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Assigning Resources with Different Working Schedules

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

 

Dale Howard
Written by Dale Howard

Dale Howard is the Director of Education for PROJILITY. He has used Microsoft Project since version 4.0 for Windows 95 and he has used the Microsoft PPM tool since the first version of released as Project Central in the year 2000. He is the co-author of 21 books on Microsoft Project, Project Server, and Project Online. He is currently one of only 28 Microsoft Project MVPs in the entire world and one of only 6 in the United States.

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4 Comments
  1. 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.

    Reply
  2. Tom — Thank you for your extraordinarily kind comments about my MPUG article. To answer your question, the Task calendar takes precedence and controls the schedule of the task, but only IF the user selected the Scheduling Ignores Resource Calendars checkbox when setting the Task calendar. If the user does not select the Scheduling Ignores Resource Calendars checkbox, Microsoft Project schedules the task using the COMMON WORKING TIME between the Task calendar and the calendars of the resources assigned to the task. Hope this helps. — eDale

    Reply
  3. Howard, good stuff. I am an Open Workbench User with connection to Clarity. I teach a class on Effort Based Scheduling and i’m trying to get MSP to model the behavior of OWB.

    1. OWB Duration = ETC / resource availablitly vs. MSP which is Duration = Work (not eTC) / units (task availability)
    2. Resource availability (Max in MSP parlance) can be variable. That is for March I could be available 80% but in April 50%. OWB is sensitive to the change in availability. That is it want let me go over 50% in April
    3. In MSP, when I make the availability variable off the resource sheet to reflect the scenario above, resource leveling just gives me that there is an over-allocation, it doesn’t “fix it” for me. Is there a way to make leveling sensitive to this with out having to modify the units for each task affected by the overallocation?
    4. Also, In OWB when I set the priority, a resource conflict gets resolved where the higher priority task gets precedence. When I attempt this with resource leveling in MSP the results are not unpredictable. When priorities are equal and I set leveling to ID only, it behaves the same way as OWB in that WBS order takes precedence.
    5. Any guidance on this would be appreciated. It is the one critique I have of MSP in that it can’t (maybe due to my lack of competence) do a schedule with resource constraints where there are no dependencies just priorities and resource availability, OWB / Clarity appear to have a leg up in this regard.

    Thanks in advance.

    Reply
  4. Steve —

    Thank you for your questions. Keep in mind that Microsoft Project is not Open Workbench, so I would not expect them to work the same. To answer your questions:

    1. In Microsoft Project, Duration = Work/(Hours Per Day x Units). The Hours Per Day value is 8 hours by default. You can find this value by clicking File > Options > Schedule. I refer to this formula as the Duration Equation, and it is the foundational formula on which all scheduling resides in the software. There is no way to make it work any different.

    2. Microsoft Project will never stop you from creating an overallocated resource. This is just how the tool works.

    3. No, when you use the built-in leveling tool in Microsoft Project, the software will NEVER adjust the Units value to resolve the overallocation. The leveling tool can only delay tasks (or assignments) or split tasks (or assignments).

    4. In Microsoft Project, you CAN set the Priority number for each task assigned to an overallocated resource. Double-click the task in question. In the Task Information dialog, you see the Priority value on the General page. You can set a Priority number between 0 and 1000 for each task. To force the leveling tool to consider Priority number first, click the Resource tab to display the Resource ribbon. In the Level section of the ribbon, click the Leveling Options button. In the Resource Leveling dialog, click the Leveling Order pick list and select the Priority, Standard value, and then click the OK button. Keep in mind that Microsoft Project considers five leveling factors when it levels an overallocated resource, and another factor may carry more weight then the Priority number, even though Priority number will be considered first.

    5. See above for my answers.

    Hope this helps. — eDale

    Reply

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