How ARMs work: the basic features

What is an ARM?

An adjustable-rate mortgage differs from a fixed-rate mortgage in many ways. Most importantly, with a fixed rate mortgage, the interest rate stays the same during the life of the loan. With an ARM, the interest rate changes periodically, usually in relation to an index, and payments may go up or down accordingly.

To compare two ARMs, or to compare an ARM with a fixed-rate mortgage, you need to know about indexes, margins, discounts, caps on rates and payments, negative amortization, payment options, and recasting (recalculating) your loan. You need to consider the maximum amount your monthly payment could increase. Most importantly, you need to know what might happen to your monthly mortgage payment in relation to your future ability to afford higher payments.

Lenders generally charge lower initial interest rates for ARMs than for fixed-rate mortgages. At first, this makes the ARM easier on your pocketbook than would be a fixed-rate mortgage for the same loan amount. Moreover, your ARM could be less expensive over a long period than a fixed-rate mortgage—for example, if interest rates remain steady or move lower.

Against these advantages, you have to weigh the risk that an increase in interest rates would lead to higher monthly payments in the future. It’s a trade-off —you get a lower initial rate with an ARM in exchange for assuming more risk over the long run.

Here are some questions you need to consider:

  • Is my income enough—or likely to raise enough—to cover higher mortgage payments if interest rates go up?
  • Will I be taking on other sizable debts, such as a loan for a car or school tuition, in the near future?
  • How long do I plan to own this home? (If you plan to sell soon, rising interest rates may not pose the problem they do if you plan to own the house for a long time.)
  • Do I plan to make any additional payments or pay the loan off early?

Lenders and Brokers

Mortgage loans are offered by many kinds of lenders—such as banks, mortgage companies, and credit unions. You can also get a loan through a mortgage broker. Brokers “arrange” loans; in other words, they find a lender for you. Brokers generally take your application and contact several lenders, but keep in mind that brokers are not required to find the best deal for you unless they have contracted with you to act as your agent.

How ARMs Work: The Basic Features

Initial rate and payment

The initial rate and payment amount on an ARM will remain in effect for a limited period—ranging from just 1 month to 5 years or more. For some ARMs, the initial rate and payment can vary greatly from the rates and payments later in the loan term. Even if interest rates are stable, your rates and payments could change a lot. If lenders or brokers quote the initial rate and payment on a loan, ask them for the annual percentage rate (APR). If the APR is significantly higher than the initial rate, then it is likely that your rate and payments will be a lot higher when the loan adjusts, even if general interest rates remain the same.

The Adjustment Period

With most ARMs, the interest rate and monthly payment change every month, quarter, year, 3 years, or 5 years. The period between rate changes is called the adjustment period. For example, a loan with an adjustment period of 1 year is called a 1-year ARM, and the interest rate and payment can change once every year; a loan with a 3-year adjustment period is called a 3-year ARM.

Loan Descriptions

Lenders must give you written information on each type of ARM loan you are interested in. The information must include the terms and conditions for each loan, including information about the index and margin, how your rate will be calculated, how often your rate can change, limits on changes (or caps), an example of how high your monthly payment might go, and other ARM features such as negative amortization.

The Index

The interest rate on an ARM is made up of two parts: the index and the margin. The index is a measure of interest rates generally, and the margin is an extra amount that the lender adds. Your payments will be affected by any caps, or limits, on how high or low your rate can go. If the index rate moves up, so does your interest 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 could go down. Not all ARMs adjust downward, however—be sure to read the information for the loan you are considering.

Lenders base ARM rates on a variety of indexes. Among the most common indexes are the rates on 1-year constant-maturity Treasury (CMT) securities, the Cost of Funds Index (COFI), and the London Interbank Offered Rate (LIBOR). A few lenders use their own cost of funds as an index, rather than using other indexes. You should ask what index will be used, how it has fluctuated in the past, and where it is published—you can find a lot of this information in major newspapers and on the Internet.

The Margin

To set the interest rate on an ARM, lenders add a few percentage points to the index rate, 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. The fully indexed rate is equal to the margin plus the index. If the initial rate on the loan is less than the fully indexed rate, it is called a discounted index rate. For example, if the lender uses an index that currently is 4% and adds a 3% margin, the fully indexed rate would be

Index 4% + Margin 3% = Fully indexed rate 7%

If the index on this loan rose to 5%, the fully indexed rate would be 8% (5% + 3%). If the index fell to 2%, the fully indexed rate would be 5% (2% + 3%).

