How To Update % Complete
As a task assignee works on a task, they should update the Percent 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 Percent Complete value (the increment value is 25 percent) or type your own value.
4. Click the Save button.