Activity Schedule Calculation
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• If your project planning process does not include resource assignments, the activity schedule is controlled manually and you can disregard the scheduling calculations described in this topic.
• The estimated start and estimated finish dates are determined by the scheduling constraint type. For more information, see Activity Date Constraints.
• For examples of how each of the formulas below work, see Basic Activity Calculation Example.
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The plan activity schedule is calculated using the following fields:
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Duration
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The duration is the amount of working time allotted to a plan object.
When creating or editing an activity, you can set the duration using the Duration field or the Estimated Finish Date field.
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Work
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Work is the estimated or planned amount of time required to complete the activity.
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Resource Units
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Resource units are the percentage of workday hours that the resource can devote to the activity:
Resource Unit Percentage = Activity Work Hours/Daily Work Hours*100
For example, if you assign 50 units to a resource, the actual amount of time that resource can spend on project work depends on the plan calendar:
• Standard—Each work day is 8 hours. At 50 units, the resource can work 4 hours per day on the activity. This amount to 20 hours per week in a 5-day work week.
• 24 Hours—Each work day is 24 hours. At 50 units, the resource can work 12 hours per day on the activity. This amounts to 84 hours per week in a 7-day work week.
Using resource units as a scheduling mechanism supports projects that include resources with unique work calendars. Calculating resource units as a percentage provides more visibility to project managers when a resource might be overextended. If the resource units exceed 100% for a particular resource, then the project manager knows that the activity schedule needs to be adjusted accordingly.
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The value for either Duration, Resource Units, or Work is automatically calculated depending on the order in which you enter information when creating the activity.
You can manually enter information into two of these fields; the third is calculated using the following formulas:
• Duration = Work/Resource Units
You provide values for the Work and Resource Units attributes; the Duration attribute is calculated.
The number of days it takes to complete a task is calculated based on the amount of work and resource availability. In other words, the total amount of work required is divided by the amount of work that can be completed each day.
• Work = Duration*Resource Units
You provide values for the Duration and Resource Units attributes; the Work attribute is calculated.
The number of hours spent on a task is calculated based on the duration and resource availability. In other words, how many days the activity requires is multiplied by the number of work hours completed each day on the activity.
• Resource Units = Work/Duration
You provide values for the Duration and Work attributes; the Resource Units attribute is calculated.
The number of hours resources spend each day on a task is calculated based on how much work they have and how long they have to do it. In other words, the total amount of work required is divided by how many days the resource has to complete the work.
If you edit the activity to change the scheduling attributes, how the activity is rescheduled depends on the constraint type and the Task Type and Effort Driven attributes.
For examples of how each of these formulas work, see Basic Activity Calculation Example.