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.