Adjustable-Rate Mortgage
An Adjustable-Rate Mortgage (ARM) is a residential mortgage loan on which the interest rate is fixed for an initial period — typically three, five, seven, or ten years — and then adjusts periodically based on a specified market index plus a fixed margin, resulting in monthly payment changes that can increase or decrease over the loan's remaining term.
Adjustable-rate mortgages are structured in contrast to fixed-rate mortgages, on which the interest rate and monthly payment remain constant for the full loan term. The ARM structure transfers some interest rate risk from the lender to the borrower: if rates rise, the borrower's payments increase after the initial fixed period; if rates fall, the borrower benefits from lower payments without needing to refinance.
ARM products in the U.S. market are described by their initial fixed period and adjustment frequency using a common shorthand. A 5/1 ARM has a fixed rate for the first five years and adjusts annually thereafter. A 7/6 ARM is fixed for seven years and adjusts every six months. The initial rate on an ARM is typically lower than the prevailing rate on a 30-year fixed-rate mortgage, reflecting the lender's reduced long-term rate risk, which is the primary financial incentive for borrowers to choose this structure.
After the initial fixed period expires, the ARM rate adjusts based on a reference index plus a contractual margin. The most common contemporary index for U.S. ARMs is the Secured Overnight Financing Rate (SOFR), which replaced LIBOR as the dominant ARM benchmark following LIBOR's discontinuation in 2023. The margin — typically 2.25% to 3.00% — is set at origination and remains constant for the life of the loan. Each adjustment date, the new rate equals the current index value plus the margin, subject to periodic and lifetime caps.
Caps are a critical consumer protection feature of U.S. ARM products. A typical ARM includes three types of caps: an initial adjustment cap (commonly 2% or 5%) limiting how much the rate can change on the first adjustment, a periodic adjustment cap (typically 2%) limiting changes on each subsequent adjustment, and a lifetime cap (typically 5% to 6%) limiting the total rate increase over the original note rate across the entire loan term. These caps protect borrowers from extreme payment shock in rapidly rising rate environments.
ARMs are particularly attractive when the initial fixed period aligns with a borrower's anticipated holding horizon. A buyer who plans to sell or refinance within five years has limited exposure to rate adjustments on a 5/1 ARM, allowing them to benefit from the lower initial rate without ever experiencing an adjustment. Borrowers who remain in their home past the fixed period must accept rate uncertainty or refinance before adjustment begins.
The percentage of U.S. mortgage originations accounted for by ARMs varies significantly with the interest rate environment. When fixed rates are low, the cost savings of choosing an ARM are modest and borrowers tend to favor fixed-rate certainty. When fixed rates rise sharply — as they did in 2022-2023 — ARM applications increase as borrowers seek to mitigate the cost of higher fixed rates through the lower initial ARM rate.