Background Information

In Microsoft Project, you can completely override the schedule of any task by assigning a Task calendar to the task. Common needs for using a Task calendar might include the following:

• In an organization that normally works Monday – Friday only, you need to schedule a task to be worked on a Monday – Saturday schedule instead.
• You need to schedule task work to be performed 24 hours/day and 7 days/week.
• You need to schedule a task as “weekend only” with work scheduled only on a Saturday and/or a Sunday.

When you apply a Task calendar to a task, Microsoft Project completely reschedules the task according to the schedule shown on the Task calendar.

Applying a Task Calendar

To apply a Task calendar, double-click the task in question. In the Task Information dialog, click the Advanced tab to display the Advanced page of the dialog. On the Advanced page of the dialog, click the Calendar pick list and select the calendar you want to use to override the task schedule (aka the “override calendar”). After you select the override calendar, Microsoft Project activates the Scheduling ignores resource calendars checkbox to the right of the Calendar field, such as shown in Figure 1. In this blog post article, I want to explain the purpose of the Scheduling ignores resource calendars checkbox and to demonstrate how this feature works in the real world.

About the Scheduling Ignores Resource Calendars Option

Consider the following example. Figure 2 shows the original schedule of the Design task before I assign any resources to it. Notice that the Duration of the task is 3 days, that the task starts on a Monday, and finishes on a Wednesday.

Figure 3 shows the new schedule of the Design task after I assign a college intern named Calvin Baker to the task. Because Calvin is a college intern, he only works 2 days/week on Tuesdays and Thursdays. Because of his unusual working schedule, Microsoft Project scheduled the 3 days of work beginning on the first Tuesday available, along with the next Thursday and the following Tuesday.

So that you can confirm his working schedule, Figure 4 shows the Change Working Time dialog for Calvin Baker. Notice at the top of the dialog that that I specified the College Interns custom calendar in the Base calendar field for Calvin Baker. Notice also in the dialog that Tuesdays and Thursdays are the only working days each week, while Mondays, Wednesdays, and Fridays are set to nonworking time.

To confirm the working schedule for Calvin Baker on the Design task, Figure 5 shows the Task Usage view for this task. Notice that Microsoft Project correctly scheduled the work for this task on Tuesdays and Thursdays only, as governed by the College Interns calendar assigned to Calvin Baker.

Although the Design task is currently scheduled on Tuesdays and Thursdays only, I need to override the schedule of this task so that it is schedule for Mondays, Wednesdays, and Fridays. I need to do this to speed up task completion because Calvin Baker does not have any college classes scheduled during the week that the Design task is currently scheduled. To accomplish this, I must assign a custom calendar as the Task calendar for this task. Figure 6 shows the Advanced page of the Task Information dialog after double-clicking the Design task. Notice in the dialog that I selected the M-W-F Only custom calendar as an override calendar in the Calendar field.

In Figure 6 shown previously, again notice the Scheduling ignores resource calendars checkbox to the right of the Calendar field. So, what does this checkbox actually do?

When you select the Scheduling ignores resource calendars checkbox, Microsoft Project overrides the schedule of both the task and its assigned resource, even if that resource does not normally work the schedule shown on the override calendar. In my example, the software will schedule the task, along with Calvin Baker’s assignment, to the Monday – Wednesday – Friday working schedule, even though he normally works only Tuesdays and Thursdays. When you need to completely override the schedule of the task and its assigned resource, remember to select the Scheduling ignores resource calendars checkbox. Figure 7 and Figure 8 show the new schedule of the Design task after applying the M-W-F Only custom calendar in the Calendar field and selecting the Scheduling ignores resource calendars checkbox. Notice that Microsoft Project correctly scheduled the task and Calvin Baker on Monday, Wednesday, and Friday, as expected.

When you deselect the Scheduling ignores resource calendars checkbox, Microsoft Project schedules the task and the assigned resource using the common working time between the override calendar and the calendar of the resource assigned to the task. In this example, the override calendar schedules work on Mondays, Wednesdays, and Fridays. The resource calendar for Calvin Baker, however, schedules his task work only on Tuesdays and Thursdays. Notice that there is no common working time between the two calendars. In a situation such as this, Microsoft Project will display a warning dialog, such as the one shown in Figure 9, alerting you to the lack of common working time between the two calendars.

As the warning dialog indicates, when you apply a Task calendar and there is no common working time between the override calendar and the resource calendar, Microsoft Project applies the override calendar and schedules the task only according to the override calendar, ignoring the schedule shown on the resource calendar. However, in addition to this, the software also displays a warning indicator for the task in the Indicators column. Figure 10 shows the tooltip when I float my mouse pointer over the warning indicator.

At this point, you might be asking, “What if there IS common working time between the override calendar and the resource calendar?” Suppose that the College Interns custom calendar schedules work every Tuesday, Wednesday, and Thursday, such as in the Change Working Time dialog for Calvin Baker shown in Figure 11. Notice that the dialog indicates Tuesday, Wednesday, and Thursdays are working days according to the College Interns custom calendar.

If I assign the M-W-F Only calendar as a Task calendar on the Design task, but do not select the Scheduling ignores resource calendars checkbox, Microsoft Project schedules the Design task using the common working time between the override calendar and the resource calendar for Calvin Baker. In this situation, Wednesday is the only common working time between these two calendars. Therefore, Microsoft Project schedules the task on three consecutive Wednesdays. Figure 12 and Figure 13 show the new schedule of the Design task, now scheduled on three consecutive Wednesdays.

Note: In Figure 12 shown previously, notice that the Duration of the Design task is still only 3 days, even though the task spans what appears to be 11 working days in the Gantt Chart pane. Always remember that in Microsoft Project, Duration is the span of active working time from the beginning of the task to the end of the task. In this situation, only 3 of the 11 days are actually working days, therefore, the correct Duration value for this task is 3 days.

Note: One potentially negative consequence of applying a Task calendar to a task is that this can cause Microsoft Project to designate the resources assigned to the task as overallocated. This normally occurs when the Task calendar schedules a resource to work on one or more days on which the resource does not normally work according to the resource’s calendar. For example, if I apply a Weekend Work Only calendar to a task, and the resource normally works Monday – Friday only, Microsoft Project considers the resource as overallocated because the resource is scheduled to work on days that are nonworking time on the resource’s calendar (Saturday and Sunday). This type of overallocation is what I call a “false overallocation” because it is an overallocation that you cannot level. There is no way to eliminate or hide these types of false overallocations; therefore, I recommend you simply ignore them.