The Remaining Tasks field shows the total number of scheduled subtask that remain to be completed for a summary task on a given day. If the project summary task is displayed, the Remaining Tasks field shows the total number of scheduled tasks and subtasks that remain to be completed on a given day for the entire project.
Data Type Number
Entry Type Calculated
How Calculated To calculate the Remaining Tasks field, Project totals the number of subtasks under a summary task, and then subtracts the number of subtasks that have a finish date on that day or earlier.
To calculate the Remaining Tasks field for the project summary task, Project totals the number of scheduled tasks and subtasks for the entire project, and then subtracts the number of subtasks and tasks that have a finish date on that day or earlier. Note: Project includes subtasks and regular tasks in this calculation, but it does not include actual summary tasks (a task that includes subtasks).
Best Uses Create summary tasks that contain one or more subtasks. Add the Remaining Tasks field to the timephased portion of the Task Usage view when you want to display how many scheduled subtasks remain to be completed on a given day for a summary task.
Example The "Write proposal" summary task has 3 subtasks: “Write”, “Edit,” and “Revise.”
The “Write” task is scheduled for days 1 and 2.
The “Edit” task is scheduled for day 3.
“Revise” is scheduled for days 4 and 5.
You add the Remaining Tasks field to the timephased portion of the Task Usage view. At day 1, it is 3. At day 2, it is 2.
At day 3, it is 1. At day 4, it is 1. At day 5, it is 0.
Remarks

Subtasks will always display a 1 in the Remaining Tasks field before the finish date, and a 0 on the finish date.

You can turn on the project summary task on the Advanced tab of the Project Options dialog box.