A fixed-rate mortgage holds the same rate for the full loan term; an adjustable-rate mortgage (ARM) starts lower and resets after a fixed period of 5, 7, or 10 years. Freddie Mac's Primary Mortgage Market Survey shows the spread between the two commonly running 0.75 to 1.5 percentage points -- roughly $200 to $400 per month on a $400,000 loan.
How a Fixed-Rate Mortgage Works
A fixed-rate mortgage sets your interest rate at closing and holds it there for the full loan term -- typically 15 or 30 years. Your principal and interest payment is the same in month one as it is in month 359. The only components of your monthly housing expense that change over time are property taxes (which adjust with assessed value) and homeowners insurance (which adjusts at renewal). The mortgage payment itself is locked.
This predictability has a mechanical cause. Fixed-rate loans are priced against U.S. Treasury yields, particularly the 10-year note. The amortization schedule is set at closing and front-loads interest -- in the early years of a 30-year loan, most of each payment covers interest rather than principal; by year 15, that ratio has shifted substantially in favor of principal. The schedule does not change.
According to Freddie Mac's Primary Mortgage Market Survey, the weekly average rate on a 30-year fixed-rate mortgage ranged from 6.0 to 7.5 percent over the 12-month period ending in early 2026, depending on credit profile and loan-to-value ratio. The 15-year fixed typically runs 0.5 to 0.75 percentage points below the 30-year, also per Freddie Mac, but requires a higher monthly payment because the same balance is retired in half the time.
Key takeaway
The fixed rate you lock at closing is the rate you pay forever, regardless of what happens to market rates afterward. If rates fall, you keep your higher rate unless you refinance (at a cost). If rates rise, you keep your lower rate at no action required.
How an ARM Works: Index, Margin, and Caps
An adjustable-rate mortgage (ARM) has two distinct phases: an initial fixed period during which the rate does not change, and an adjustment phase during which the rate resets periodically based on a formula.
The formula: index plus margin.
Your ARM rate during any adjustment period equals a published market index plus your lender's margin. The margin is set at origination and does not change -- it is a lender-specific spread, commonly 2.5 to 3.0 percentage points above the index, according to the Consumer Financial Protection Bureau. The index is a short-term benchmark rate that moves with market conditions. The most commonly used index today is the Secured Overnight Financing Rate (SOFR), which replaced LIBOR as the dominant ARM benchmark. When SOFR rises, your rate rises by an equal amount at the next adjustment, subject to caps. When SOFR falls, your rate falls.
Caps: how far the rate can move.
Every conforming ARM sold in the United States carries three types of caps, per Fannie Mae guidelines:
- Initial adjustment cap. The maximum the rate can rise (or fall) at the first adjustment after the fixed period ends. Commonly 2 percentage points for loans with fixed periods of five years or more.
- Periodic adjustment cap. The maximum the rate can change at any single subsequent adjustment. Most commonly 2 percentage points per adjustment.
- Lifetime cap. The maximum the rate can ever rise above the initial note rate over the entire loan life. Most commonly 5 percentage points.
A 5/1 ARM starting at 5.5 percent with a standard 2/2/5 cap structure can rise no higher than 7.5 percent at its first adjustment, no more than 2 additional points at any later adjustment, and no higher than 10.5 percent ever. That ceiling is real protection -- but it also describes a scenario in which your payment increases substantially.
The 5/1, 7/1, and 10/1 ARM: What the Numbers Mean
The naming convention for ARMs is straightforward once you understand it. The first number is the length of the initial fixed period in years. The second number is the frequency of adjustments after that period ends, also in years.
5/1 ARM. Fixed for 5 years, then adjusts once per year. The shortest fixed window among the three common structures -- and typically the one with the lowest initial rate. Appropriate only if you have high confidence that you will sell or refinance within the fixed period.
7/1 ARM. Fixed for 7 years, then adjusts once per year. Offers a wider margin before the first adjustment compared with the 5/1, at a slightly higher initial rate. For buyers who are confident about a 5-to-6-year hold but want a small buffer, the 7/1 provides it.
10/1 ARM. Fixed for 10 years, then adjusts once per year. The initial rate is typically the closest to a 30-year fixed among the three structures, but still usually below it. If your actual hold period is 8 to 12 years, the 10/1 deserves a side-by-side calculation against the 30-year fixed. The rate advantage may be modest enough that the fixed product is the more rational choice.
Across all three structures, the rate advantage over a 30-year fixed narrows as the fixed period lengthens. According to Freddie Mac's Primary Mortgage Market Survey, the spread between a 30-year fixed and a 5-year ARM has historically ranged from 0.5 to 1.5 percentage points, with wider spreads appearing during periods of steep yield curves and narrower spreads when the yield curve is flat or inverted.
