing and other activities that occur over the course of the project phases.

Consider using ProjectManager.com’s timesheet software to track time spent on your project. This way you can make better estimations for future tasks and projects. Plus, when it’s rolled into your larger project management software, this time data syncs with all of your other project management tools.

ad for project management software

Talk to the Experts

You can do much estimating on your own, and even seek historic data to place your project in a larger context, but time estimating should not be done in isolation. Speaking to a person who has worked on similar projects will uncover nuance and details not found in dry data.

Experts are great, but there might be people close by, untapped. We’re speaking about your colleagues. Teams are assembled for expertise and experience. Talk to them, brainstorm, listen to their ideas and concerns.

Chances are team members have done similar projects and have resolved issues that might have sidetracked them in the past. They can give you thoughts about efficient and effective planning, including a better sense of how long everything will take.

Bottom-Up and Top-Down Estimating

Bottom-up estimating is breaking down larger tasks into smaller, more detailed tasks. Then you estimate how much time it will take to complete each task. Estimating time at a granular level also increases accuracy.

Top-down estimating is an analysis in which you first develop an overview of the expected timeline. Then using past projects, experience and historic data as a guide, determine what the time estimate is.

Both time estimate techniques work well together. Compare the results from both, and you’ll have an even more accurate estimation of time needed to complete the project. If the two don’t align, it doesn’t mean one or the other is wrong, just that you must refine your estimate.


PERT (Program Evaluation and Review Technique) comes from the U.S. Navy, where it was used to estimate time it would take to develop ballistic missiles. What PERT does is manage probabilities.

It starts with a WBS, breaking down tasks into smaller activities, which is then placed in a Gantt chart. When comparing PERT Charts to Gantt Charts, on a Gantt chart, any dependent tasks—tasks that can’t start until another is finished—are linked. Each task is a line on the Gantt chart, starting at one point and ending at the completion.

The Time Estimation Formula

For each of these activities estimate these times:

  • optimistic time (O): the fastest an activity can be completed
  • most likely time (M): the project manager’s required delivery date
  • pessimistic time (P): the longest amount of time given to finish the activity

To figure how long the activity will take, complete this equation, with E representing expected time for completion:

E = (O + 4M + P)/6

To calculate variance, with V being variance, use this equation:

V=[(P – O)/ 6]^2

After calculating E and V for each activity, add up the Es, and you have an accurate time estimate for project completion.

Using ProjectManager for Time Estimation

For increased accuracy when uploading initial data, use the online Gantt chart from ProjectManager.com. Linking dependent tasks is easy. Editing task duration is as simple as dragging and dropping the timeline. You can even automatically calculate the critical path.

pm software scheduling gantt chart

Once you have an estimate and are ready to start the project, you’re already in a robust project management software with real-time status updates, easy task assigning, and a collaborative platform to help teams communicate and work together more productively.

ProjectManager.com is a cloud-based project management software that keeps project managers, teams and stakeholders working together more efficiently. Online Gantt charts add collaborative tools to scheduling and a real-time dashboard collects data as it is updated, which then displays project metrics that are easy to filter and share. Take a free 30-day trial and see how it can help you estimate time on your projects better.

Related Posts