Interest rates are based on the one-year LIBOR index plus a margin.
Although many mortgage companies base their interest rates on the Federal Prime Rate, Chase Home Finance bases their mortgage interest rates on the London Interbank Offered Rate, also known as the LIBOR.
Some lenders tie their interest rates closely to an index such as the Prime Rate or the Libor plus a predetermined margin, but the choice is ultimately up to the lender to decide what interest rate to charge.
Lenders commonly offer ARMs that are either attached to the Prime Rate or the LIBOR.
The LIBOR and the Prime Rate are often similar, but there is usually a difference between the two.