Project summary actual duration or % complete lower than those of the sub tasks

Copper Contributor

I have been tracking this schedule for a while. Just noticed that the % complete or the actual duration of the Project summary task is lower than those of the sub tasks. Why is this weird behavior ? what mistake did i do ?Screenshot 2023-01-27 145953.png

8 Replies
Rest assured, it is not weird behavior and you didn't make any mistake. In Project the Percent Complete for a summary line is calculated as:
(sum of all subtask actual durations)/(sum of all subtask durations) * 100%

Apply the above to any summary line, including the Project Summary Task and you should see the value shown.

Hope this helps.

@John-project But why the actual duration of the Project summary task is lower than the actual duration of the sub-summary tasks. For ex., mobilkization is 793 days.. milestone is 939 days.. but Project actual duration is only showing 559. It's weird. 

@aneeshU1 You say it's weird. So what do you think the actual duration of the Project Summary task should be?


Keep in mind that summary lines are NOT tasks, despite with the literature may call them, t hey are simply a summary of data for performance tasks (subtasks that have resources assigned to do something). As such percent complete and actual duration for summary lines will be some form of weighted average for all the subtasks under them. The developers of Project chose the formula I showed as that weighted average.


Here's a simple example. Should the actual duration of the Project Summary task be longer than any of the summary tasks under it just because it's the Project Summary task? Answer, "no".



Hope I clarified it for you.




Nothing weird happening like @John-project said but if you are still not satisfied with his answer, can you please paste a screenshot that also shows Actual Duration, DurationStartFinishTask Calendar.


I have attached the required screenshot. 

Let's say that we have a project of one month duration (31 days).
Now we are at day 15, the project should show the actual duration as 15. 

The other activities can show duration 15 or less, as they all are within this project. But it cannot be more than 15. Am I right?

Screenshot 2023-01-30 071605.png



It seems you have different calendar for Project Summary to the Tasks & Sub-tasks calendar. Assign same calendar and see what happens.


Day 15 does not mean Actual Duration should be 15 days as one of the peeves with MS Project is that it allows tasks to be completed in the future. E.g. if a Task with 31 days is assigned 100% on day 15, MS Project will show actual duration of 31 days and actual finish date in future (day 31).

I think you are interpreting the Actual Duration field as literally meaning a time span from the start to the current date but that is NOT what that field means. I suggest you hover your mouse over the Actual Duration field column heading. That will bring up a short description of how the field is determined. You can also hit the F1 key to bring up the help file for that field.








The %Complete of a summary task is calculated as previously mentioned:


100 x Sum of all actual subtask durations / Sum of all subtask durations


And your Actual Duration = % Complete x Duration /100


Taking into account that the Duration = Maximum Finish date - Minimum Start date, of all its subtasks, counting in the Project Calendar.


Certainly, the Actual Duration of a summary task is the value of a proportion, which shows an idea of its progress, but which should not be interpreted as elapsed time or real duration.


You can do the checks in the example above. The Duration 1, Duration 2 column displays the sums of the Duration and Actual Duration of the subtasks, respectively.