Microsoft Project calculates the Summary Level Percent Complete value
based on its immediate subordinate tasks (summary and detail tasks).
This method of calculation can cause the percent complete for a
higher-level summary task to differ from a calculation done by hand if
only the detail tasks and not the subordinate Summary tasks are used.
The Percent Complete for a Summary Task is a weighted average of its
In order for Microsoft Project to speed up calculations, the percent
complete of a summary task is based on its direct subordinate tasks
and subordinate summary tasks percent complete (if any).
Project uses the following calculation:
Percent Complete = Actual Duration / Duration
For a summary task, percent complete is first calculated from its
immediate subordinates, and then actual duration is determined. For a
task, either percent complete or actual duration can be solved.
The following example assumes a default base calendar with no resource
Name Outline Dur Sch St Sch Fin %Comp Act Dur
Top Summary 1 8d 1/1/96 1/10/96 23% 1.8d
Subordinate Summary 1.1 5d 1/1/96 1/5/96 25% 1.25d
task1 1.1.1 1d 1/1/96 1/1/96 50% 0.5d
task2 1.1.2 1d 1/5/96 1/5/96 0% 0d
task3 1.2 1d 1/10/96 1/10/96 10% 0.1d
In Microsoft Project 98/2000, the Percent Complete is 20% instead of 23%
and Actual Duration is 1.6d instead of 1.8d.
Percent Complete of the "Subordinate Summary" is calculated like this:
(1d*50%+1d*0%)/2d=25% [(task1 dur) * (task1 %Comp) + (task2 dur) *
(task2 %Comp)] / [(task1 dur) + (task2 dur)]
Percent Complete of the "Top Summary" is calculated like this:
(5d*25%+1d*10%)/6d=22.5% (=23%) [(Subordinate Summary dur) *
(Subordinate Summary %Comp) + (task3 dur) * (task3 %Comp)] /
[(Subordinate Summary dur) + (task3 dur)]
Because the duration of the "Subordinate Summary" does not equal the
duration of its subordinate tasks, the percent complete of the "Top
Summary" task does not reflect the percent complete values of the
If the Percent Complete of the "Top Summary" was based on only the
subordinate tasks, and not the "Subordinate Summary," it would be
calculated as follows:
(1d*50%+1d*0%+1d*10%)/3d=20% [(task1 dur) * (task1 %Comp) + (task2
dur) * (task2 %Comp) + (task3 dur) * (task3 %Comp)] / [(task1 dur)
+ (task2 dur) + (task3 dur)]