Adjustable Rate Mortgage (ARM)

What Is an Adjustable Rate Mortgage?

An adjustable rate mortgage, or ARM, is a loan with an interest rate that changes periodically based on market conditions. The rate is composed of two parts: an index, which is a benchmark rate like the Secured Overnight Financing Rate (SOFR), and a margin, which is a fixed percentage the lender adds on top. When the index rises, your rate rises. When it falls, your rate falls. ARMs contrast with fixed-rate mortgages where the rate never changes over the entire loan term.

ARM Structures Explained

ARMs are described by their adjustment schedule. A 5/1 ARM has a fixed rate for the first 5 years, then adjusts annually. A 7/1 ARM is fixed for 7 years with annual adjustments after. A 5/6 ARM is fixed for 5 years, then adjusts every 6 months. The initial fixed period almost always offers a lower rate than a comparable 30-year fixed mortgage, which is the primary attraction. The trade-off is uncertainty about future payments once the adjustable period begins.

Rate Caps and Payment Limits

ARMs include cap structures that limit how much the rate can change. A typical cap structure might be 2/2/5, meaning the rate cannot increase more than 2% at the first adjustment, 2% at any subsequent adjustment, and 5% over the life of the loan. If your initial rate is 6%, the lifetime cap means it can never exceed 11%. These caps provide some protection, but investors must model worst-case scenarios to ensure the property remains cash flow positive even at the maximum rate.

When ARMs Make Sense for Investors

ARMs are strategically valuable when you plan to sell or refinance before the fixed period ends. If you are executing a 3 to 5 year value-add strategy on a multifamily property, a 5/1 ARM gives you a lower rate during your entire hold period. If you believe rates will decline in coming years, an ARM lets you benefit from falling rates without refinancing. The key is matching the ARM's fixed period to your investment timeline. Never use an ARM on a long-term hold unless you are comfortable with payment variability.

ARM Risks and Mitigation

The primary risk is payment shock when the rate adjusts upward. If your rate jumps from 6% to 8% on a $300,000 loan, your monthly payment increases by roughly $400. On a thin-margin rental property, this can flip you from positive to negative cash flow overnight. Mitigate this risk by only using ARMs on properties with substantial cash flow cushion, maintaining reserves to cover potential payment increases, and having a refinance or sale plan well before the adjustment date.

Comparing ARMs to Fixed-Rate Options

Run the numbers both ways on every deal. Calculate your total interest cost and cash flow using the ARM rate for your planned hold period versus a 30-year fixed rate. If a 5/1 ARM saves you 0.75% on rate for a property you plan to hold for 4 years, that savings compounds across every monthly payment. On a $250,000 loan, that could mean $1,500 to $2,000 per year in improved cash flow. But if your plans change and you hold past the fixed period, model the worst case to ensure you can absorb adjustments without distress.