How to Update % Complete
As a task assignee works on a task, they should update the «% Complete» value. By specifying a percentage of completion between 0 (for a task that hasn't started) and 100 (for a task that is finished), you can compare planned progress to actual progress.
To update the completed percentage:
1. Open the task by double-clicking on it.
2. Go to the «% Complete» box.
3. Click the arrow buttons to increase or decrease the «% Complete» value (the increment value is 1 percent) or type your own value.
4. When finished, click «Save» in the Ribbon.