What Is an Adjustable-Rate Mortgage (ARM)? Pros, Cons & When It Makes Sense

An adjustable-rate mortgage (ARM) can save you thousands in the early years of homeownership — or cost you thousands if rates rise at the wrong time. Understanding exactly how ARMs work is essential before choosing between a fixed-rate and adjustable-rate loan.

How an ARM Works

An ARM has two phases. First comes the initial fixed-rate period — typically 5, 7, or 10 years — during which your rate doesn't move. Then comes the adjustment period, where your rate resets annually based on a benchmark index (usually SOFR) plus a margin set by the lender.

You'll see ARMs written as '5/1,' '7/1,' or '10/1.' The first number is the fixed period in years; the second is how often it adjusts after that. A 7/1 ARM stays fixed for 7 years, then adjusts once per year.

ARM Caps: Your Protection Against Rate Spikes

Every ARM comes with rate caps that limit how much your rate can change. There are three types:

• Initial cap: max increase at the first adjustment (often 2%)
• Periodic cap: max increase at each subsequent adjustment (often 2%)
• Lifetime cap: max total increase over the life of the loan (often 5–6%)

So on a 5/1 ARM at 6.5% with 2/2/5 caps: after year 5, your rate can jump to at most 8.5%. After year 6, at most 10.5%. And it can never exceed 11.5% total.

ARM vs Fixed-Rate: The Real Math

On a $400,000 loan, a 7/1 ARM at 6.0% vs a 30-year fixed at 7.0% saves about $280/month in the fixed period — over $23,000 in 7 years. But if rates rise and your ARM hits its periodic caps after year 7, your payment could jump $500–$700/month.

When an ARM Makes Sense

• You plan to sell or refinance before the fixed period ends
• You expect income to rise significantly before adjustment kicks in
• You're buying in a high-rate environment where fixed rates are unusually elevated
• The rate spread between ARM and fixed is 1% or more

When to Stick With a Fixed-Rate Mortgage

• You plan to stay in the home long-term (10+ years)
• Rates are already historically low
• Your budget has little room to absorb a payment increase
• You value predictability over potential savings