A growing Boston has added tens of thousands of households in the last 25 years, but the city's middle class is shrinking overall, a new report spotlights.

From 1990 to 2014, the number of high-income households in Boston jumped by 43,000 and the number of low-income households increased by 30,000, but the tally of households at the middle of the income distribution fell by 15,000, according to a Boston Foundation analysis of census data, out Wednesday.

(Courtesy of the Boston Foundation)

The foundation's figures mirror findings on the national level, showing a decline in the share of middle-class Americans.

The report says the growth in the share of high-income households reflects Boston's addition of higher-wage jobs, like in health care and informational technology sectors — and that high housing costs play a key role, as well.

"[A]s demand to live in Boston dramatically outpaces the production of new

housing, higher-income households are the only ones equipped to stay and pay market rates," the analysis states.

The Boston Foundation has advocated for an increase in housing production in the area, as a way to moderate housing costs. A new coalition of 15 municipal leaders that includes Boston Mayor Marty Walsh just last week called for the creation of 185,000 new housing units by 2030.

The report — titled "Boston's Booming ... But For Whom?" — collects data from a number of sources on a variety of economic indicators for the city and region, including income inequality, poverty, economic mobility and home ownership.

(Courtesy of the Boston Foundation)

As Boston Foundation President and CEO Paul Grogan writes in its introduction, "[t]here is some encouraging news" in the analysis, such as Boston's overall prosperity and relative strength in economic mobility, compared with peer cities.

Nevertheless, the report focuses on the area's inequities along lines of race and class.

"Finding ways to better leverage our economic boom for the benefit of all residents and all neighborhoods has become the central challenge of our time," it concludes.

The analysis adds another sobering statistic to Boston's issues with housing affordability: In just 20 of the city's 170 census tracts, households earning the median income can comfortably afford the area's median rent. (In this report, such affordable rent is defined as 30 percent or less of a household's income.)

"[I]t’s striking," the analysis states, "that wide swaths of several neighborhoods that were once thought of as affordable actually are not. ... In 2018, every single census tract in Dorchester, Roxbury and Mattapan is unaffordable to households earning median incomes." Here's a map view of that finding:

(Courtesy of the Boston Foundation)

For all of Boston, median monthly rent is $2,613, per the report — a total that's 51 percent of median household income in the city.

The Walsh administration recently announced a new, higher housing production target, saying it is outpacing its original goal, which was announced in 2014.

The focus of the housing plan, Walsh told reporters two weeks ago, is to "make sure that people can stay in the city of Boston."

The city has said it expects to have about 100,000 more residents by 2030.