Short answer: choose the fixed-rate mortgage if you plan to stay put for a decade or more, or if you simply value knowing your payment will never change. Choose an ARM only if you will realistically sell, refinance, or pay off the loan before the initial fixed period ends — and only when the starting-rate discount is big enough to justify the reset risk. In October 2026, with 30-year fixed rates near 7.4%, that discount can be close to a full percentage point, which is why ARMs are back in the conversation.
How a fixed-rate mortgage works
A fixed-rate mortgage locks your interest rate — and therefore your principal-and-interest payment — for the entire term. Thirty years is the standard; fifteen years is the equity-building alternative. Everything is known on day one: the payment, the total interest, the exact payoff date. That certainty has a price: fixed rates almost always run higher than an ARM’s introductory rate, because the lender absorbs all the rate risk.
How an ARM actually works
An adjustable-rate mortgage has two phases. During the initial fixed period (5, 7, or 10 years), the rate does not move. After that, the rate resets on a set schedule — every six months for the now-standard 5/6 and 7/6 ARM structures (the first number is the fixed-period years, the second is the months between adjustments).
Three numbers control what happens at reset:
- The index. Most conforming ARMs today are indexed to SOFR, a short-term benchmark that tracks the Federal Reserve’s policy rate.
- The margin. A fixed percentage your lender adds to the index, typically 2–3 points.
- The caps. The initial cap (max jump at the first adjustment, commonly 2 points), the periodic cap (max change at any later adjustment, commonly 1 point), and the lifetime cap (the ceiling over the starting rate, commonly 5 points). Confirm them in writing before you lock.
The honest part: your future rate depends on where short-term rates sit years from now. In September 2026 the Fed raised its benchmark rate for the first time in three years, a reminder that nobody can reliably predict your reset rate.
What the rate gap looks like right now
In early October 2026 the gap was roughly 0.5–1.0 points: about 7.44% for the average 30-year fixed versus roughly 6.97% for a 5/1 ARM in national survey data. Borrowers have noticed — ARMs rose to 10.3% of mortgage applications by early October, their highest share in a year. Today’s ARMs also look structurally safer than the pre-2008 generation: underwriting is stricter, and five-plus-year fixed periods mean nobody faces a payment shock in month thirteen.
Verified example: $400,000 at 7.44% vs 6.50%
A $400,000 30-year loan at 7.44% fixed (roughly the early-October national average) versus a 5/6 ARM starting at 6.50% — a 0.94-point spread, in line with recent survey data. All numbers were computed directly from the amortization formula:
| Metric | 30-year fixed (7.44%) | 5/6 ARM (6.50% intro) |
|---|---|---|
| Monthly principal & interest | $2,780.44 | $2,528.27 |
| You save per month (years 1–5) | — | $252.17 |
| Total saved over 5 years | — | $15,130.22 |
| Interest paid in first 5 years | $145,070.25 | $126,140.24 |
| Principal repaid in 5 years | $21,756.29 | $25,556.09 |
| Balance after 5 years | $378,243.71 | $374,443.91 |
| Payment after first reset (worst case, +2 pts → 8.50%) | $2,780.44 (never changes) | $3,015.12 (+$234.68 vs fixed) |
Three takeaways:
- The ARM’s early savings are real. $15,130 less in payments over five years, plus about $3,800 more equity built, since less of each early payment goes to interest.
- The worst case is not far away. If the first adjustment hits the full 2-point periodic cap (8.50%, re-amortized over 25 years), the ARM payment jumps to $3,015.12 — $235 a month above the fixed-rate payment. Those are guardrails, not forecasts — but they are the guardrails you accept.
- The breakeven is the fixed period. Sell or refinance before year five and the ARM wins. Every year past the reset, the math depends on what rates actually do.
Run your own numbers on our Mortgage Calculator or our Loan Amortization Calculator, and if a seller concession is on the table, compare it against the ARM discount with our Rate Buydown Calculator.
Who should pick which
Choose the fixed rate if: you plan to stay 10+ years, a surprise $200+ payment increase would strain your budget, or you simply sleep better with a number that never moves.
Choose the ARM if: you will sell before the fixed period ends (relocation, starter home), you have a concrete refinance plan (not just hope), the introductory discount is at least half a point, and you could absorb the worst-case reset payment without distress.
The refinancing fallacy
The most dangerous ARM math assumes a refinance that has not happened. “I’ll just refinance before the reset” is a prediction about future rates, future home values, and your future creditworthiness — and in 2026 borrowers watched rates rise, not fall. Take the ARM for the savings you can see in the fixed period, not for a rescue you cannot guarantee.
Related reading: FHA vs Conventional Loan, How Much Is PMI Per Month?, and How Much House Can I Afford on a $100k Salary?. The Consumer Financial Protection Bureau (consumerfinance.gov) publishes a plain-language guide to adjustable-rate mortgages, and the Federal Reserve (federalreserve.gov) publishes the rate data behind these figures.
Frequently asked questions
What is a 5/6 ARM, and is it the standard now?
A 5/6 ARM is an adjustable-rate mortgage with a 5-year initial fixed-rate period, after which the rate adjusts every 6 months. Yes — the “5/6” and “7/6” structures have replaced the older 5/1 and 7/1 products as the standard conforming ARM format, because the underlying benchmark switched from LIBOR to SOFR.
How much lower is an ARM rate than a fixed rate in 2026?
In early October 2026 the gap was roughly 0.5–1.0 percentage points: about 7.44% for the average 30-year fixed versus roughly 6.97% for a 5/1 ARM in national survey data. The MBA’s early-September survey showed a wider spread of about one point (6.85% vs 5.82%). The gap moves daily, so compare your actual quotes, not averages.
Can I refinance an ARM into a fixed-rate mortgage?
Yes — an ARM can be refinanced into a fixed-rate loan at any time. But do not take an ARM assuming a cheap refinance will be waiting at reset. Rates, home values, and your credit could all be worse, so model the worst-case reset payment as if no refinance happens.
What is the biggest risk of an ARM?
Payment shock at reset. After the fixed period, the rate can rise to the caps — on a $400,000 loan the worst-case payment can land several hundred dollars a month above the original. The risk is manageable with a long fixed period, tight caps, and an exit before reset, but it is the entire price of the introductory discount.