An adjustable-rate mortgage (ARM) is a home loan where the interest rate is fixed for an initial period, then adjusts periodically based on market conditions. Your payment can go down — or up — after the fixed period ends.
How ARMs actually work
- The fixed period. A “5/1 ARM” keeps its starting rate for 5 years, then adjusts once a year. Common fixed periods are 5, 7, or 10 years.
- Index plus margin. After the fixed period, your rate equals a published index plus the lender’s margin. The loan documents spell out exactly which index.
- Caps limit the damage. ARMs carry three caps: how much the rate can change at the first adjustment, how much it can change per later adjustment, and the lifetime maximum (ceiling). Read all three.
- The worst-case payment is knowable. Your lender can show you the highest your payment could go. Look at that number before anything else.
Why borrowers choose ARMs
- A lower starting rate than a comparable fixed-rate loan, which means a lower initial payment.
- A shorter time horizon. If you’ll sell or refinance before the fixed period ends, you may never face an adjustment.
- Rate environments. When fixed rates are elevated, as they have been through 2026, some buyers use ARMs to get a lower payment now while preserving the option to refinance later if rates fall.
The risks
If rates rise, your payment can rise substantially at each adjustment — up to the caps. Borrowers get hurt when they stretch to afford the starting payment and can’t absorb the adjusted one, or when their plan to sell or refinance falls apart.
Who it’s for
An ARM can make sense if the starting payment is comfortable, you understand the worst-case payment, and you have a realistic plan for the adjustment — whether that’s selling, refinancing, or simply affording the higher amount. If you’d lose sleep over a changing payment, a fixed-rate loan is worth the peace of mind. Talk through both options with your lender and a financial advisor before deciding.