Any activity in a Moodle course can be designated as extra credit and calculated accordingly in the gradebook.
Marking an individual item as extra credit will remove the score of that item from the category or course total. The score a student receives on the extra credit item will be added to their grade after other totals have been calculated.
WARNING: Do NOT set up an entire Category as extra credit and set the Category weighting at 0. A Category with a weighting of 0 will result in nothing within that Category being calculated into the student's final grade.
Note: To give students extra credit on an activity outside the Moodle course site, see Add a Grade Item to the Gradebook to create the extra credit item before following the directions below.
Setting up an activity as extra credit in the gradebook
Go to the course homepage.
Find the Administration block:
Click Gradebook setup (Moodle 3.0, 3.2).
Find the activity that should be graded as extra credit.
Click Edit, then Edit settings for that activity.
Expand the Parent category to see the options if necessary (may need to click Show more... to see the extra credit option.
Check the Extra Credit checkbox.
Scroll down and click Save changes.
The value for that activity in the Max grade column will now have a + symbol, indicating extra credit value.
Note: The student view of grades has no indicator that the particular score is extra credit. Consider putting the words Extra Credit somewhere within the activity title to be clear to students.