What level of housing inventory signals home price declines ahead?
Core argument: The authors estimate an inventory threshold of 5.0 months, above which months of supply has a clearly negative relationship with year-over-year home price changes 9 months later, while below it the relationship is weak.
We answer two questions: Is there a specific level of inventory that reliably signals price declines? What’s the lag between rising supply and falling prices? We estimate the inventory threshold at 5.0 months. Below that level, inventory has only a weak relationship with year-over-year home price changes. But above it, the relationship becomes more clearly negative, signaling price declines 9 months in the future. Based on the model coefficients, we calculate that the predicted change in home prices turns negative at 5.81 months of inventory. The fit is unusually strong: our best-performing model—a 9-month lag with a 5.0-month threshold—yields an adjusted R² of 0.75, indicating that it explains a substantial share of the variation in home price growth. We can extract a simple rule of thumb from these results: once inventory is above 5 months, each additional month of inventory suggests home prices will be about 3% lower than they would otherwise be, 9 months down the road.




