Who can use this capability
The sheet's Owner and Admins can modify the sheet Project Settings.
Parent rollup functionality
Start Date, End Date, Duration, and % Complete for parent rows
The Start Date for a parent is the earliest start date from all of its child rows. Similarly, the End Date is the last end date from all its child rows.
The Duration on the parent reflects the number of working days between the Start Date and End Date in that row. It provides a full time span, from the earliest subtask to the latest, as opposed to a sum of their durations.
The % Complete on the parent row calculates a weighted percentage based on both the Duration and % Complete entered on each child row. In this way, completing child rows with shorter durations does not affect the parent row % Complete as much as completing a longer duration child row.
The parent row rollup includes only subtasks with a given Duration and a % Complete value.
You cannot edit parent rows with enabled dependencies in the Start Date, End Date, Duration, and % Complete columns. To use your own calculations, you can disable the Dependency functionality on the sheet or create your desired formula in a columns not used in the dependency functionality.
You cannot use custom formulas to change the display or bars in the Gantt chart.
Parent rows in dependency-enabled sheets always have a grey background color in the Gantt and Calendar views.
Parent rows always reflect duration in partial working days, even if you use other formats to show duration for the child rows.
Parent rows do not calculate % Complete rollups when any of their child rows contains milestones (duration = 0).