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What is an ARM?

Adjustable Rate Mortgage (ARM): A home loan where the interest rate can go up or down during the time you are repaying the loan.

"Some newspaper ads for home loans show surprisingly low rates. Are these loans for real, or is there a catch?"

Some of the ads you see are for adjustable-rate mortgages (ARMs). These loans may have low rates for a short time - maybe only the first year. After that, the rates may be adjusted on a regular basis. This means that the interest rate and the amount of the monthly payment may go up or down.

"Will I know in advance how much my payment may go up?"

With an adjustable-rate mortgage, your future monthly payment is uncertain. Some types of ARMs put a ceiling on your payment increase or interest-rate increase from one period to the next. Virtually all types must put a ceiling on rate increases over the life of the loan.

"Is an ARM the right type of loan for me?"

That depends on your financial situation and the terms of the ARM. ARMs carry risks in periods of rising interest rates, but they can be cheaper over a longer term if interest rates decline. You will be able to answer the question better once you understand more about ARMs.

How ARMs Work:

The Adjustment Period

With most ARMs, the interest rate and monthly payment change every year, every three years, or every five years. However, some ARMs have more frequent rate and payment changes. The period between one rate change and the next is called the "adjustment period." A loan with an adjustment period of one year is called a one-year ARM, and the interest rate can change once every year.

The Index

Most lenders tie ARM interest-rate changes to changes in an "index rate." These indexes usually go up and down with the general movement of interest rates. If the index rate moves up, so does your mortgage rate in most circumstances, and you will probably have to make higher monthly payments. On the other hand, if the index rate goes down, your monthly payment may go down. Lenders base ARM rates on a variety of indexes. Among the most common indexes are the one-, three-, or five-year Treasury securities. Another common index is the national or regional average cost of funds to savings and loan associations. A few lenders use their own cost of funds as an index, which gives them more control than using other indexes. You should ask what index will be used and how often it changes. Also ask how it has fluctuated in the past and where it is published.

The Margin

To determine the interest rate on an ARM, lenders add to the index rate a few percentage points, called the "margin." The amount of the margin may differ from one lender to another, but it is usually constant over the life of the loan.

Index rate + margin = ARM interest rate


Some lenders offer initial ARM rates that are lower than their "standard" ARM rates (that is, lower than the sum of the index and the margin). Such rates, called discounted rates, are often combined with large initial loan fees ("points") and with much higher rates after the discount expires. Very large discounts are often arranged by the seller. The seller pays an amount to the lender so that the lender can give you a lower rate and lower payments early in the mortgage term. This arrangement is referred to as a "seller buydown." The seller may increase the sales price of the home to cover the cost of the buydown. A lender may use a low initial rate to decide whether to approve your loan, based on your ability to afford it. You should be careful to consider whether you will be able to afford payments in later years when the discount expires and the rate is adjusted.


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