A conventional mortgage is a type of mortgage in which the underlying terms and conditions meet the funding criteria of Fannie Mae and Freddie Mac. About 35-50% of mortgages, depending on market conditions and consumer trends, are conventional mortgages. In other words, Fannie Mae and Freddie Mac guarantee or purchase 35-50% of all mortgages. Conventional mortgages may be fixed-rate or adjustable-rate mortgages.
The secondary market for conventional mortgages is extremely large and liquid. Most conventional mortgages are packaged into pass-through mortgage-backed securities, which trade in a well-established forward market known as the mortgage TBA (to be announced) market. Many conventional pass-through securities are further securitized into collateralized mortgage obligations (CMOs).