When calculating my GPA in major, should/can I only count courses that are meeting the requirement for major or should I count any course on the same topic and from the same department as my major? For example, if my major is Physics, and I have completed my major with courses A through J, but have also taken the course K after completing all the requirements as an optional course (which does not even count for graduation; a completely optional course), should I count the grade for course K when calculating my major GPA for reporting it on my CV and in applications, or can I not count that one?
If no specific guidance is otherwise provided, I would include additional courses in the same department as the major. The reason for this is that anybody looking over your transcript will assume that, unless the course is clearly marked as a graduate course, it's probably a requirement for your major.
That said, we're also not likely to check your math unless there's a gross error, and we're not likely to sweat a few hundredths of a point difference.
My university calculated my GPA for me. I did not bother to double check their arithmetic.
If your university does not calculate your GPA for you, then just imagine the GPA that you want. No one cares.