Some lenders base the amount of the margin on your credit record— the better your credit, the lower the margin they add—and the lower the interest you will have to pay on your mortgage. In comparing ARMs, look at both the index and margin for each program.

No-Doc/Low-Doc Loans

When you apply for a loan, lenders usually require documents to prove that your income is high enough to repay the loan. For example, a lender might ask to see copies of your most recent pay stubs, income tax filings, and bank account statements. In a “no-doc” or “low-doc” loan, the lender doesn’t require you to bring proof of your income, but you will usually have to pay a higher interest rate or extra fees to get the loan. Lenders generally charge more for no-doc/low-doc loans.

Interest-Rate Caps

An interest-rate cap places a limit on the amount your interest rate can increase. Interest caps come in two versions:

  • A periodic adjustment cap, which limits the amount the interest rate can adjust up or down from one adjustment period to the next after the first adjustment, and
  • A lifetime cap, which limits the interest-rate increase over the life of the loan. By law, virtually all ARMs must have a lifetime cap.

Periodic adjustment caps

Some ARMs allow a larger rate change at the first adjustment and then apply a periodic adjustment cap to all future adjustments. A drop in interest rates does not always lead to a drop in your monthly payments. With some ARMs that have interest-rate caps, the cap may hold your rate and payment below what it would have been if the change in the index rate had been fully applied. The increase in the interest that was not imposed because of the rate cap might carry over to future rate adjustments. This is called carryover. So, at the next adjustment date, your payment might increase even though the index rate has stayed the same or declined.

In general, the rate on your loan can go up at any scheduled adjustment date when the lender’s standard ARM rate (the index plus the margin) is higher than the rate you are paying before that adjustment.

Payment Caps

In addition to interest-rate caps, many ARMs—including payment-option ARMs—limit, or cap, the amount your monthly payment may increase at the time of each adjustment. Some ARMs with payment caps do not have periodic interest rate caps. In addition, as explained below, most payment-option ARMs have a built-in recalculation period, usually every 5 years. At that point, your payment will be recalculated (lenders use the term recast) based on the remaining term of the loan. If you have a 30-year loan and you are at the end of year 5, your payment will be recalculated for the remaining 25 years. The payment cap does not apply to this adjustment. If your loan balance has increased, or if interest rates have risen faster than your payments, your payments could go up a lot.

Types of ARMs

Hybrid ARMs

Hybrid ARMs often are advertised as 3/1 or 5/1 ARMs—you might also see ads for 7/1 or 10/1 ARMs. These loans are a mix— or a hybrid—of a fixed-rate period and an adjustable-rate period. The interest rate is fixed for the first few years of these loans—for example, for 5 years in a 5/1 ARM. After that, the rate may adjust annually (the 1 in the 5/1 example) until the loan is paid off. In the case of 3/1 or 5/1 ARMs:

  • the first number tells you how long the fixed interest-rate period will be, and
  • the second number tells you how often the rate will adjust after the initial period.

You may also see ads for 2/28 or 3/27 ARMs—the first number tells you how many years the fixed interest rate period will be, and the second number tells you the number of years the rates on the loan will be adjustable. Some 2/28 and 3/27 mortgages adjust every 6 months, not annually.

Interest-only (I-O) ARMs

An interest-only (I-O) ARM payment plan allows you to pay only the interest for a specified number of years, typically for 3 to 10 years. This allows you to have smaller monthly payments for a period. After that, your monthly payment will increase—even if interest rates stay the same—because you must start paying back the principal as well as the interest each month. For some I-O loans, the interest rate adjusts during the I-O period as well.

Payment-option ARMs

A payment-option ARM is an adjustable-rate mortgage that allows you to choose among several payment options each month. The options typically include the following:

  • a traditional payment of principal and interest, which reduces the amount you owe on your mortgage. These payments are based on a set loan term, such as a 15-, 30-, or 40-year payment schedule.
  • an interest-only payment, which pays the interest but does not reduce the amount you owe on your mortgage as you make your payments.
  • a minimum (or limited) payment that may be less than the amount of interest due that month and may not reduce the amount you owe on your mortgage. If you choose this option, the amount of any interest you do not pay will be added to the principal of the loan, increasing the amount you owe and your future monthly payments, and increasing the amount of interest you will pay over the life of the loan. In addition, if you pay only the minimum payment in the last few years of the loan, you may owe a larger payment at the end of the loan term, called a balloon payment.

