Why do young adults coreside with their parents?

Nearly one in every two adults aged 18–29 currently lives with their parents, compared to slightly more than one in four in 1960. The literature focuses on changing labor market conditions and marriage–childbearing delays to account for this shift. Using a Blinder–Oaxaca procedure, we identify a role for housing affordability, measured by market-level median housing rent or price to median household income ratios, as an additional factor in the increase in coresidency since but not before 2000. We endogenize the marriage–childbearing decision with a Heckman selection model and attribute up to a quarter of the observed 9-percentage-point increase in the coresidence share between 2000 and 2021 to a decrease in housing affordability. We find a nonlinear relationship between affordability and coresidence with the relationship strongest in the least affordable metros where affordability constraints might be more binding. Overall, these results show changes in market-level housing affordability are associated with the increase in young adult coresidence over the first two decades of the 21st century.