A conventional loan is a mortgage that is not guaranteed or insured by any government agency, including the Federal Housing Administration (FHA), the Farmers Home Administration (FmHA) and the Department of Veterans Affairs (VA). It is typically fixed in its terms and rate.
Conventional loans held by mortgage lenders on their own books are called “portfolio” loans. Because lenders can set their own guidelines for these loans and do not sell them to investors, these products may have features that other mortgages do not. For example, a portfolio lender might allow a borrower to use investments like stocks and bonds as security for a mortgage for which she would not otherwise qualify.
Conventional home loans marketed to borrowers with low credit scores are called sub-prime mortgages. They typically come with high interest rates and fees. The government has created special rules covering the sale of such products, but they are not government-backed — they are conventional loans.