What do the numbers in '5/1 ARM' and '7/1 ARM' mean?

The first number is the teaser period in years — 5, 7, or 10. Your rate is fixed for that long. The second number is the adjustment frequency after the teaser — a '1' means the rate can reset every one year for the remainder of the term. Newer ARMs tied to SOFR instead of LIBOR sometimes reset every 6 months and are labeled 5/6m or 7/6m. The math is the same either way.

What does a 2/1/5 cap structure mean?

The three numbers are the first adjustment cap, periodic cap, and lifetime cap. 2/1/5 means: at the first reset your rate can jump at most 2%, every subsequent annual reset can change at most 1% up or down, and the rate can never exceed your starting rate + 5% over the life of the loan. The typical ARM today has 2/2/5 or 5/2/5 caps. Read your loan documents — these numbers are the only things that limit your downside.

When does an ARM actually save money vs. a fixed rate?

When you're certain to sell or refinance before the teaser period ends AND the teaser rate is meaningfully lower than the fixed rate. Historically the ARM-to-fixed spread was 0.5%–1%. Recently the spread has been smaller (sometimes ARMs are barely cheaper than 30-year fixed), which makes them less compelling. If you're planning to live in the house 10+ years, the fixed is usually the safer call — you trade certainty for a small monthly premium.

What happens if I can't refinance out before the reset?

Your payment jumps at the first adjustment, subject to the cap. On a $450,000 ARM at 5.75% with a 2% first-adjustment cap, your worst-case rate becomes 7.75%, and the payment jumps roughly $550–$650/month. You keep that higher payment unless rates drop enough to trigger another favorable reset. People who bought with ARMs assuming they could refi before reset got badly squeezed in 2022–2024 when rates spiked and refinancing didn't save money.

Are ARMs risky in general?

More than a fixed — yes, categorically. Fixed rates are a transferred-risk product: the lender takes the interest rate risk for you in exchange for a slightly higher initial rate. ARMs are the opposite: you take the interest rate risk and get compensated with a lower teaser. For a disciplined borrower with a short time horizon and an emergency fund that can absorb payment jumps, ARMs can make sense. For anyone stretching to qualify or planning to stay put for 10+ years, fixed is almost always the right choice.

ARM vs. Fixed Rate Mortgage Calculator | 5/1, 7/1 vs 30-Year Fixed

What an adjustable-rate mortgage actually costs

An ARM looks cheap on the surface. The monthly payment during the teaser period is often $200–$500 less than the equivalent 30-year fixed. That spread is real, but it's the price of shifting the interest rate risk from the bank to you. When the teaser period ends, your rate resets to whatever the market decides — and unlike a fixed mortgage, you can't lock today's rate for the life of the loan.

This calculator shows both sides: the savings during the teaser period AND the worst-case payment if rates reset to the cap. Enter your loan amount, teaser rate, fixed-rate alternative, and the specific cap structure in your loan documents. The output tells you exactly what you're gaining and what you're risking.

How ARMs work: the teaser, the reset, the caps

A hybrid ARM has two phases. Phase 1 is the teaser — a 5, 7, or 10 year period where your rate is fixed. Phase 2 is the adjustable period, where your rate resets periodically (usually annually) based on an index plus a margin.

The index is typically SOFR (the Secured Overnight Financing Rate, which replaced LIBOR in 2023). The margin is a fixed spread the lender adds — usually 2.25% to 2.75%. So if SOFR is 4% and your margin is 2.5%, your fully indexed rate would be 6.5%. Your contract rate is the lesser of (fully indexed) and (rate + cap).

The caps are your only protection. A typical 2/2/5 structure:

First adjustment cap (2%): at the first reset, your rate can rise at most 2% above the teaser. 5.75% teaser + 2% = 7.75% worst case at year 6.
Periodic cap (2%): every annual adjustment after that can change the rate at most 2% up or down.
Lifetime cap (5%): the rate can never exceed the teaser + 5%. 5.75% + 5% = 10.75% is the absolute worst case for this ARM.

Different lenders use different cap structures. 2/1/5 is common. 5/2/5 exists (a huge first-adjustment cap). Read your specific loan documents.

