* School policies: Individual schools set their own limits on course loads, often based on things like student schedules, teacher availability, and resource constraints. Some schools might have a maximum number of credits or classes per semester or year.
* Student ability and capacity: A student's academic ability and personal workload capacity play a significant role. Some students thrive with a heavier course load, while others do better with a lighter one.
* Graduation requirements: The minimum number of subjects required for graduation is set by the state or local education authority, but that doesn't put an upper limit on how many a student *can* take.
In short, there's no single answer. It's highly context-dependent.