Adjustable rate mortgages were once the majority product in residential lending and nearly destroyed the financial system when they were combined with lax underwriting in 2004-2007. Today they're a smaller share of the market, but they remain in use and remain capable of creating serious problems for borrowers who don't understand the adjustment mechanics.
How ARM Loans Work
An adjustable rate mortgage has a fixed-rate period followed by an adjustment period. A 5/1 ARM is fixed for 5 years and then adjusts annually. A 7/1 ARM is fixed for 7 years. The adjustment is calculated by adding a margin set in the loan documents to a published index. Common indexes include the Secured Overnight Financing Rate (SOFR), which replaced LIBOR, and the 1-year Treasury rate.
The margin is fixed for the life of the loan. The index changes based on market conditions. When the index rises, your rate rises. When the index falls, your rate falls, subject to floors built into many ARM structures.
The Caps Don't Protect You as Much as They Sound
ARM loans typically have three caps: the initial adjustment cap (how much the rate can change at the first adjustment), the periodic cap (how much it can change at each subsequent adjustment), and the lifetime cap (the maximum the rate can ever exceed the initial rate).
A common structure is 2/2/5: the rate can increase 2% at first adjustment, 2% at each subsequent adjustment, and no more than 5% over the life of the loan. On a loan starting at 6%, that's a maximum rate of 11%. The payment at 11% on a $500,000 mortgage is very different from the payment at 6%. Borrowers who qualified at 6% often cannot afford payments at 11%.
Rate caps sound protective. What they're actually doing is defining the worst case. If the worst case is an 11% rate, that's not protection. That's a risk boundary.
Index Risk and Opaque Rate Setting
Some older ARM products used indexes that were easier for lenders to influence or that moved in ways less correlated with market rates. LIBOR, which has now been retired, was shown to be subject to manipulation by major banks. SOFR, its replacement, is more robust but still tied to market conditions borrowers don't control.
When a borrower asks what their rate will be at the next adjustment, the honest answer is that it depends on where the index goes. There is no certain answer, and borrowers should be skeptical of any loan officer who implies otherwise.
Qualifying Rate vs. Payment Shock
The most dangerous aspect of ARM lending is the gap between the qualifying rate and the fully indexed rate. Lenders are supposed to qualify borrowers at the fully indexed rate under current rules, but in some loan categories and in some non-QM products, the qualifying rate is more favorable than the worst-case payment scenario.
Even when qualifying is done correctly, a borrower who barely qualifies at the start rate may find themselves unable to handle the payment if the rate adjusts upward by 2% at the first cap. Planning for higher payments is not optional in an ARM loan.
When ARMs Make Sense
An ARM can be a reasonable choice for a borrower who is confident they will sell the property before the first adjustment, who has strong income growth that will make future payment increases manageable, or who is refinancing into a fixed loan within the fixed period. The key is that the plan for handling the adjustment must be realistic, not just optimistic.
Coventry Enterprises LLC reviews ARM loan structures for borrowers before closing. Related: adjustable rate mortgage risks and toxic lending overview.