The interest rate on a payment-option ARM is typically very low for the first few months (for example, 2% for the first 1 to 3 months). After that, the interest rate usually rises to a rate closer to that of other mortgage loans. Your payments during the first year are based on the initial low rate, meaning that if you only make the minimum payment each month, it will not reduce the amount you owe and it may not cover the interest due. The unpaid interest is added to the amount you owe on the mortgage, and your loan balance increases. This is called negative amortization. This means that even after making many payments, you could owe more than you did at the beginning of the loan. Also, as interest rates go up, your payments are likely to go up.

Payment-option ARMs have a built-in recalculation period, usually every 5 years. At this point, your payment will be recalculated (or “recast”) based on the remaining term of the loan. If you have a 30-year loan and you are at the end of year 5, your payment will be recalculated for the remaining 25 years. If your loan balance has increased because you have made only minimum payments, or if interest rates have risen faster than your payments, your payments will increase each time your loan is recast. At each recast, your new minimum payment will be a fully amortizing payment and any payment cap will not apply. This means that your monthly payment can increase a lot at each recast.

Lenders may recalculate your loan payments before the recast period if the amount of principal you owe grows beyond a set limit, say 110% or 125% of your original mortgage amount. For example, suppose you made only minimum payments on your $200,000 mortgage and had any unpaid interest added to your balance. If the balance grew to $250,000 (125% of $200,000), your lender would recalculate your payments so that you would pay off the loan over the remaining term. It is likely that your payments would go up substantially.

Consumer cautions

Discounted interest rates

Many lenders offer more than one type of ARM. Some lenders offer an ARM with an initial rate that is lower than their fully indexed ARM rate (that is, lower than the sum of the index plus the margin). Such rate —called discounted rates, start rates, or teaser rates—are often combined with large initial loan fees, sometimes called points, and with higher rates, after the initial discounted rate expires.

Your lender or broker may offer you a choice of loans that may include “discount points” or a “discount fee.” You may choose to pay these points or fees in return for a lower interest rate. But keep in mind that the lower interest rate may only last until the first adjustment.

If a lender offers you a loan with a discount rate, don’t assume that means that the loan is a good one for you. You should carefully consider whether you will be able to afford higher payments in later years when the discount expires and the rate is adjusted. Here is an example of how a discounted initial rate might work. Let’s assume that the lender’s fully indexed 1-year ARM rate (index rate plus margin) is currently 6%; the monthly payment for the first year would be $1,199.10. But your lender is offering an ARM with a discounted initial rate of 4% for the first year. With the 4% rate, your first-year’s monthly payment would be $954.83.

With a discounted ARM, your initial payment will probably remain at $954.83 for only a limited time—and any savings during the discount period may be offset by higher payments over the remaining life of the mortgage. If you are considering a discount ARM, be sure to compare future payments with those for a fully indexed ARM. In fact, if you buy a home or refinance using a deeply discounted initial rate, you run the risk of payment shock, negative amortization, or prepayment penalties or conversion fees.

Negative amortization—When you owe more money than you borrowed

Negative amortization means that the amount you owe increases even when you make all your required payments on time. It occurs whenever your monthly mortgage payments are not large enough to pay all of the interest due on your mortgage—meaning the unpaid interest is added to the principal on your mortgage and you will owe more than you originally borrowed. This can happen because you are making only minimum payments on a payment option mortgage or because your loan has a payment cap.

For example, suppose you have a $200,000, 30-year payment option ARM with a 2% rate for the first 3 months and a 6% rate for the remaining 9 months of the year. Your minimum payment for the year is $739.24, as shown in the previous graph. However, once the 6% rate is applied to your loan balance, you are no longer covering the interest costs. If you continue to make minimum payments on this loan, your loan balance at the end of the first year of your mortgage would be $201,118—or $1,118 more than you originally borrowed.

Because payment caps limit only the amount of payment increases, and not interest-rate increases, payments sometimes do not cover all the interest due on your loan. This means that the unpaid interest is automatically added to your debt, and interest may be charged on that amount. You might owe the lender more later in the loan term than you did at the beginning. A payment cap limits the increase in your monthly payment by deferring some of the interest. Eventually, you would have to repay the higher remaining loan balance at the interest rate then in effect. When this happens, there may be a substantial increase in your monthly payment.

Some mortgages include a cap on negative amortization. The cap typically limits the total amount you can owe to 110% to 125% of the original loan amount. When you reach that point, the lender will set the monthly payment amounts to fully repay the loan over the remaining term. Your payment cap will not apply, and your payments could be substantially higher. You may limit negative amortization by voluntarily increasing your monthly payment. Be sure you know whether the ARM you are considering can have negative amortization.

