An interest-only loan is a loan in which the borrower pays only the interest for some or all of the term, with the principal balance unchanged during the interest-only period. At the end of the interest-only term the borrower must renegotiate another interest-only mortgage, pay the principal, or, if previously agreed, convert the loan to a principal-and-interest payment (amortizing) loan at the borrower’s option.
Interest-only securities are sometimes generated artificially from structured securities, particularly CMOs. A pool of securities (typically mortgages) is created, and divided into tranches; the cash received from the underlying debts are spread through the tranches according to predefined rules. An Interest-only (IO) security is one type of tranche that can be created, it is generally created in tandem with a principal-only (PO) tranche. These tranches will cater to two particular types of investors, depending on whether the investors are trying to increase their current yield (which they can get from an IO), or trying to reduce their exposure to prepayments of the loans (which they can get from a PO). The investment returns on IOs and POs depend heavily on mortgage prepayment rates and permit investors to benefit from different prepayment expectations.
Many U.S. markets saw home values increase by as much as four times in a five-year span in the early 2000s. Interest-only loans helped homeowners afford more home and earn more appreciation during this time period. However, interest-only loans contributed greatly to creating the subsequent housing bubble situation, because variable-rate borrowers could not afford the fully indexed rate. Interest-only loans are disadvantaged for borrowers when housing prices drop, making the mortgage larger than the value of the house.
