Why has living at home become so voguish among millennials? Blame high housing costs. Blame declining marriage rates. And, also, blame the parents.

This was supposed to be a temporary phenomenon, a short-term rush for shelter set off by the financial crisis of 2007-2009. But it just keeps going. Every year, more and more 25-to-34-year-olds turn up in their parents’ houses, right through to 2016.

You can’t blame the economy — not anymore. Young adults continue to move back home with their parents, even though the United States has enjoyed seven straight years of economic growth, pushing the unemployment rate below 5 percent.


Start with the housing costs, which have become a major impediment to independence. A recent analysis from the Federal Reserve Bank of Boston found that housing really is less affordable for today’s young adults than it was for their peers 20 years ago — a key reason they’ve been slower to move out.

Even when millennials do move out, they’re more likely to rent than buy. And that matters too, because it means that when times get tough it’s easier for them to pack up their things and return to their childhood rooms.

Still, there’s more to this story than housing costs — and other economic factors like student debt. Even though it’s true that today’s 25-to-34-year-olds have faced a particularly unfriendly economic landscape for much of their early adulthood, that alone can’t explain their peerless penchant for moving back home.

Today’s young adults are also different from their predecessors: Generation X and baby boomers. They’re more racially diverse, for one thing. And they also have a different worldview and different preferences.

Take marriage. Millennials tend to marry later, and less frequently, than earlier generations. Only about a third of them have tied the knot, according to the Pew Research Center. That compares with 44 percent of Generation Xers and over half of boomers (when they were that young).


Once you account for this trend, the whole “living at home” issue seems to disappear. Married 25-to-34-year-olds continue to set up independent households at roughly the same rate they always have. Unmarried folks have always been less keen to leave. It’s just that today there are a lot more of them.

The trouble with this “blame low marriage rates” approach is that it involves a kind of chicken-and-egg problem (endogeneity, for you economists). Is it that young people are living with parents because they’re not getting married? Or are they not getting married because they’re stuck at home? It’s hard to know, and yet the answer matters a lot.

There is one last possibility. Maybe young adults are staying at home because their parents — and society at large — have simply grown more tolerant of the idea. Once upon a time, living at home carried a kind of stigma; it was considered a sign that you weren’t progressing through life at the proper pace. But perhaps that’s lifting.

The Boston Fed found some suggestive evidence in its analysis. Among other things, a growing number of Americans now say it’s OK for older people to share a home with grown children.

As to why this stigma might be fading, there are a lot of potential reasons. Houses have gotten bigger, making the empty nest feel emptier and creating more room for returning children. Also, young people aren’t moving around the country as much as they used to, which means they tend to have parents nearby when they need support.


Plus, everyone else is doing it. Quite often, when behaviors become more common they start to seem more acceptable.

Does this mean we have reached a new normal, and that the number of young people living at home may continue to rise? Perhaps. But what goes up can also come down. For instance, if housing gets more affordable, that would open a new path to independent living.

And we have seen turnarounds before. The 1940s and 1950s witnessed a dramatic decline in the number of young Americans living with parents. Unfortunately, that was precipitated by a devastating world war and the subsequent surge in marriage that created the baby boomers. Hopefully this time we won’t need anything quite so world-historical.

Shutterstock / Andy Dean Photography

Evan Horowitz digs through data to find information that illuminates the policy issues facing Massachusetts and the United States. He can be reached at evan.horowitz@globe.com. Follow him on Twitter @GlobeHorowitz