The rate gap matters because it determines how much you actually save during the fixed period -- and whether those savings offset the risk of a higher rate afterward.
Tip
Before choosing a specific ARM product, calculate the total interest you would pay over your expected hold period under both the ARM (at its initial rate) and the 30-year fixed. If the fixed-rate product costs only marginally more over your realistic hold period, the rate certainty is usually worth it.
When an ARM Can Make Financial Sense
An ARM is not inherently riskier than a fixed mortgage in every situation -- it is a tool that suits specific scenarios. The conditions under which it makes rational sense are narrower than lenders sometimes suggest, but they are real.
You expect to sell within the fixed window. If you are relocating for work with a defined five-year horizon, a 5/1 ARM lets you take the lower rate without accepting adjustment risk -- because you plan to exit before the first reset. This logic holds only if the exit plan is disciplined and not contingent on market conditions that may not cooperate.
The monthly savings are material, not marginal. A 0.25-point rate gap yields modest savings over five years -- modest enough that a fixed rate's certainty is usually worth the small premium. When the spread reaches 1.0 to 1.5 percentage points, which occurs during steep yield curves, annual savings can be several thousand dollars, which changes the calculation.
You have financial flexibility to absorb a reset. Borrowers who have significant liquid assets, stable income, and a realistic refinancing option if rates rise are better positioned to carry an ARM into its adjustment phase without severe impact. The CFPB recommends that ARM borrowers model their budget at the maximum possible rate after the first adjustment, not just the initial rate, before committing to the product.
Rates are elevated and forecasters expect declines. When fixed rates are high relative to long-run averages, an ARM lets a borrower capture declining rates automatically during the adjustment phase. This scenario requires accepting that rate movements are uncertain -- which no borrower or lender can predict reliably.
For buyers who finance the down payment strategy carefully, an ARM's lower initial payment can free up cash for reserves or principal paydown during the fixed window.
The Risk Scenarios: What Payment Shock Looks Like
Payment shock is the term used by the CFPB and mortgage regulators to describe the sudden increase in a borrower's monthly payment when an ARM resets to a higher rate. It is not a hypothetical -- it is the mechanism the product was designed around, subject only to the cap limits. Borrowers who understand it in advance can plan for it; borrowers who are surprised by it are the ones who default.
Consider a borrower who takes a 5/1 ARM at 5.5 percent on a $400,000 30-year mortgage. The initial principal and interest payment is approximately $2,271 per month.
After five years, the loan balance is approximately $370,000. If the index has risen and the first adjustment moves the rate to 7.5 percent (initial cap of 2 percentage points), the new payment on the remaining 25-year term is approximately $2,738 per month -- a jump of $467. If the rate hits the periodic cap again at year six (9.5 percent), the payment becomes approximately $3,224 -- an increase of $953 from the original payment.
Neither scenario is the worst case. At the 10.5 percent lifetime cap, the payment on that same remaining balance would be approximately $3,730 -- a $1,459-per-month increase from the initial payment.
Warning
Model your ARM at the first-adjustment cap, not the initial rate, before deciding whether you can afford the payment. A $400 monthly increase sounds abstract until it represents 15 to 20 percent of your take-home pay. If your budget cannot absorb the capped payment, the ARM is not the right product regardless of the initial savings.
The scenario is not inevitable -- many ARM borrowers sell or refinance before the first adjustment as planned. But plans change. Job losses, divorces, market downturns, and health emergencies occur at unpredictable times. Taking an ARM on the assumption that your exit plan will execute on schedule means accepting that none of those events will happen during the critical window.
The comparison table below summarizes how fixed-rate and ARM mortgages differ across the dimensions that matter most to a buyer's decision.
| Feature | 30-Year Fixed | 5/1 ARM |
|---|---|---|
| Rate stability | Locked for life of loan | Fixed 5 years; variable after |
| Initial rate | Higher (30-yr benchmark) | Lower by 0.5-1.5 pts typically |
| Payment predictability | Identical every month | Changes after fixed period |
| Risk exposure | None post-closing | Rate and payment risk at each reset |
| Best for | Long-term holds (7+ years), stability-focused buyers | Short confirmed hold periods, flexible financial position |
| Payment shock risk | None | Material if rates rise before first reset |
| Refinancing required to lower rate | Yes | No -- rate falls automatically if index falls |
Accurate interest in each scenario always depends on your actual loan size, current market rates at the time of application, credit score, and loan-to-value ratio. For a personalized picture, the CFPB's consumer tools at consumerfinance.gov include an ARM explainer that lets you model adjustments against actual SOFR values.