The case for an ARM

You're definitely moving before the reset.If you're buying a starter home you plan to sell in 4 years, a 5/1 ARM captures a lower rate during your entire occupancy. The teaser savings of $500/month for 60 months is $30,000 of real money — enough to meaningfully offset the next home's down payment.

Rates are expected to fall. If you believe the Fed is at peak rates and will cut over the next 3–5 years, an ARM lets you capture the cuts automatically at each reset, without the cost of refinancing. Fixed-rate borrowers have to pay closing costs to capture lower rates. See our refinance savings calculator.

You have big emergency savings.If you can comfortably absorb a payment jump of $500–$800/month at the worst case, the ARM is a bet you can afford to lose. If a payment jump would force you to sell, you can't afford the bet.

The teaser spread is large.Historically ARMs offered 0.75–1.25% savings vs. fixed. When the spread is 0.25% or less (as in much of 2024), the ARM risk-adjusted value is much weaker — it's like accepting interest rate risk for a tiny tip.

The case against an ARM

You're planning to stay 10+ years. The fixed rate is worth paying for. Certainty over three decades beats the marginal savings of the teaser.

You stretched to qualify.If you're at the top of your debt-to-income ratio on the teaser payment, you cannot afford the post-reset payment. Lenders are supposed to qualify you on the fully indexed rate for this reason, but they don't always — especially on jumbo or non-QM ARMs. See our DTI calculator to run the worst-case payment against your income.

You're buying near a market top.If values correct downward during the teaser period, you may owe more than the home is worth when the reset hits, meaning you can't refinance or sell without a loss. Underwater borrowers are the group most harmed by ARM resets.

The history: ARMs and the 2008 crisis

ARMs got a bad reputation in 2008 because millions of subprime borrowers had Option ARMs and 2/28 hybrid ARMs with teasers as short as two years. When those resets hit — often doubling the monthly payment — borrowers who couldn't refinance because their homes had dropped in value defaulted en masse.

Post-2010 Dodd-Frank regulations fixed the worst abuses. Teaser periods under 5 years are effectively extinct. Lenders are required to qualify you on the fully indexed rate, not the teaser. Option ARMs (negative amortization) are essentially gone. A modern 7/1 ARM on a prime-credit borrower is a much safer product than a 2/28 subprime ARM from 2006. But the underlying math — you assume interest rate risk in exchange for a teaser discount — is the same.

A concrete example: 7/1 ARM on a $450,000 loan

Teaser: 5.75% for 7 years. Fixed alternative: 6.75%. Cap structure: 2/1/5.

During the 7-year teaser, ARM payment is $2,625/month vs. $2,918 fixed. Monthly savings: $293. Seven-year total: $24,612 saved.

At year 8, worst case the rate jumps to 7.75% (teaser + 2% cap). Remaining balance about $400,500. New payment on a 23-year amortization: $3,091/month — $173 more than the fixed alternative you passed on.

If that rate sticks at the 7.75% cap for the rest of the loan, you pay $173/month over the fixed for 23 years = $47,748 of excess. Subtract the teaser savings of $24,612: you're net $23,136 worse off than if you'd taken the fixed. But you also got $24k of upfront flexibility — early-years cash flow when you may have needed it most.

If rates don't reach the cap (perhaps the Fed cuts, SOFR drops), your worst case doesn't materialize and you're ahead of the fixed borrower. This is the core ARM bet: you're betting against the cap scenario materializing.

When to consider an ARM in 2026

The current environment (early 2026) has fixed rates around 6.5–7% and ARMs around 5.5–6%. That's roughly a 0.75–1% spread, which is within historical norms. If you're buying a home you plan to sell in 4–6 years, a 7/1 ARM is defensible. If you plan to stay 10+ years, fixed is almost certainly the better call unless you have strong views on rate direction.

The wild card is whether rates fall over the next 5 years. Forward curves as of this writing imply 1–1.5% of Fed cuts between now and 2029. If that plays out, an ARM taken today might see its first reset come in belowthe teaser rate — the best-case scenario. But no one has a reliable crystal ball, and ARMs are designed to price in the lender's expected rate path.

Related tools

Run a full fixed-rate payment in our mortgage payment calculator. See what refinancing out of an ARM might look like in our refinance savings calculator. Make sure the teaser payment doesn't max your DTI using our DTI calculator.

ARM vs. fixed rate mortgage calculator