Fixed vs Adjustable Rate Mortgage: Which One Wins in 2026?

The short answer

On a $400,000 loan, a 6.50% fixed mortgage costs $2,528.27 a month, every month, for 30 years. A 5.50% adjustable-rate mortgage starts at $2,271.16 a month — $257.11 less — holds that rate for 5 years, and then adjusts to 7.50%, which pushes the payment to $2,733.10 a month. Over 10 years the fixed loan costs $303,392.65 and the ARM costs $300,255.53, so the ARM saves $3,137.12. The ARM wins, but only by about 1% of what you pay, and only if the adjusted rate stays below 7.72%. If you plan to move within a few years, the ARM is the better deal; if you plan to stay for decades, the fixed rate is the safer one.

The $257.11 question: what the ARM buys you

The ARM’s whole pitch is the first five years. At 5.50% instead of 6.50%, the monthly payment on $400,000 is $2,271.16 instead of $2,528.27, and $257.11 a month for 60 months is roughly $15,427 that stays in your pocket. That is real money: it covers moving costs, furniture, or a year of higher payments later. But notice what it does not do: after 5 years of ARM payments you still owe $369,842.41, because most of each early payment is interest. The ARM still pays the loan down faster than the fixed loan in those first years — at 5.50% you repay $30,157.59 of principal in 5 years, against $25,556.09 at 6.50%, because the lower rate means more of each payment goes to principal.

What happens at year 5: the $2,733.10 payment

The adjustment is where ARMs earn their reputation. The balance of $369,842.41 is re-amortized over the remaining 25 years at 7.50%, and the new payment is $2,733.10 a month — $204.83 more than the fixed payment, and $461.94 more than the ARM payment you were used to. Over the second five years the ARM costs about $12,290 more than the fixed loan, so it gives back most of its roughly $15,427 early saving. That is why the 10-year win is only $3,137.12: the cheap first half and the expensive second half nearly cancel out, and the ARM keeps only the difference. The interest tells the same story: over 10 years the fixed loan costs $242,497.16 in interest, against $239,521.41 for the ARM, but the fixed loan also repays $161.37 more principal, so it leaves you owing $161.37 less after 10 years.

The break-even: 7.72%

Every fixed-vs-adjustable decision comes down to one number: the adjusted rate at which the two loans cost exactly the same over your horizon. Here it is 7.72%, found by solving for the adjusted rate that makes the 10-year ARM total equal the fixed total of $303,392.65. If the ARM adjusts to anything below 7.72%, the ARM wins; above it, the fixed loan wins. That gives you a concrete way to decide: if you believe rates in five years will be at or below 7.72%, take the ARM; if you believe they will be higher, take the fixed rate. And the break-even moves with your horizon: over 5 years there is no adjustment at all, so the ARM wins outright; over 15 years the adjusted rate matters for twice as long, so the break-even is lower.

When the ARM wins big — and when it loses

The ARM’s best case is an adjusted rate that barely rises. If the ARM adjusts to 6.50% — no higher than the fixed rate — the new payment is $2,497.20 a month and the 10-year ARM total is $286,101.51, so the ARM saves $17,291.14. That is the outcome if rates stay flat or fall. The worst case is a sharp rise: if the ARM adjusts to 9.50%, the payment jumps to $3,231.30 a month and the 10-year ARM total is $330,147.41, so the ARM costs $26,754.76 more than the fixed loan. The range between those two outcomes is $44,045.90 — the ARM is a bet, and the fixed rate is the price of not betting.

The 7-year fixed period and the $300,000 version

Two variations show how the shape of the deal changes. With a 7-year fixed period instead of 5, the ARM stays cheap for two more years, the balance at adjustment is lower at $355,263.55, the new payment at 7.50% is $2,704.94 a month, and the 10-year ARM total is $288,154.89 — a bigger win than the 5-year version, because you keep more cheap years and fewer expensive ones. On a smaller $300,000 loan the same shape appears at three-quarter scale: the fixed payment is $1,896.20, the ARM starts at $1,703.37 and adjusts to $2,049.83, and the 10-year totals are $227,544.49 fixed against $225,191.65 ARM. The lesson is the same at any loan size: the longer the cheap period, the better the ARM looks.

What the numbers leave out

The calculator is exact for the numbers you enter, but it simplifies a real ARM in three ways that matter. First, real ARMs do not jump once to a single adjusted rate: after the fixed period they usually adjust every 6 or 12 months, following an index plus a margin, so the second-half payments move in steps rather than jumping to $2,733.10 all at once. Second, most ARMs have caps — typically 2% per adjustment and 5% over the life of the loan — which limit how bad the worst case can get; the 9.50% branch in this guide would be impossible under a 5% lifetime cap on a 5.50% start. Third, the model ignores closing costs, points, and the tax treatment of mortgage interest, and it assumes you stay for the full 10-year horizon. If you sell or refinance sooner, the ARM’s advantage grows, because you keep more cheap years and fewer expensive ones.

The verdict

Take the ARM if you will move or refinance before the adjustment, if you can afford the adjusted payment of $2,733.10 a month, or if you believe rates will stay below the 7.72% break-even: at an adjusted rate of 6.50% it saves $17,291.14 over 10 years, and with a 7-year fixed period it saves even more. Take the fixed rate if you will stay for decades, if the $2,733.10 adjusted payment would stretch your budget, or if you believe rates will rise past 7.72%: at 9.50% the fixed loan saves $26,754.76. And remember the edge case that settles the argument outright: if the fixed rate is 5.50%, the fixed payment is $2,271.16, exactly the ARM’s starting payment, so there is no reason to take the rate risk at all. Run your own numbers in the fixed vs adjustable rate mortgage calculator before you choose.