An interesting question about resource calendars in the Project Standard and Professional user forum prompted me to write this blog post article. After using Microsoft Project for over 21 years, one of the nuggets of wisdom I have gleaned from this software is, “Always trust the schedule.” When you assign resources to a task, Microsoft Project will schedule the task according to the working schedule shown on the calendar for each assigned resource. My experience has shown me that the schedule of the task will always be correct, although you may need to dig a little deeper to determine WHY the software scheduled the task the way it did!
For this blog post article, I will individually assign resources with different working schedules to the task shown in Figure 1. With no resources assigned, notice that the Design task has a Duration value of 5 days, a Start date of 6/3/19, and a Finish date of 6/7/19.
Figure 1: Design task with no resources assigned
Consider the following examples to learn more about how resource calendars impact the schedule of the tasks to which the resources are assigned.
Resource Calendar with a Standard Working Schedule
The working schedule for Terry Uland is displayed in the Change Working Time dialog shown in Figure 2. His working schedule follows the default Standard calendar with Monday – Friday set as working days and Saturday/Sunday set as nonworking time. Notice in the dialog that the Terry’s normal workday includes 8 hours of work from 8:00 AM – 12:00 Noon and 1:00 – 5:00 PM.
Figure 2: Standard working schedule
When I assign Terry Uland to the Design task with a Units value of 100% and 40 hours of Work, there is no surprise in the resulting schedule. Notice in Figure 3 that the Design task still has a Duration value of 5 days, a Start date of 6/3/19, and a Finish date of 6/7/19.
Figure 3: No change to the task schedule
Resource Calendar with Scheduled PTO
The working schedule for Mickey Cobb is displayed in the Change Working Time dialog shown in Figure 2. Her working schedule follows the default Standard calendar but includes two days of planned PTO on June 6-7, both of which are marked as nonworking time.
Figure 4: Standard working schedule with planned PTO
When I assign Mickey Cobb to the Design task with a Units value of 100% and 40 hours of Work, notice in Figure 5 that Microsoft Project reschedules the task to finish on Tuesday, June 11, instead of Friday, June 7. Notice also that the Duration of the task remains at 5 days. This is because Duration is calculated as the number of working days for the task, which in this case is still 5 days.
Figure 5: New schedule includes PTO
Figure 6 shows the working schedule for Mickey Cobb on the Design task in the Task Usage view. Notice she is scheduled to work Monday through Wednesday of the first week, with no work scheduled on Thursday and Friday due to her planned PTO, and to work again on Monday and Tuesday of the second week. Thus, her working schedule on this task is correct according to the schedule shown on her calendar.
Figure 6: Task Usage view for Mickey Cobb
Resource Calendar Includes Weekend Work
Larry Barnes is a member of a dedicated project team that does weekend-only software upgrades and small implementations. Because of this, his normal working schedule is Wednesday through Sunday, with Monday and Tuesday as nonworking time, as shown in Figure 7.
Figure 7: Working schedule includes weekends
When I assign Larry Barnes to the Design task with a Units value of 100% and 40 hours of Work, notice in Figure 8 that Microsoft Project reschedules the task to start on Wednesday, June 5, and to finish on Sunday, June 9. Thus, his working schedule on this task is correct according to the schedule shown on his calendar.
Figure 8: Task includes weekend work
Resource Calendar with 4-Day Work Week
The working schedule for Cindy McNair is 4 days/week and 10 hours/day, as shown in Figure 9. Notice in the Change Working Time dialog that she works Monday – Thursday from 8:00 AM – 1:00 PM and 2:00 – 7:00 PM, with Friday – Sunday set as nonworking time.
Figure 9: 4×10 work week
When I assign Cindy McNair to the Design task with a Units value of 100% and 40 hours of Work, notice in Figure 10 that Microsoft Project reschedules the task to finish on Thursday, June 6. Thus, her working schedule on this task is correct according to the schedule shown on her calendar.
Note: Notice that the Duration of this task remains at 5 days, even though the task schedule spans only 4 days. This behavior is not a bug; it occurs when there is a difference between the resource’s working schedule and the default Hours Per Day value in Microsoft Project. For this task, the Duration was calculated using the formula, Duration = Work/Units x Hours Per Day, where the Hours Per Day value is 8 hours.
Figure 10: Task scheduled over 4 days
College Intern Resource Calendar
Calvin Baker is a student Marquette University and works for our company as a college intern. He attends classes Monday – Wednesday and works full-time as our intern only on Thursday and Friday. You can see his schedule in the Change Working Time dialog shown in Figure 11.
Figure 11: College Intern working schedule
When I assign Calvin Baker to the Design task with a Units value of 100% and 40 hours of Work, notice in Figure 12 that Microsoft Project reschedules the task to start on Thursday, June 6, and to finish on Thursday, June 20. Because he only works 2 days/week, the software schedules the task with 2 days of work the first week (16 hours), two days of work the second week (16 hours), and Thursday only of the third week (8 hours). Again, notice that the Duration of the Design task is 5 days because he is scheduled to work only 5 days during the time span of the task.
Figure 12: College Intern schedule applied
Figure 13 shows the schedule of the Design task in the Task Usage view. Calvin Baker’s working schedule on this task is correct according to the schedule shown on his calendar.
Figure 13: Task Usage view of College Intern schedule
Everyone Assigned
By now you should be convinced that Microsoft Project does correctly schedule each task according to the working schedules shown on the calendar for each assigned resource. But perhaps you are wondering what would happen if I assigned all the preceding resources to the task. Figure 14 shows the Design task with all five resources assigned with a Units value of 100% and 40 hours of Work. The task schedule for this task now represents a conglomeration of the schedules of all five resources.
Figure 14: All five resources assigned to the Design task
Notice in Figure 14 that the Duration of the Design task is now 13.5 days. The task spans from the Start date of the earliest starting resource (June 3) through the Finish date of the latest finishing resource (June 20). To see how the Work is applied for each resource assigned to the Design task, examine the Task Usage view shown in Figure 15. You can clearly see that Microsoft Project correctly scheduled the Design task based on the working schedule shown on the calendar of each of the five resources assigned.
Figure 15: Task Usage view with all resources assigned
Tom Burzynski
Great description Howard, as always! You demonstrated a method of investigation that I always use when in doubt about MS Project…lay down some tasks and experiment…it does not take much time and you learn so much about this tool and all the scheduling permutations. Thanks for pulling back the curtain on this great topic. So which calendar take precedence when you have a resource calendar, a task calendar assigned to the task, and of course the overall project calendar. Enjoyed the read.