Fixed vs Adjustable Rate Mortgages in 2026

For most of 2020-2022, almost no one took an adjustable-rate mortgage — fixed rates were so low there was no point. In 2026, with rates higher and a real possibility they fall over the next few years, ARMs are back on the table. Here is how they actually work, when the rate adjusts, and whether one makes sense for you.

What is an ARM, really?

An adjustable-rate mortgage (ARM) is a loan where the interest rate is fixed for an introductory period, then adjusts up or down on a schedule based on a public market rate. The introductory rate is usually lower than the rate on a comparable fixed loan, which is the whole appeal — you get a lower payment for the first several years.

The risk is that after the fixed period ends, the rate can rise, and so can your payment. ARMs have caps that limit how much the rate can move, but those caps can still allow meaningful payment shocks.

How the 5/1, 7/1, and 10/1 structures work

ARM names follow a [fixed years]/[adjustment interval] pattern:

• 5/1 ARM — rate is fixed for 5 years, then adjusts once per year for the remaining 25 years.
• 7/1 ARM — fixed for 7 years, then adjusts annually for 23 years.
• 10/1 ARM — fixed for 10 years, then adjusts annually for 20 years.

There are also 5/6, 7/6, and 10/6 ARMs, which adjust every 6 months instead of every 12 after the fixed period. The 6-month adjustment ARMs became more common after Fannie Mae updated its rules in 2023, but the 1-year adjustment interval is still the standard most borrowers encounter.

Index plus margin: how the new rate is set

When the fixed period ends, the new rate is calculated as:

newRate = index + margin

where:
  index  = a public market rate (usually SOFR or the 1-year Treasury)
  margin = a fixed percent set in your loan documents (typically 2.75%)

The index fluctuates with the market. The margin is fixed for the life of the loan and is the lender's markup. If the SOFR is at 4.5% and your margin is 2.75%, your new rate is 7.25% — subject to the caps below.

The caps that protect you

Every ARM has three caps that limit how much the rate can change:

• Initial adjustment cap — how much the rate can move at the first adjustment after the fixed period. Typically 2% or 5%.
• Periodic adjustment cap — how much the rate can move at each subsequent adjustment. Typically 2%.
• Lifetime cap — the maximum the rate can ever be above the initial rate. Typically 5% or 6%.

On a 5/1 ARM at 5.5% with a 2/2/5 cap structure: the first adjustment can move at most 2% (to 7.5%), each later adjustment at most 2%, and the rate can never exceed 10.5% (5.5% + 5%). Caps are your protection — read them before you sign.

Worked example: 5/1 ARM vs 30-year fixed

Suppose you are taking out a $400,000 loan. The 30-year fixed is at 6.5% ($2,528/month). The 5/1 ARM starts at 5.75% ($2,333/month). Here is how the comparison plays out under three scenarios for what the ARM rate does after year 5:

The ARM saves you $11,700 over the first 5 years ($195/month × 60 months). After year 5, the rate adjusts. If rates fall, you keep saving. If rates rise, your payment can jump significantly — up to the lifetime cap.

When an ARM wins

• You plan to move or sell within the fixed period. If you know you will sell in 5 years, a 5/1 ARM captures the lower rate and you are gone before the first adjustment.
• You plan to refinance within the fixed period. If you expect rates to fall and will refi before year 6, the ARM is a bridge to a lower fixed rate.
• The initial rate is meaningfully lower. If the spread between the ARM and the fixed is only 0.25%, the savings are not worth the risk. If it is 0.75% or more, the math gets interesting.
• You can absorb a payment increase. If the worst-case year-6 payment still fits your budget, the downside is manageable.

When a fixed rate wins

• You plan to stay long-term. The longer you keep the loan, the more likely the ARM adjusts upward at some point and erases the initial savings.
• You value predictability. A fixed payment for 30 years makes budgeting simple and removes interest-rate risk entirely.
• The rate spread is small. If the ARM is only 0.25% below the fixed, the savings are too thin to justify the risk of a future rate spike.
• You cannot absorb a payment increase. If the max-cap year-6 payment would be a stretch, the ARM is too risky.

The hybrid: ARM now, refi later

A common 2026 strategy is the "ARM bridge": take a 5/1 ARM at the lower rate, plan to refinance into a fixed before the first adjustment. This works if rates fall by year 5 — you captured the lower ARM rate for 5 years and refi into an even lower fixed. If rates rise instead, you are stuck refinancing into a higher fixed rate, or rolling the dice on the ARM adjusting up.

The hybrid is a bet on rates. If you are confident rates will fall within the fixed period, it is a reasonable play. If you are not sure, the fixed rate is the safer choice. Use the refinance calculator to model a future refinance and see if the math works.