Adjustable rate mortgages are to home buyers as carrots are to bunnies - very tempting. The secret to figuring out if an adjustable rate mortgage is a good deal is the rate index used.

Indexes - Setting Rates

Lenders really want your business and are willing to create enticing loan products to get it. Occasionally, lenders will offer adjustable rate mortgages that offer a lot of carrot on the front end, but none on the back end. These loans are typically offered to you with an insanely low initial interest rate, which has you looking at mansions and other structures completely out of your realistic price range. The problem with these loans is the rate rises dramatically after six months or a year when the rate becomes pegged to an index.

Indexes are a unique animal when it comes to the mortgage industry. An index is a calculation of general interest rates charged across a number of financial markets that a bank uses to set a real interest rate on your loan. Common financial markets or products considered in this index include six month certificate deposit rates at local banks, LIBOR, T-Bills and so on. Let's take a closer look.

1. Certificate Deposits - Better known as "CDs", these are the fixed time period investing vehicles you can get at your local bank. You agree to deposit a certain amount for six months and the bank gives you a guaranteed interest rate of return such as three percent.

2. T-Bills - Officially known as Treasury Bills, T-Bills are the credit cards for the federal government. Currently, Uncle Sam owes trillions of dollars on his and pays a certain interest rate on the debit. The interest rate is used by lenders in calculating your ARM rates.

3. Cost of Funds Index - It gets a bit technical, but this index represents the rates being used by banks in Nevada, Arizona and California as an average.

4. LIBOR - Officially known as the London Interbank Offered Rate Index, LIBOR is a popular index upon which to base ARM rates. Now, you are probably wondering what London has to do with the United States real estate market. LIBOR represents the interest rate international banks charge to borrow U.S. dollars on the London currency markets. LIBOR rates move quickly and can result in unstable interest rate moves for your adjustable mortgage.

Why Indexes Matter

Indexes matter because they set the base of the interest rates charged on your loan. Assume you apply for an adjustable rate mortgage based on a LIBOR index. Assume the LIBOR rate is 2.2 percent when you apply. The 2.2 percent is your starting interest rate. If the LIBOR shoots up one percent in eight months, your loan will do the same.

Importantly, the index rate used for your loan is not the interest rate you will pay. Instead, you have to add the banks margin on top of the index rate. Most banks will charge two to three percent on top of the index rate. Using our LIBOR example, the initial interest rate of your loan would be 2.2 percent plus whatever the bank is using as a spread. Obviously, this means you need to closely read the loan documents to figure out how the game is being played!

Dan Lewis is with http://www.gwhomeloans.com - San Diego mortgage brokers providing San Diego home loans. Visit http://www.gwhomeloans.com/services.html to learn more about options on San Diego mortgages from a San Diego mortgage broker company.