U.S. households - distribution of adults, by income tier 2000-2014

Lower-income adults are defined as adults whose annual household income is less than two-thirds of the median, and upper-income households have incomes that are more than double the median.
Middle-income adults are defined as adults whose annual household income is two-thirds to double the national median, after incomes have been adjusted for household size.
Upper-income adults are defined as adults whose annual household income is at least double the national median, after incomes have been adjusted for household size.
For example a single person upper-income household has an annual household income of at least 72,126 U.S. dollars. A family of three would have an income of at least 124,925 U.S. dollars.