Mortgages: Fixed-Rate Versus Adjustable-Rate

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Fixed-rate mortgage and adjustable-rate mortgages (ARMs) are the two primary mortgage types. While the marketplace offers numerous varieties within these two categories, the first step when shopping for a mortgage is determining which of the two main loan types best suits your needs.

Fixed-Rate Mortgages

fixed-rate mortgage charges a set rate of interest that does not change throughout the life of the loan. Although the amount of principal and interest paid each month varies from payment to payment, the total payment remains the same, which makes budgeting easy for homeowners.

The partial amortization schedule below demonstrates the way in which the amounts put toward principal and interest alter over the life of the mortgage. In this example, the mortgage term is 30 years, the principal is $100,000 and the interest rate is 6%.

Payment Principal Interest Principal Balance
1. $599.55 $99.55 $500.00 $99900.45
2. $599.55 $100.05 $499.50 $99800.40
3. $599.55 $100.55 $499.00 $99699.85

As you can see, the payments made during the initial years of a mortgage consist primarily of interest payments.

The main advantage of a fixed-rate loan is that the borrower is protected from sudden and potentially significant increases in monthly mortgage payments if interest rates rise. Fixed-rate mortgages are easy to understand and vary little from lender to lender. The downside to fixed-rate mortgages is that when interest rates are high, qualifying for a loan is more difficult because the payments are less affordable.

Although the rate of interest is fixed, the total amount of interest you'll pay depends on the mortgage term. Traditional lending institutions offer fixed-rate mortgages in a variety of terms, the most common of which are 30, 20 and 15 years.

The 30-year mortgage is the most popular choice because it offers the lowest monthly payment; however, the trade-off for that low payment is a significantly higher overall cost because the extra decade, or more, in the term is devoted primarily to paying interest. The monthly payments for shorter-term mortgages are higher so that the principal is repaid in a shorter time frame. Also, shorter-term mortgages offer a lower interest rate, which allows for a larger amount of principal repaid with each mortgage payment. So shorter-term mortgages cost significantly less overall.

Adjustable-Rate Mortgages

The interest rate for an adjustable-rate mortgage is a variable one. The initial interest rate on an ARM is set below the market rate on a comparable fixed-rate loan, and then the rate rises as time goes on. If the ARM is held long enough, the interest rate will surpass the going rate for fixed-rate loans.

ARMs have a fixed period of time during which the initial interest rate remains constant, after which the interest rate adjusts at a pre-arranged frequency. The fixed-rate period can vary significantly – anywhere from one month to 10 years; shorter adjustment periods generally carry lower initial interest rates. After the initial term, the loan resets, meaning there is a new interest rate based on current market rates. This is then the rate until the next reset, which may be the following year.

ARM Terminology

ARMS are significantly more complicated than fixed-rate loans, so exploring the pros and cons requires an understanding of some basic terminology. Here are some concepts borrowers need to know before selecting an ARM.

  • Adjustment Frequency - This refers to the amount of time between interest-rate adjustments (e.g. monthly, yearly, etc.).
  • Adjustment Indexes - Interest-rate adjustments are tied to a benchmark. Sometimes this is the interest rate on a type of asset, such as certificates of deposit or Treasury bills. It could also be a specific index, such as the Cost of Funds Index or  the London Interbank Offered Rate (LIBOR). For details, see Adjustable-Rate Mortgage Indexes: Know Your Benchmark.)
  • Margin - When you sign your loan, you agree to pay a rate that is a certain percentage higher than the adjustment index. For example, your adjustable rate may be the rate of the one-year T-bill plus 2%. That extra 2% is called the margin.
  • Caps - This refers to the limit on the amount the interest rate can increase each adjustment period. Some ARMs also offer caps on the total monthly payment. These loans, also known as negative amortization loans, keep payments low; however, these payments may cover only a portion of the interest due. Unpaid interest becomes part of the principal. After years of paying the mortgage, your principal owed may be greater than the amount you initially borrowed.
  • Ceiling - This is the highest that the adjustable interest rate is permitted to become during the life of the loan.

The biggest advantage of an ARM is that it is considerably cheaper than a fixed-rate mortgage, at least for the first three, five or seven years. ARMs are also attractive because their low initial payments often enable the borrower to qualify for a larger loan and, in a falling interest rate environment, allow the borrower to enjoy lower interest rates (and lower payments) without the need to refinance the mortgage. A borrower who chooses an ARM  may save several hundred dollars a month for up to seven years, after which his costs may or may not rise. His new rate may be lower depending on what the market rates are like at the time of the rate reset.

