An adjustable-rate mortgage (ARM) combines an initial fixed-rate period with an interest rate that can change later. For some homebuyers, that structure can be attractive, especially when the initial ARM rate is competitive with available fixed-rate options.
However, an ARM also introduces uncertainty. Once the fixed period ends, your interest rate and principal and interest payment may increase or decrease according to the terms of the loan. Understanding exactly how those adjustments work is essential before choosing an ARM.
How Does an Adjustable-Rate Mortgage Work?
An ARM typically begins with an interest rate that remains fixed for a specified period. After that introductory period, the rate adjusts at scheduled intervals.
ARM names can help describe this structure. For example, a 5/1 ARM generally has a fixed rate for the first five years and then adjusts once per year. A 5/6 ARM generally stays fixed for five years and then adjusts every six months.
Other structures are available, so always verify the actual adjustment schedule in your loan documents rather than relying only on the ARM's name.
How Is an ARM Rate Calculated?
After the initial fixed period, an ARM rate is generally based on an index plus a margin, subject to the terms and rate caps of the mortgage.
- Index: A benchmark interest rate that changes with market conditions.
- Margin: A set number of percentage points established in the loan agreement.
When the index changes, the interest rate on the ARM can change at the next scheduled adjustment. The margin generally remains the same after closing.
For example, Fannie Mae's current conventional ARM plans use the 30-day average Secured Overnight Financing Rate (SOFR) as their index. Other ARM products may use different indexes, so borrowers should confirm the index specified for the mortgage they are considering.
What Are ARM Rate Caps?
Rate caps limit how much an ARM interest rate can change. These protections are important because they help define the maximum potential rate movement permitted under the loan terms.
- Initial adjustment cap: Limits how much the rate can change at the first adjustment after the fixed period.
- Subsequent adjustment cap: Limits how much the rate can change during later adjustment periods.
- Lifetime adjustment cap: Limits how much the rate can change over the life of the mortgage.
The Consumer Financial Protection Bureau notes that cap structures vary among ARMs. Do not assume one ARM has the same limits as another. Review your Loan Estimate and loan disclosures to understand the maximum rate and payment you could face.
Why Do Some Homebuyers Choose an ARM?
Some ARMs begin with a lower interest rate than comparable fixed-rate mortgages, although that is not guaranteed. When the initial ARM pricing is favorable, borrowers may benefit from a lower principal and interest payment during the fixed period.
An ARM may be worth considering if you expect to own the property for a limited period, understand the potential payment changes, and are financially prepared if the rate increases.
However, choosing an ARM solely because you expect to sell or refinance before the first adjustment can create risk. Your plans, home value, financial situation, and future mortgage rates could change.
What Are the Risks of an Adjustable-Rate Mortgage?
The primary risk is that your interest rate and payment can increase after the fixed period ends.
Before selecting an ARM, consider whether you could comfortably handle a higher payment if rates move upward. The CFPB recommends understanding how high your interest rate and monthly payment could go, how frequently adjustments occur, and how soon the first increase could happen.
An ARM can also make budgeting less predictable. Even if the initial payment fits comfortably today, future adjustments could affect your monthly housing expenses.
ARM vs Fixed-Rate Mortgage: Which Is Better?
Neither structure is automatically better for every borrower.
A fixed-rate mortgage provides greater predictability because the mortgage interest rate does not change over the life of the loan. An ARM provides an initial fixed period followed by the possibility of future rate changes.
When comparing the two, look beyond the starting rate. Compare the initial payment, adjustment schedule, index, margin, rate caps, maximum possible payment, closing costs, and how long you realistically expect to keep the mortgage.
Florida homebuyers should also consider the complete housing budget, including property taxes, homeowners insurance, flood insurance when applicable, and association fees. A mortgage payment that could increase later should leave enough room for other housing costs that may also change.
Questions to Ask Before Choosing an ARM
Before committing to an adjustable-rate mortgage, make sure you can answer these questions:
- How long will my initial interest rate remain fixed?
- When can my rate adjust for the first time?
- How frequently can it adjust afterward?
- Which index does the loan use?
- What is the margin?
- What are the initial, subsequent, and lifetime rate caps?
- Is there a minimum rate or floor?
- What is the highest interest rate allowed under the loan terms?
- What could my principal and interest payment become at that rate?
Your Loan Estimate provides important information about whether the rate is adjustable and how the loan can change. Review these details carefully and ask questions about anything you do not understand before closing.
The Bottom Line
An adjustable-rate mortgage can be a useful financing option when its structure fits your budget, timeline, and tolerance for future payment changes. The key is understanding both phases of the loan, not simply focusing on the introductory rate.
Before choosing an ARM, review the fixed period, adjustment frequency, index, margin, rate caps, and maximum potential payment. Also consider what would happen if you kept the home longer than planned and refinancing was not attractive or available when the fixed period ended.
Loan Wolf Lending can help Florida homebuyers compare adjustable-rate and fixed-rate mortgage options based on their financing goals. Call 754-755-3075 to discuss available mortgage options.