Real Estate Glossary
What is Adjustable-Rate Mortgage (ARM)? Definition, Formula & Examples
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Definition
An adjustable-rate mortgage (ARM) is a home loan where the interest rate is fixed for an initial period (typically 3, 5, 7, or 10 years) and then adjusts periodically based on a benchmark index (usually SOFR or the 1-year Treasury) plus a fixed margin. ARMs often start with a lower rate than fixed mortgages, but carry the risk of rate increases after the fixed period ends.
Adjustable-Rate Mortgage (ARM) Example with Real Numbers
You get a 7/1 ARM at 6.25% on a $300,000 loan. For years 1–7, your monthly P&I is $1,848 — lower than the $1,996 payment on a 30-year fixed at 7%. After year 7, the rate adjusts annually. If the index rises and the new rate becomes 8.5%, your payment jumps to $2,254 — a $406/month increase. Most ARMs have annual caps (typically +2%) and lifetime caps (+5–6% over initial rate) to limit adjustment severity.
Why Adjustable-Rate Mortgage (ARM) Matters for Investors
ARMs can make sense for investors who plan to sell or refinance before the adjustable period begins, or who believe rates will fall. On a 5-year flip or BRRRR deal with a 5/1 ARM, the rate may never adjust before the property is sold or refinanced. However, rental property investors using ARMs must stress-test their cash flow at the maximum possible rate to ensure the deal still works if rates rise significantly.
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Frequently Asked Questions
What does 5/1 ARM mean?
The first number (5) is the fixed-rate period in years. The second number (1) is how often the rate adjusts after that — every 1 year. A 7/1 ARM is fixed for 7 years, then adjusts annually. A 5/6 ARM adjusts every 6 months after the initial period.
Are ARMs risky for rental properties?
They carry more risk than fixed mortgages because your mortgage payment can increase after the fixed period. On investment properties, a rate jump can flip positive cash flow to negative. Always model worst-case (lifetime cap) scenarios.
What index do ARMs use?
Most modern ARMs are tied to SOFR (Secured Overnight Financing Rate), which replaced LIBOR. The new rate = SOFR + your loan's margin (typically 2.5–3.5%). Some older loans still use the 1-year CMT (Constant Maturity Treasury).
Can I refinance out of an ARM before it adjusts?
Yes. Many investors use ARMs specifically for their lower initial rate with the intent to refinance or sell before the adjustment period. This strategy requires confidence in either the property's refinanceability or marketability at that point.
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