The ARM, however, can pose some significant downsides. With an ARM, your monthly payment may change frequently over the life of the loan. And if you take on a large loan, you could be in trouble when interest rates rise: Some ARMs are structured so that interest rates can nearly double in just a few years. (For details, see Adjustable Rate Mortgage: What Happens When Interest Rates Go Up). In fact, adjustable-rate mortgages have been out of favour with many financial planners ever since the subprime mortgage meltdown of 2008, which ushered in an era of foreclosures and short sales. Back then, borrowers faced sticker shock when their ARMs adjusted, and their payments skyrocketed.

Which Loan Is Right for You?

When choosing a mortgage, you need to consider a wide range of personal factors and balance them with the economic realities of an ever-changing marketplace. Individuals' personal finances often experience periods of advance and decline, interest rates rise and fall, and the strength of the economy waxes and wanes. To put your loan selection into the context of these factors, consider the following questions:

  • How large of a mortgage payment can you afford today?
  • Could you still afford an ARM if interest rates rise?
  • How long do you intend to live on the property?
  • What direction are interest rates heading and do you anticipate that trend to continue?

A borrower considering an ARM should run the numbers to determine the worst-case scenario. If he can still afford it if the mortgage resets to the maximum cap in the future, an ARM will save him money every month. Ideally, the borrower should use the savings compared to a fixed rate mortgage to make extra principal payments each month so that the total loan is smaller when the reset occurs, further lowering costs.

If interest rates are high and expected to fall, an ARM will ensure that you get to take advantage of the drop, since you're not locked in to a particular rate. If interest rates are climbing or a steady, predictable payment is important to you, a fixed-rate mortgage may be the way to go.

Candidates for ARMs

The Short-Term Homeowner: An ARM may be an excellent choice if low payments in the near term are your primary requirement or if you don't plan to live in the property long enough for the rates to rise. As mentioned earlier, ARMs' fixed-rate periods vary, typically from one year to five years to seven years, which is why an ARM might not make sense for people who plan to keep their home for more than that. However, if you know you are going to move within a short period, or you don’t plan to hold on to the house for decades to come, then an adjustable-rate mortgage is going to make a lot of sense. Let’s say you take out a seven-year ARM with an interest rate of 3.5%. A 30-year fixed-rate mortgage, in comparison, is going to give you an interest rate of 4.25%. If you aim to move before the five-year ARM resets you are going to save a lot of money on interest, but if you ultimately decide to stay in the house longer, and rates are higher when your loan adjusts, then the mortgage is going to cost more. If you are purchasing a home with an eye toward upgrading to a bigger home once you start a family, or you think you’ll be relocating for work, then an ARM may be right for you.

The Bump-Up-in-Income Earner: For people who have a stable income but don’t expect their income to increase dramatically, a fixed-rate mortgage makes more sense. However, if you expect to see an increase in your income, going with an ARM could save you from paying a lot of interest over the long-haul. Let’s say you are looking for your first home and you just graduated from medical school, law school or earned an MBA. The chances are high that you are going to earn more in the coming years and will be able to afford the increased payments once your loan adjusts. In that case, an ARM will work for you. Or, you expect to start receiving money from a trust at a certain age; you could get an ARM that  resets in the same year. 

The Pay-it-Off Type: Taking out an adjustable-rate mortgage is very attractive to mortgage borrowers who have or will have the cash to pay off the loan before the new interest rate kicks in. While that doesn’t include the vast majority of Americans, there are situations where it may be possible to pull it off. Take a borrower who is buying one house and selling another one at the same time. That person may be forced to purchase the new home while the old one is in contract and, as a result will take out a one or two-year ARM. Once the borrower has the proceeds from the sale, he  can turn around to pay off the ARM with the proceeds from the home sale.

Another scenario in which an ARM would make sense is if you can afford to accelerate the payments each month by enough to pay it off before it resets. Employing this strategy can be risky because life happens and while you may be able to afford to make accelerated payments now, if you get sick, lose your job or the boiler goes, that may no longer be an option.

The Bottom Line

Regardless of the loan that you select, choosing carefully will help you avoid costly mistakes. One thing's for sure:  Don't go with the ARM because the lower monthly payment is the only way to afford that dream house. You may get a similar rate at the time of reset, but it is a serious gamble. It's more prudent to search for a place with a smaller price tag instead.

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