What the FHFA house price index measures
FHFA describes its index as a broad measure of the movement of single-family house prices: a weighted, repeat-sales index that measures average price changes in repeat sales or refinancings on the same properties. The data come from mortgages bought or guaranteed by Fannie Mae and Freddie Mac since 1975. This site shows those indexes as FHFA publishes them.
Repeat sales
Rather than averaging the prices of whatever homes happen to sell in a period, a repeat-sales index looks at homes that have transacted at least twice and measures how much each one's price changed between its transactions. Pairing a home with itself controls for the mix of homes selling: a quarter with many large-home sales does not push the index up on its own. The method cannot see homes that never resell, and it relies on the same home being broadly the same home over time; major renovations and neglect both leak into the measure.
Purchase-only and all-transactions
The purchase-only index uses sales prices only. The all-transactions index adds appraisal values from refinance mortgages, which gives far more observations and allows indexes for smaller areas, at the cost of including appraisals rather than agreed prices. FHFA publishes both quarterly for the nation, divisions, states and metropolitan areas; the annual county, ZIP code and CBSA indexes are all-transactions. This site uses all-transactions everywhere for comparability and shows the purchase-only state series for reference.
Conforming mortgages
Only homes financed with mortgages sold to or guaranteed by Fannie Mae or Freddie Mac enter the sample. Homes bought with cash, with jumbo loans above the conforming limit, or with FHA or VA loans are not in the standard index (FHFA's expanded-data index adds some of these). In expensive areas the sample under-represents the top of the market.
The base period
Each index is set to 100 in its base period, the first year (or quarter) the area has enough transactions; a value of 250 means prices in repeat transactions are two and a half times their base-period level. Because base years differ by area, index levels are not comparable across areas; changes over the same span are. That is why every comparison on this site is a percentage change over identical years, and why the reference line on each chart is rebased to the area's own start.
Developmental indexes
FHFA labels the annual county, ZIP code, three-digit ZIP, CBSA and tract indexes developmental. They are calibrated on the same appraisal and sales data, but small areas have small samples: FHFA does not report a value where recording has not started, reports a missing value where the sample is too thin, and revises the series as new data arrive. A ZIP code index that stops before 2025 usually reflects too few transactions in the later years. Pages on this site carry a "developmental" label where these indexes are used.
Not seasonally adjusted
The annual indexes are calendar-year values. The quarterly all-transactions index shown on state and metro pages is the not-seasonally-adjusted series; quarter-to-quarter changes carry a seasonal pattern, which is why the site emphasises the change over four quarters.
What the index is not
- It is not a dollar value. An index of 300 says nothing about what any home costs.
- It is not a median price. Medians move with the mix of homes sold; the index is built to remove that.
- It is not a forecast. It records what has happened to prices in the sample.
FHFA publishes its technical documentation alongside the datasets at fhfa.gov/data/hpi.