Around half of new build retirement homes sold during a 10-year period were later re-sold at a loss, according to exclusive research for the BBC.
The research by the Elderly Accommodation Counsel charity found falls in value could be more than 50%.
It looked at thousands of Land Registry records for resale details of homes built between 1998 and 2012.
The charity found many properties built after 2002 had underperformed the general property market.
Adam Hillier of the Elderly Accommodation Counsel (EAC), which advises people considering retirement housing, called the scale of the falls “startling”.