Within the U.S. mortgage industry, different mortgage products are generally defined by how they differ from the types of "conforming" or "agency" mortgages, ones guaranteed by the Government-Sponsored Enterprises (GSEs) Fannie Mae and Freddie Mac.
There are numerous factors that might cause a mortgage not to qualify under the GSEs' traditional lending guidelines even though the borrower's creditworthiness is generally strong. A few of the more important factors are:
In this way, Alt-A loans are "alternatives" to the standard of conforming, GSE-backed mortgages.
Borrower considerations[edit]
An example of a person requesting a Stated Income mortgage is an individual with multiple and varying sources of income that would require an onerous amount of paperwork to document, such as income from self-employment or investments. Note that reduced documentation loans still require that borrowers authorize the lender to order their tax returns at random from the Internal Revenue Service in order to verify the income on the application.
The same documentation features are available under "subprime" guidelines, and similar ones may even be available under agency guidelines. Alt-A and subprime differ in that, generally speaking, an Alt-A borrower would have had a sufficient financial profile to qualify for a "conforming" mortgage, if only it weren't for one of the factors mentioned above, whereas a subprime borrower would suffer from exceptionally weak credit, income or asset characteristics. However, in cases where borrower, property and loan characteristics meet agency guidelines especially well, Fannie's and Freddie's automated preapproval systems generally grant reduced documentation features automatically at no extra cost. More expensive Alt-A or subprime loans are not necessary for strong borrowers to expedite their applications.
Aside from reduced documentation features, Alt-A guidelines usually also offer borrowers greater flexibility than agency guidelines concerning borrower credit scores, income and asset levels. Thus a borrower whose financial profile might not meet agency guidelines for the loan terms requested might still be eligible under Alt-A guidelines.
Property and occupancy considerations[edit]
Aside from the borrower's credit and financial profile, GSE standards are also generally the most stringent regarding how much of a given property type's value or purchase price is permissible to lend on owner-occupied, second ("vacation") and non-owner occupied ("investment") homes, and under what conditions. The combination of these property and occupancy factors with a given borrower's profile can move the loan out of the "prime" category of agency-conforming loans and into less stringent categories such as Alt-A and subprime. For example, Fannie Mae might agree to purchase all loans made by a particular lender on single family second homes in a particular area at a particular maximum LTV for borrowers within given income, asset and credit limits. Borrowers beyond those limits, or those seeking loans above that maximum LTV for second homes, would need to apply for an Alt-A loan. Borrowers still further outside the income, asset and credit limits might need to consider subprime financing—difficult to find as of 2008.
Similar to Alt-A lending, the jumbo and super-jumbo categories generally use an amalgam of agency and Alt-A guidelines for borrower eligibility while allowing larger maximum loan amounts than those permitted by the GSEs (as of 2023, $726,200 for a single family home outside Alaska, Hawaii, Guam and the US Virgin Islands).