Social Explorer; Federal Housing Finance Agency House Price Index (HPI).
House Price Index Technical Documentation
5. How is the HPI updated?
Each month, Fannie Mae and Freddie Mac provide FHFA with information on their most recent mortgage transactions. These data are combined with the data from previous periods to establish price differentials on properties where more than one mortgage transaction has occurred. The data are merged, creating an updated historical database that is then used to estimate the HPI.