“Most studies define the middle class relative to the national median, which makes the dividing line between haves and have-nots rise automatically as the country gets richer. Rose and Winship instead use a benchmark of fixed purchasing power, so that if real incomes (those adjusted for inflation) rise, more people are shown moving into—or beyond—the middle class in a meaningful sense.
Under this approach, the “core” of the middle class does indeed shrink modestly. But crucially, the middle class shrinks because people are moving up the income ladder, not because they’re falling down. Since 1979, the share of Americans in the upper-middle class has roughly tripled—from about 10 percent to 31 percent—while shares of those considered lower middle class or poor fell substantially.”
https://reason.com/2026/01/15/yes-the-middle-class-is-shrinking-because-its-moving-up