How to Estimate Project Duration Accurately

Good project management requires an accurate estimation of the schedule estimated to complete a project. There are two basic good reasons for having the right estimates:

  • The schedule estimates are the basis for setting the budget estimates
  • The estimate set the deadlines for the delivery of the project outcomes which sets the expectations from donors and beneficiaries

Project managers often fail to consider the full complexity involved with a project and they underestimate the amount of time needed to implement it. This usually occurs when they are not familiar with the work that needs to be done and forget to take into account the time needed for unexpected events or unscheduled high priority work. 

The first step in estimating time accurately is to fully understand what the project aims to achieve. This involves reviewing the tasks from the Work Breakdown Structure (WBS) in detail so that there are no unknowns. The WBS is the best techniques to list all the tasks in a hierarchical order to identify all the work the project will do.

Once the detailed list of all the tasks is completed, the project team needs to make a best guess at how long each task will take to complete. In this second step, the project manager needs to ensure that within the estimate there is time for project management tasks and time for the following events:

  • Accidents and emergencies
  • Project meetings
  • Holidays and sickness from project team members
  • Meetings with stakeholders, donors, and beneficiaries
  • Breakdowns in equipment, power failures
  • Missed deliveries by suppliers or consultants
  • Interruptions caused by social, political or natural events
  • Donor audits

The above factors will cause an increase in the length of time needed to complete a project and should be taken in consideration when making changes or modification to the schedule. As the project makes progress it is a good practice to review the assumptions made for estimating the tasks and activities of the project. The initial assumptions may have changed, which forces the project to re-estimate the duration of the project activities.

For example, an initial estimate for a capacity-building project, had a duration of 10 months, after an analysis of the complexity and demands from stakeholders, the project manager added an additional month to the original estimate and another month to account for unplanned events. The new estimate is now 12 months. With this estimate, the project manager has the confidence that the people assigned to the project will have the time they need to deliver the required outputs.

Here are some tips for estimating project duration:

  • The first step towards making good time estimates is to fully understand the problem to be solved.
  • Prepare a detailed list of tasks that must be achieved. This list should include all the administrative tasks and meetings you need to carry out as well as the work itself.
  • Finally, allow time for all the expected and unexpected disruptions and delays to work that will inevitably happen.

Don’t underestimating the length of time needed to implement a project. If you underestimate the time, not only do you miss deadlines, you also put other project team under unnecessary stress.

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