What Is an Adjustable-Rate Mortgage (ARM)?
In plain English
An adjustable-rate mortgage features an interest rate that changes periodically after an initial fixed period. A 5/1 ARM, for example, holds a fixed rate for five years, then adjusts annually. The new rate is based on a market index plus a lender margin. ARMs typically start lower than fixed-rate loans but introduce uncertainty about future payments.
How Are ARM Interest Rates Calculated After the Initial Period?
After the fixed period ends, the rate resets based on an index — commonly the Secured Overnight Financing Rate (SOFR) — plus a set margin. Rate caps limit how much the rate can rise at each adjustment and over the loan's lifetime. Common caps are 2/2/5, meaning no more than 2% increase at first adjustment, 2% per subsequent adjustment, and 5% total over the loan.
Who Should Consider an Adjustable-Rate Mortgage?
ARMs make sense for borrowers who expect to sell or refinance before the fixed period ends. They're also suitable for buyers confident rates will fall, or those who need a lower starting payment to qualify. Military families and people with predictable relocation timelines often favor ARMs. The key risk is holding the loan into the adjustable phase if rates have risen.
What Are the Risks of an Adjustable-Rate Mortgage?
Payment shock is the primary risk — your monthly payment can jump significantly when the rate adjusts. If your financial situation changes or you can't refinance before the adjustment, you could struggle. The 2008 housing crisis was partly driven by borrowers who couldn't afford their payments after ARM resets. Many experts recommend stress-testing a budget at the maximum capped rate before choosing an ARM.
Frequently asked questions
What does 5/1 ARM mean?
A 5/1 ARM has a fixed rate for the first five years, then adjusts once per year thereafter. The first number is the fixed period in years; the second is how often it adjusts after that.
Can an ARM rate go down as well as up?
Yes. If the underlying index falls, your ARM rate and payment can decrease. Caps apply in both directions on some loans. However, most borrowers focus on upside risk since rates can rise substantially over a 30-year term.
Keep exploring
Related terms
Fixed-Rate Mortgage
A fixed-rate mortgage locks in your interest rate for the entire loan term, so your principal and interest payment never changes. It offers predictability and protection against rising rates.
Mortgage
A mortgage is a loan used to purchase real estate, where the property itself serves as collateral. It's typically repaid over 15 or 30 years through monthly payments of principal and interest.
Refinancing
Refinancing replaces your existing mortgage with a new one, typically to get a lower interest rate or change loan terms. It can reduce monthly payments or help you pay off your home faster.
Down Payment
A down payment is the upfront cash you pay toward a home purchase, with the mortgage covering the rest. The larger your down payment, the less you borrow and the lower your monthly payments.
Rent vs. Buy
The rent vs. buy decision compares the true costs of renting a home to owning one. It depends on home prices, rent levels, your time horizon, and opportunity costs — not just monthly payment comparisons.