Prepayment penalties and conversion

If you get an ARM, you may decide later that you don’t want to risk any increases in the interest rate and payment amount. When you are considering an ARM, ask for information about any extra fees you would have to pay if you pay off the loan early by refinancing or selling your home and whether you would be able to convert your ARM to a fixed-rate mortgage.

Prepayment penalties

Some ARMs, including interest-only and payment-option ARMs, may require you to pay special fees or penalties if you refinance or pay off the ARM early (usually within the first 3 to 5 years of the loan). Some loans have hard prepayment penalties, meaning that you will pay an extra fee or penalty if you pay off the loan during the penalty period for any reason (because you refinance or sell your home, for example). Other loans have soft prepayment penalties, meaning that you will pay an extra fee or penalty only if you refinance the loan, but you will not pay a penalty if you sell your home. Also, some loans may have prepayment penalties even if you make only a partial prepayment.

Prepayment penalties can be several thousand dollars. For example, suppose you have a 3/1 ARM with an initial rate of 6%. At the end of year 2, you decide to refinance and pay off your original loan. At the time of refinancing, your balance is $194,936. If your loan has a prepayment penalty of 6 months’ interest on the remaining balance, you would owe about $5,850.

Sometimes there is a trade-off between having a prepayment penalty and having lower origination fees or lower interest rates. The lender may be willing to reduce or eliminate a prepayment penalty based on the amount you pay in loan fees or on the interest rate in the loan contract.

If you have a hybrid ARM—such as a 2/28 or 3/27 ARM—be sure to compare the prepayment penalty period with the ARM’s first adjustment period. For example, if you have a 2/28 ARM that has a rate and payment adjustment after the second year, but the prepayment penalty is in effect for the first 5 years of the loan, it may be costly to refinance when the first adjustment is made.

Most mortgages let you make additional principal payments with your monthly payment. In most cases, this is not considered prepayment, and there usually is no penalty for these extra amounts. Check with your lender to make sure there is no penalty if you think you might want to make this type of additional principal prepayment.

Conversion Fees

Your agreement with the lender may include a clause that lets you convert the ARM to a fixed-rate mortgage at designated times. When you convert, the new rate is generally set using a formula given in your loan documents.

The interest rate or up-front fees may be somewhat higher for a convertible ARM. Also, a convertible ARM may require a fee at the time of conversion.

Graduated-payment or stepped-rate loans

Some fixed-rate loans start with one rate for 1 or 2 years and then change to another rate for the remaining term of the loan. While these are not ARMs, your payment will go up according to the terms of your contract. Talk with your lender or broker and read the information provided to you to make sure you understand when and by how much the payment will change.

Where to get Information

Disclosures from lenders

You should receive information in writing about each ARM program you are interested in before you have paid a nonrefundable fee. It is important that you read this information and ask the lender or broker about anything you don’t understand—index rates, margins, caps, and other ARM features such as negative amortization. After you have applied for a loan, you will get more information from the lender about your loan, including the APR, a payment schedule, and whether the loan has a prepayment penalty.

The APR is the cost of your credit as a yearly rate. It takes into account interest, points paid on the loan, any fees paid to the lender for making the loan, and any mortgage insurance premiums you may have to pay. You can compare APRs on similar ARMs (for example, compare APRs on a 5/1 and a 3/1 ARM) to determine  which loan will cost you less in the long term, but you should keep in mind that because the interest rate for an ARM can change, APRs on ARMs cannot be compared directly to APRs for fixed-rate mortgages.

Newspapers and the Internet

When buying a home or refinancing your existing mortgage, remember to shop around. Compare costs and terms, and negotiate for the best deal. Your local newspaper and the Internet are good places to start shopping for a loan. You can usually find information on interest rates and points for several lenders. Since rates and points can change daily, you’ll want to check information sources often when shopping for a home loan.


Any initial information you receive about mortgages probably will come from advertisements or mail solicitations from builders, real estate brokers, mortgage brokers, and lenders. Although this information can be helpful, keep in mind that these are marketing materials—the ads and mailings are designed to make the mortgage look as attractive as possible. These ads may play up low initial interest rates and monthly payments, without emphasizing that those rates and payments could increase substantially later. So, get all the facts.

Any ad for an ARM that shows an initial interest rate should also show how long the rate is in effect and the APR on the loan. If the APR is much higher than the initial rate, your payments may increase a lot after the introductory period, even if interest rates stay the same.

Choosing a mortgage may be the most important financial decision you will make. You are entitled to have all the information you need to make the right decision. Don’t hesitate to ask questions about ARM features when you talk to lenders, mortgage brokers, real estate agents, sellers, and your attorney, and keep asking until you get clear and complete answers.

Source: FTC:

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