I'm aware of stats, but maybe 12K is barely enough to dispose of for goals - such as going out, or buying presents to others, etc. (Saving rate is around 5%, which is less than 1K/year, that's nowhere near enough for anything. Though allegedly it's not calculated "properly".)
At the median they’re probably not paying for healthcare. Also national well being distribution is a place statistics fail. The median is just slightly more useful than talking about actual income levels and worker benefits. Either society finds a way to house, bathe, feed, and tend the basic healthcare needs of everyone or we really are not better than we were in the 1860s.
The assertion that Americans do not, on average, have money to invest is a false one.