Change a task duration

When you create an automatically scheduled task, Project 2010 assigns it an estimated duration of one day by default. You can modify that duration at any time to reflect the actual amount of time that the task requires.

Note: What happens when you create or change a task duration differs depending on whether you are working with an automatically scheduled task or a manually scheduled task. By default, new tasks are manually scheduled and do not have default durations. To make new tasks automatically scheduled, on the Task tab, in the Tasks group, click Auto Schedule.

What do you want to do?

Change a task duration

Make better estimates

Change a task duration

  1. If necessary, add the task to the project plan. See Create single and recurring tasks for full instructions.

  2. In the Duration column for the task, type the duration in minutes (m), hours (h), days (d), weeks (w), or months (mo).

    Note: Project does not convert the units if you change them. For example, if the duration is 1 day and you want to express it in hours, you must first calculate the number of working hours in a day and then enter the new value in hours.

  3. If the new duration is an estimate, type a question mark (?) after it.

  4. Press ENTER.

Note: In Project 2010, you can change the duration of a summary task (also called a "hammock task") without changing its subtasks. If the duration of the summary task becomes different than the total duration of its subtasks, the difference appears as a red line on the chart portion of the view.

Change the default units

  1. Click the File tab, and then click Options.

  2. In the Project Options dialog box, click Schedule in the left pane.

  3. In the Duration is entered in box, select a duration unit.

Allow estimated durations

Some projects might not use estimated durations for automatically scheduled tasks. If your project does not use estimated durations and you type a question mark in the Duration column for a task, the value is not considered an estimate. To enable estimated durations in your project, do the following:

  1. Click the File tab, and then click Options.

  2. In the Project Options dialog box, click Schedule in the left pane.

  3. Select the Show that scheduled tasks have estimated durations check box.

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Make better estimates

Understand the past

To increase the accuracy of your task duration estimates, use your own experience and those of other people who have worked on similar projects and tasks. Ask questions such as the following:

  • How long did the task take?

  • What challenges did you encounter?

  • What would you do differently if you had to do it over again?

Note any differences between the new task and previous tasks, and account for them when you estimate a task's duration.

Tip: To connect with other project managers, check out project management groups on social networking sites like Facebook or Twitter.

Understand the present: Who and what

Include the following considerations as you estimate task durations:

  • Durations can depend on the experience of the person who performs the task. A highly experienced person can sometimes complete certain tasks more quickly than a less experienced person.

  • Revisit estimates when the work starts. You will know more about the tasks at that point.


You can also derive your estimates by comparing optimistic, pessimistic, and expected durations. This is sometimes referred to as a PERT analysis.

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