Demand data (DOM, sale-to-list ratio) gets most of the attention, but supply data — active listings, new listings, and months of inventory — drives the structural story. A market with rising demand but rapidly rising supply will soften regardless of how strong buyers appear.

Active Listings vs New Listings

Active listings is the total inventory available at a point in time. New listings measures freshly added supply in a period. If new listings are flooding in faster than homes are going under contract, the active count rises and the market shifts toward buyers.

Months of Supply

Months of Supply = Active Listings / Monthly Closed Sales < 3 months → Seller's market 3–6 months → Balanced market > 6 months → Buyer's market

ZIP Code Inventory via API

ZipMarketData's /market-stats endpoint returns active_listings count per ZIP code. Pair this with sales_count from /price-history to compute months of supply for any market you're analysing.

NoteInventory data from Redfin's public tracker represents a monthly snapshot. Weekly fluctuations aren't captured, but monthly trend lines are sufficient for investment screening purposes.

Inventory Trends as a Leading Indicator

Inventory changes tend to lead price changes by 2–4 months. Falling inventory in a market that has been cooling often signals the bottom before prices stabilise and begin recovering — a useful early-entry signal for patient investors.