So it is a case of “Upper Class” depends solely on annual “household income” and has nothing to do with education level, upbringing, or belonging to the “nobility” by birth?
To be in the “Lower Class” just means your annual household income fall under a certain threshold, which is not much above the official “Federal Poverty Level” for a family of three (US$ 23,033 in 2022)
Anybody in between belong to the “Middle Class”, which Paw Centre define as: