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What Is an Adjustable-Rate Mortgage (ARM)?
Key takeaways
- An adjustable-rate mortgage offers a fixed interest rate for an initial period, then adjusts periodically based on your loan terms and market conditions
- ARMs typically start with lower rates than fixed mortgages, making them attractive for short-term homeowners or those planning to refinance before adjustments begin
- Rate adjustments are calculated using an index rate plus a fixed margin. ARMs often have caps that limit the potential increases at each adjustment period and over the life of the loan
An adjustable-rate mortgage (ARM) is a type of home loan where the interest rate can change periodically.
During an initial period, typically 3, 5, 7, or 10 years, your rate is locked in. Afterward, it can change at regular intervals and your monthly payment could go up or down depending on market conditions.
ARMs typically start with a lower initial interest rate than fixed-rate mortgages, making them appealing for buyers who find the rates for fixed-rate mortgages to be too high, who plan to refinance before rate adjustments begin, or who plan to own a home for a limited time.
How are ARMs structured?
You’ll often see ARMs written in a format like 5/1, 7/1, or 10/6. The first number gives the length, in years, of the introductory fixed-rate period. The second number indicates how frequently the rate can be adjusted once the fixed period ends.
Common ARM examples
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5/1 ARM: Fixed for the first 5 years, adjusts once a year thereafter
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7/1 ARM: Fixed for 7 years, then adjusts annually
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10/6 ARM: Fixed for 10 years, then adjusts every 6 months
How do adjustable-rate changes work?
When the fixed-rate period ends, your lender recalculates your interest rate based on three components: ARM index, margin, and adjustment caps.
1. The index rate
The ARM index rate reflects overall market conditions. Lenders typically base their index on Treasury rates or the Secured Overnight Financing Rate (SOFR). These rates tend to reflect inflationary pressures in the economy, so adjustments to an ARM will tend to rise and fall with inflation.
2. The margin
The margin is a fixed percentage that lenders add to the index to determine your new rate. It stays the same throughout your loan, even when the index changes. Your credit score and credit history could affect the margin. Lenders might set a lower margin for loan applicants with a good credit history.
A rate change example
Let's say that your 5/1 ARM interest rate was 5.5% during the introductory period and it's time for the initial adjustment. Your lender's index is now at 4%, and your margin is 2%. If your cap allows it, your new interest rate would be 6% (4% + 2%).
When the next adjustment comes a year later, the lender's index is at 5%. Your new rate, if the cap allows it, would be 7% (5% + 2%).
What are the pros of adjustable-rate mortgages?
ARMs can make homeownership more affordable, especially in the short term.
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Lower initial interest rates. The introductory rate is usually lower than that of a fixed-rate loan, resulting in smaller monthly payments early on
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Ideal for short-term homeowners. If you plan to move, sell, or refinance within a few years—before the rate adjusts—you might save thousands compared to what you might spend with a fixed-rate mortgage
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Higher purchasing power. Lower initial payments may help you qualify for a larger loan amount
What are the cons of adjustable-rate mortgages
ARMs also carry some potential challenges to keep in mind.
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Rate uncertainty. After the fixed period ends, your rate could rise with market rates, increasing your monthly payment
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Budgeting challenges. It can be harder to predict long-term housing costs due to payment changes with an ARM
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Potential for payment shock. Sharp rate increases can cause noticeable jumps in your payment after the first adjustment
Who should consider an ARM?
An ARM might be a smart option for certain borrowers. You may want to consider an ARM if you:
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Expect to move within 5-10 years. If you sell the house before the rate adjusts, you could benefit from the lower initial rate without long-term risk
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You plan to refinance later. Many homeowners refinance into a fixed-rate mortgage before the adjustable period begins
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You want the lowest starting rate. ARMs offer access to some of the most competitive introductory rates
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You have strong income stability. If your finances can comfortably handle future payment increases, an ARM can help you save upfront. In addition, your credit score and ARM rates tend to go hand in hand: a higher credit score could result in a lower initial interest rate and lower margin
Who should choose a fixed-rate mortgage?
Fixed-rate mortgages may be particularly well-suited for borrowers who:
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Value consistent, predictable payments.
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Plan to stay in their home long term.
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Prefer a straightforward loan without adjustment periods.
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Want to avoid the risk of future rate increases.
This loan type is common among first-time homebuyers and families seeking long-term financial stability, though individual circumstances vary widely.
On the other hand, borrowers who value stability and predictable payments may prefer fixed-rate mortgages.
Adjustable-rate mortgage (ARM) |
Fixed-rate mortgage |
|
|---|---|---|
Initial rate |
Lower
|
Higher
|
Long-term rate stability |
Variable
|
Stable
|
Payment changes |
Yes
|
No
|
Best for |
Short-term buyers
|
Long-term homeowners
|
Are adjustable-rate mortgages risky?
ARMs aren’t inherently risky, but they do require awareness and planning. For one thing, you'll have to determine how much your payment could increase, given the rates and caps, and whether your budget could handle it.
When borrowers accurately evaluate the index, margin, rate caps, and adjustment schedule, ARMs can be a strategic way to save money during the early years of homeownership.
FAQs
The adjustment frequency depends on your loan structure. After the initial fixed period ends, common ARMs adjust annually or every six months.
The second number in the ARM designation indicates how often adjustments occur—for example, a 5/1 ARM adjusts once a year after the first 5 years.
Yes, many homeowners choose to refinance their ARM into a fixed-rate mortgage before the adjustable period begins. This strategy allows you to benefit from the lower initial ARM rate during the fixed period, then lock in predictable payments by refinancing before rate adjustments start. Refinancing is a common way to avoid payment uncertainty.
ARMs often include rate caps to protect borrowers from dramatic payment increases.
There are three common types: an initial adjustment cap limiting the first rate change, a periodic cap limiting subsequent adjustments, and a lifetime cap restricting the maximum rate increase over the entire loan term.
These caps can provide safeguards against rate volatility.
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