A 5/1 adjustable-rate mortgage locks your interest rate for the first five years, then adjusts once a year for the remaining term of the loan. The opening rate is typically a quarter to a full percentage point below a comparable 30-year fixed, which means a lower monthly payment during that five-year window. After year five, the rate and payment can move up or down with the market, within limits spelled out in your loan contract.
What the Numbers 5 and 1 Mean
The first number is the length of the fixed period in years. For the first five years, your rate stays exactly where it was set at closing, and your payment doesn’t change regardless of what happens in the broader economy.
The second number is how often the rate resets after that: once per year. Most 5/1 ARMs carry a total term of 30 years, so after the five-year lock ends you face up to 25 annual adjustments. That cycle continues until you pay off the balance, sell the home, or reach the end of the term. If you move or refinance before year six, you keep the benefit of the lower introductory rate without ever experiencing an adjustment.
How Your Rate Is Set Each Year After the Fixed Period
Once your rate starts adjusting, two numbers combine to set it: an index and a margin.
The index is a market benchmark. For new ARMs, the standard index is the Secured Overnight Financing Rate, known as SOFR, which replaced the older LIBOR benchmark after regulators phased it out.1Federal Register. Adjustable Rate Mortgages – Transitioning From LIBOR to Alternate Indices The margin is a fixed percentage your lender adds on top of the index. It’s set at closing and never changes, typically falling between 2 and 3.5 percentage points depending on the lender and your credit profile.
Adding the current index value to your margin gives you the “fully indexed rate,” which is what you pay for the next 12 months. If SOFR sits at 4 percent and your margin is 2.75 percent, your fully indexed rate for that adjustment period is 6.75 percent. The next year, only the index moves. A lower SOFR means a lower rate; a higher SOFR means a higher one.
Caps That Limit How Much Your Rate Can Change
Your contract includes rate caps that protect you from unlimited swings. They come in three layers:
- Initial adjustment cap. Limits how much your rate can change at the first reset after the five-year fixed period, commonly set at either 2 or 5 percentage points.2Consumer Financial Protection Bureau. What Are Rate Caps With an Adjustable-Rate Mortgage (ARM), and How Do They Work
- Periodic adjustment cap. Limits the change at each annual adjustment after the first, most commonly 1 or 2 percentage points.2Consumer Financial Protection Bureau. What Are Rate Caps With an Adjustable-Rate Mortgage (ARM), and How Do They Work
- Lifetime cap. Sets an absolute ceiling your rate can never exceed over the life of the loan, most commonly 5 percentage points above your initial rate.2Consumer Financial Protection Bureau. What Are Rate Caps With an Adjustable-Rate Mortgage (ARM), and How Do They Work
You’ll often see the three caps written in shorthand like 2/2/5. That means the rate can rise up to 2 points at the first adjustment, up to 2 points at each later adjustment, and no more than 5 points above the starting rate over the life of the loan. If your starting rate is 5 percent under a 2/2/5 structure, the highest your rate can ever reach is 10 percent.
There’s also a floor. Caps work in both directions, but even if the market index drops sharply, your rate can’t fall below the margin written into your loan.3Fannie Mae. Adjustable-Rate Mortgages (ARMs) A 2.75 percent margin means 2.75 percent is the lowest your interest rate can go, no matter how far the index falls.
How Your Monthly Payment Gets Recalculated
Each time your rate adjusts, the lender re-amortizes the loan. The servicer takes your current remaining balance, not the original loan amount, applies the new interest rate, and spreads the payments over the time left on the loan.4Fannie Mae. F-1-01 Servicing ARM Loans If you’re entering year six of a 30-year mortgage, the new payment is calculated over the remaining 24 years.
The recalculated payment covers interest at the new rate plus enough principal to pay the loan off by the original maturity date. A standard 5/1 ARM doesn’t allow negative amortization, so your balance won’t grow. Your payment always covers the full interest charge and some principal. The recalculation happens every year during the adjustable period, so the amount you owe each month can change annually until the loan is paid off.
Notice Before Your First Adjustment
You won’t be caught off guard by the first reset. Before your rate adjusts for the first time, your loan servicer must send a written notice at least 210 days, but no more than 240 days, before the first payment at the new rate is due.5Consumer Financial Protection Bureau. 1026.20 Disclosure Requirements Regarding Post-Consummation Events That’s roughly seven to eight months of lead time to plan for the new payment, shop for a refinance, or decide to sell. For a 5/1 ARM, the notice typically arrives about halfway through your fourth year.
Paying Off Early or Refinancing
Federal rules that took effect in 2014 effectively bar prepayment penalties on adjustable-rate mortgages. A lender can only charge a prepayment penalty if the loan’s interest rate cannot increase after closing, which limits the exception to fixed-rate qualified mortgages.6eCFR. 12 CFR 1026.43 – Minimum Standards for Transactions Secured by a Dwelling Because a 5/1 ARM’s rate adjusts after year five, it doesn’t fit that exception.
You can pay the loan off early, make extra principal payments, sell the home, or refinance into a different mortgage at any time without a penalty. For borrowers who choose an ARM specifically because they expect to move or refinance before the adjustable period starts, that’s a meaningful protection.
When a 5/1 ARM Fits, and When It Doesn’t
The structure tends to work in a few specific situations:
- You expect to sell before year six, so you collect the savings from the lower introductory rate and are gone before the adjustable period begins.
- You plan to refinance within five years, whether because you expect rates to drop or because you expect your credit and income to improve enough to qualify for better terms.
- Your income is likely to rise meaningfully, making a potentially higher payment in year six easier to absorb than it would be today.
The risk is the mirror image. If you still own the home when the adjustable period starts and market rates have climbed, your payments can increase substantially, up to the cap limits in your contract. On a loan with a 2/2/5 cap structure and a 5 percent starting rate, your rate could reach 7 percent at the first adjustment and eventually 10 percent. Running a worst-case payment through your budget before you sign tells you whether that outcome is survivable.