Although we read and hear many references to the "middle class," there is no official definition of who qualifies as middle class. Many people assume it means a certain level of income, homeownership, and a steady income. A recent study by the Pew Research Center defined middle class in relation to the median U.S. income of $55,000. Pew considered the middle class as households with 2/3 to 2 times the national median income ($55,000), which in 2010 amounted to $35,294 to $105,881 after taxes. Check out pew's middle class calculator for European countries and the U.S.: http://www.pewglobal.org/interactives/european-middle-class-calculator/
As reported in the NYT “Middle class contracted in US over two decades, study finds” by Nelson D. Schwartz, April 24, 2017.