In existing mortgage contracts borrowers pay a series of
cash flows. Equivalently, the mortgage interest rate is the sum
of a bond interest rate, servicing fee, and guarantee fee. The
mortgage interest rate depends on the credit quality of the
applicant, particularly with automated underwriting systems.
These computerized systems immediately accept or reject
applicants. Lower-quality borrowers face higher interest rates,
partly because they must leave markets with either direct or
indirect federal government guarantees. The borrower pays
for mortgage insurance, tiered by loan-to-value ratio.