Goal: Estimate task durations

One of the best aspects of using Microsoft Office Project 2007 is that it can calculate a realistic schedule for you, often based solely on task durations and task dependencies that you enter. Sure, you might have other scheduling controls, such as start (start date: The date when a task is scheduled to begin. This date is based on the duration, calendars, and constraints of predecessor and successor tasks. A task's start date is also based on its own calendars and constraints.) and finish dates (finish date: The date that a task is scheduled to be completed. This date is based on the task's start date, duration, calendars, predecessor dates, task dependencies, and constraints.) and calendars (calendar: The scheduling mechanism that determines working time for resources and tasks. Project uses four types of calendars: the base calendar, project calendar, resource calendar, and task calendar.), but those are the exception, not the rule. Because a schedule's accuracy relies so heavily on accurate durations, spending a little brainpower on developing your durations (duration: The total span of active working time that is required to complete a task. This is generally the amount of working time from the start to finish of a task, as defined by the project and resource calendar.) will pay off.

 Tip   This article is part of a series of articles within the Project Map that describe a broad set of project management activities. We call these activities "goals" because they are organized around the project management life cycle: Build a plan, track and manage a project, and close a project.

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Closeup of wristwatch on man's arm

number 1  Start with some basic research     The information that can help you estimate how long certain tasks take to complete can come from several sources.

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Find sources for duration estimates
  • Your own experience     Draw on your own background from times when you carried out similar tasks in this or other projects.
  • The experience of your team members     Consult with the resources who have been responsible for certain types of tasks. If you already have a team in place, have the members develop their own durations for their assigned tasks on this project. This can serve as a commitment from those who are responsible for completing tasks.
  • Previous projects     Review projects that you or other project managers built and tracked. Any actual durations that were recorded can be especially helpful.
  • Industry standards and benchmarks     Find information about task durations that is pertinent to your industry. In books, journals, and on the Web, you can find task lists with recommended durations and other metrics. Professional organizations for your industry are also a good place to find this information.

 Tip   Consider starting small by creating a project that is broken down into small chunks of work (tasks) that can be completed in a month. When the month's worth of tasks is complete, start another month's worth of work. This is the technique that the agile method of project management uses to help reduce the margin of error in task durations, while providing fast feedback about the health of a project.

Build a time buffer into your project

Because you can't anticipate every issue that might delay your tasks, even the most accurate durations need a little "wiggle room." This provides a measure of risk management for your project. There are different ways to build a time buffer into your project:

  • Add a percentage to every duration     If you think a task will realistically take 40 hours to complete, adding a 5% buffer changes it to 42 hours. A 10% buffer changes it to 44 hours. Extra time is built into the schedule, just in case you need it. If you don't need it, this buffer can allow successor tasks to start earlier.
  • Add a buffer task     Add a modest "buffer task" to every major phase of the project, or a sizable buffer task to the project as a whole. If you find that you need an extra day for a task that is slipping, you can remove the buffer task and add its time to the slipping task. Your overall finish date for the phase or the project remains the same.

Number 2  Create a milestone     When you want to identify a significant event in your schedule, such as the completion of a phase, create a milestone in your project.

Number 3  Estimate durations     You can model a project by using best-case and worst-case scenarios to help you accurately estimate the durations for your schedule and to simulate future resource loads and their effect on project timelines.

Number 4  Enter a duration     After you determine how long it will take to complete a task, it is time to enter a duration. Enter an estimated duration if you still aren't sure how long a task will take to complete.

Number 5  Interrupt work on a task     If two tasks occur simultaneously, you can pause the work on the task that starts first, begin the second task, and then start work again on the first task when the second is finished.

Number 6  Create a calendar     To identify working and nonworking time for a specific task, create a calendar. For example, a piece of machinery that is needed to complete a task may be available only on certain days of the week. You can identify the working time on a task calendar, and the task is scheduled accordingly.

Number 7  Assign a calendar to a task      After you create a task calendar, you apply it to the task or tasks that you created it for.

Number 8  Add supporting information about a task     Add more information about a task in the form of notes, documents, and links to Web pages.

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Applies to:
Project 2007