How to Decide: A Framework for Your Situation
The decision between a fixed-rate mortgage and an ARM comes down to four questions. None of them require a prediction about future interest rates -- which no one can make reliably. They require honest answers about your own situation.
How long will you realistically hold this property?
This is the most important question. If you are buying a starter home and expect to upsize within five to seven years, the math on a 5/1 or 7/1 ARM often works in your favor during the fixed window. If you are buying a home you intend to keep for 15 or 20 years, locking in a fixed rate eliminates interest rate risk for the entire period.
That word "realistically" carries weight. Many borrowers expect to move in five years and find themselves in the same property at year ten because the market moved against them or selling became less attractive. Build in a buffer: if you think you will sell in seven years, model as if you will stay ten.
Can your budget absorb the first-adjustment cap payment?
Run the numbers. Take your ARM's initial rate plus 2 percentage points (the standard initial adjustment cap), apply it to your projected loan balance at the end of the fixed period, and calculate the new payment on the remaining term. If you cannot cover that payment within the rest of your budget without stress, the ARM is not the right product. This is not a worst-case scenario -- it is the product working exactly as disclosed.
What will closing costs do to your refinancing option?
The ARM-into-refinance strategy assumes refinancing is available before the first adjustment. Refinancing costs money -- according to Freddie Mac, typically 2 to 5 percent of the loan amount. If equity has eroded or rates have risen, it may cost more than it saves. Factor closing costs into your ARM plan as a liability, not a given.
Is the rate spread wide enough to justify the risk?
If the 30-year fixed rate is 6.5 percent and the 5/1 ARM is 6.25 percent, the monthly savings on a $400,000 loan is roughly $65 -- about $3,900 over five years. Against the risk of a capped first-adjustment increase that could cost hundreds per month, that spread is not compelling. Spreads above 0.75 to 1.0 percentage points are worth modeling carefully; spreads below that typically favor the fixed product.
Warning
Do not choose an ARM because the initial payment makes an otherwise unaffordable purchase feel manageable. The CFPB advises qualifying for any ARM at the maximum possible rate, not the initial rate, for exactly this reason. A lower payment that lasts five years and then becomes unaffordable is not affordability -- it is a deferred problem.
For buyers still working through whether they are ready to commit to a purchase at all, the rent-vs-buy calculation is the right starting point before the fixed vs. ARM question even applies. And if you are weighing loan structure against down payment tradeoffs, see how different loan types affect your down payment requirement -- the loan type shapes both the rate you can access and the upfront cash you need.
The mortgage structure question has no universal answer. What it has is a set of numbers specific to your loan, your timeline, and your financial position -- and those numbers can be calculated before you sign anything.
Frequently asked questions
What is the difference between a fixed-rate and an ARM mortgage?
A fixed-rate mortgage keeps the same interest rate for the entire loan term -- 15 or 30 years -- so your principal and interest payment never changes. An adjustable-rate mortgage starts with a fixed period (often 5, 7, or 10 years), then resets periodically based on a market index. Fixed rates offer certainty; ARMs offer a lower initial rate with future uncertainty.
When does an ARM mortgage make sense?
An ARM can be worth considering when you are confident you will sell or refinance before the fixed period ends -- typically within five to seven years. It may also make sense when the rate gap between the ARM and a 30-year fixed is large enough to meaningfully reduce your monthly payment during the fixed window. Verify your exit timeline is realistic before choosing an ARM.
What is payment shock on an ARM mortgage?
Payment shock is the sudden increase in your monthly mortgage payment when an ARM's rate adjusts upward after the fixed period. If rates rise significantly before your first adjustment, your payment can jump several hundred dollars per month. Per-adjustment and lifetime caps limit how far the rate can move, but they do not eliminate the risk of a substantially higher payment.
What does 5/1 ARM mean?
A 5/1 ARM has a fixed interest rate for the first five years, then adjusts once per year afterward. The first number is the fixed period in years; the second is the adjustment frequency in years. A 7/1 ARM fixes the rate for seven years then adjusts annually; a 10/1 ARM fixes for ten years. The adjustment is calculated by adding the current index value to the lender's margin.
Can you refinance out of an ARM before it adjusts?
Yes. Many borrowers take an ARM specifically intending to refinance before the fixed period expires. Whether that strategy works depends on your credit profile and home equity at refinance time, current market rates, and closing costs -- which according to Freddie Mac typically run 2 to 5 percent of the loan amount. A rate environment higher than today's could make refinancing more expensive, not less.