Year-over-year (YoY) price change compares median sale price in a given month against the same month one year prior. It is the cleanest way to measure real price momentum because it automatically removes seasonal effects that distort month-over-month comparisons.
How ZipMarketData Reports YoY Change
The /market-stats endpoint returns yoy_price_change as a percentage for each ZIP code — positive means prices are higher than 12 months ago, negative means they've declined. Values are derived from Redfin's trailing 12-month Redfin market data.
Interpreting YoY Ranges
| YoY Change | Market Signal |
|---|---|
| > +8% | Overheating — watch for affordability ceiling |
| +3% to +8% | Healthy appreciation — strong demand, supply constrained |
| 0% to +3% | Stable market — inflation-pace growth |
| −3% to 0% | Softening — watch inventory and DOM trends |
| < −3% | Declining market — verify employment/population drivers |
Combining YoY with DOM for Market Classification
The most reliable market signal combines YoY price change with days-on-market: a ZIP code with positive YoY and sub-30-day DOM is structurally strong. A ZIP code with falling prices and rising DOM is in genuine distress. Markets in between require more nuanced analysis of supply-side drivers.