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Auto-Scheduling Tasks in Microsoft Project

When, why, and how to use task auto-scheduling

Auto-scheduling is one of the major advantages Microsoft Project holds over applications like Microsoft Excel. Excel will happily hold your task data in rows and columns, but Excel cannot take account of task dependencies, hierarchies, and resource constraints. Project can, largely through the auto-scheduling feature. In fact, arguably, auto-scheduling is the main reason why you would even bother using Project at all!

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Manual vs. Auto-Scheduling

  1. When you first add tasks to a brand-new Microsoft Project plan, you will notice that they are in Manually Scheduled mode, as indicated by the light blue thumbtacks in the Task Mode column:

    Tasks initially added to a blank Microsoft Project plan are in Manually Scheduled mode.

  2. In this simple example, we have a summary task and three subsidiary tasks, all manually scheduled. Task 2 cannot begin until Task 1 finishes (this is known as a finish to start dependency). Likewise, Task 3 cannot begin until Task 2 finishes. Each task will take a week to complete.

    Notice that none of this vital information is captured in the Summary Task A line. Summary Task A should run from December 15, 2020 to January 4, 2021, based on three sequential tasks that comprise this larger piece of work. Instead, Summary Task A runs for a single day on December 15. There are red squiggly lines under the finish dates of all four tasks, indicating something is amiss, but that is all Project has done for us.

    Now, watch what happens when we switch the Task Mode from Manually Scheduled to Auto Scheduled. We'll start by only switching the three subsidiary tasks:

    Our tasks, with the subsidiary tasks auto-scheduled but the summary task still manually scheduled.

  3. Beyond the change of icon in the Task Mode column, and the reduction in red squiggles, not much happened, right? Summary Task A remains at its erroneous duration of 0 days. The durations, start dates, and finish dates of Tasks 1, 2, and 3 are unchanged. That's because dependencies are taken into account even when tasks are manually scheduled. So when we added the dependencies in the Predecessors column to the manually scheduled Task 2 and Task 3, the start and finish dates of those two tasks moved at that point, without the need for auto-scheduling.

    OK, let's switch Summary Task A over to Auto Scheduled mode.

    Our tasks, with Summary Task A switched to Auto Scheduled mode.

    Finally, we see a difference! Our summary task now runs from the earliest start date to the latest finish date of its component tasks, as we would expect. Also, the red squiggly lines that Project uses to flag scheduling problems have disappeared. As far as Project is concerned, this is a complete and logically consistent set of tasks.

    In summary, if you have a project plan with multiple levels of tasks, you should leverage the auto-scheduling capability of Microsoft Project to ensure tasks start and end when they are supposed to. On the other hand, if your plan is simpler, containing only dependencies, you might be better off staying in the Manually Scheduled mode of Project. Or, better yet, if your plan has no dependencies at all, you may be better off using a simpler and more widely adopted tool such as Microsoft Excel.

Changing the Default Scheduling Mode for a Project

As you have seen, there are benefits and drawbacks to both manual and auto-scheduling of tasks in Microsoft Project. Auto-scheduling is the most accurate scheduling mode, but also the most constraining. Especially in the early stages of a project, it can be frustrating to have dates change on you as you're manually inputting data that you may have jotted down on a piece of paper during a planning meeting.

Microsoft anticipated this problem by setting the default scheduling mode for new tasks to Manual. That allows you to digitally "jot down" your schedule without taking into account task hierarchies and resource constraints.

In some cases, however, it might make more sense to start a project with all tasks in Auto-Scheduled mode. For example, suppose you have been asked whether a given sequence of tasks is even feasible given the interrelationships and resource constraints in the project. If you enter your new tasks with auto-scheduling on, you’ll quickly find out whether there are any major problems.

To change the default task mode in Microsoft Project, first select any task (below we have selected Task 3). Go on the ribbon to the Task tab and select Mode. Change the selection from Manually Schedule to Auto Schedule.

Changing the default mode for new tasks from Manually Schedule to Auto Schedule.

Now, when we enter a new Task 4, the task is auto-scheduled as soon as we type in its name. Even though we haven't yet defined our new task's duration, start date, or finish date, Summary Task A is already affected by the addition. The summary task's duration changes from "15 days" to "15 days?", reflecting the uncertainty surrounding its new component Task 4.

Adding a new task to our project in default auto-scheduling mode.

If we further refine Task 4 to be a week in duration, and to require the completion of Task 3, then auto-scheduling adds a week to Summary Task A's duration. The summary task formerly ended on January 4, 2021; now it ends on January 11.

Refinements to the new Task 4 immediately affect the dates and duration of Summary Task A.

Last Modified: December 16, 2020