Key takeaways
- A fixed-rate mortgage keeps your principal and interest payment the same for the entire loan term.
- An ARM usually starts with a lower rate for a set period, then adjusts based on an index plus a margin, within caps.
- ARMs tend to make the most sense if you are confident you will sell or refinance before the first adjustment.
- A 15-year loan saves a lot of interest but has a much higher monthly payment than a 30-year loan.
In this guide
In the fixed vs adjustable rate mortgage decision, a fixed-rate loan locks your interest rate and principal-and-interest payment for the whole term, while an adjustable-rate mortgage (ARM) starts with a set rate for a few years, then changes periodically. Fixed rates offer predictability; ARMs may start lower but risk higher payments later.
This guide explains how each works, when an ARM can make sense, and how to think about 15- versus 30-year terms.
How a fixed-rate mortgage works
With a fixed-rate mortgage, the interest rate you lock at closing never changes. Your principal and interest payment stays the same for the life of the loan, whether that is 30, 20, 15 or 10 years. Your total monthly payment can still change if property taxes, homeowners insurance or mortgage insurance change, since those are often collected through escrow.
Early payments go mostly toward interest; over time, more of each payment goes to principal. This schedule is called amortization.
Fixed-rate loans are the most common choice because they are simple and protect you if market rates rise. The tradeoff is that the starting rate is often higher than an ARM's introductory rate, and if rates fall, you would need to refinance to benefit.
How an adjustable-rate mortgage works
An ARM has two phases:
- Initial fixed period. The rate is set for a number of years, commonly three, five, seven or ten.
- Adjustment period. After that, the rate resets on a schedule, often every six months or every year, for the rest of the term.
At each reset, your new rate equals an index plus a margin. The index is a published benchmark that moves with the market; many newer ARMs use the Secured Overnight Financing Rate (SOFR). The margin is a fixed number of percentage points set in your loan documents.
Understanding ARM rate caps
Caps limit how much your rate can move. They are usually written as three numbers, such as 2/1/5:
| Cap | What it limits | In a 2/1/5 example |
|---|---|---|
| Initial adjustment cap | Maximum change at the first reset | Up to 2 percentage points |
| Subsequent adjustment cap | Maximum change at each later reset | Up to 1 percentage point |
| Lifetime cap | Maximum increase over the starting rate for the life of the loan | Up to 5 percentage points |
Cap structures vary by loan, so read your Loan Estimate and ARM disclosures carefully.
Fixed vs adjustable: side-by-side comparison
| Feature | Fixed-rate mortgage | Adjustable-rate mortgage |
|---|---|---|
| Starting rate | Often higher | Often lower during the intro period |
| Payment stability | Principal and interest never change | Can rise or fall after the intro period |
| Risk if rates rise | None on your rate | Payment can increase up to the caps |
| Benefit if rates fall | Must refinance to capture it | Rate may drop at resets, subject to any floor |
| Complexity | Simple | Index, margin, caps and schedules to understand |
| Best for | Long-term owners, tight budgets | Shorter expected stays, higher risk tolerance |
When an ARM can make sense
An ARM is worth considering if:
- You are confident you will sell or move before the fixed period ends, for example due to a planned relocation.
- The initial rate is meaningfully lower than the fixed rate available to you.
- Your income is likely to rise, or you have the savings to absorb a higher payment.
- You understand and can afford the worst-case payment under the lifetime cap.
A fixed rate usually makes more sense if you expect to stay in the home for a long time, your budget has little slack, or you simply want certainty.
15-year vs 30-year mortgage terms
The loan term is a separate choice from the rate type, though fixed-rate loans are where you will most often compare terms. The two most common are 15 and 30 years.
| Factor | 15-year fixed | 30-year fixed |
|---|---|---|
| Interest rate | Usually lower | Usually higher |
| Monthly payment | Much higher | Lower |
| Total interest paid | Far less | Far more |
| Equity building | Fast | Slow in early years |
| Budget flexibility | Less | More |
The higher payment on a shorter term also raises your debt-to-income ratio, which can reduce how much house you can afford on paper.
A middle path
Some borrowers take a 30-year loan for its lower required payment, then pay extra toward principal when their budget allows. This will not match a 15-year loan's lower rate, but it shortens the payoff and cuts interest while keeping flexibility if money gets tight. Confirm your loan has no prepayment penalty and that extra payments are applied to principal.
How to decide
Ask yourself three questions:
- How long will I realistically keep this loan? Long horizons favor fixed rates.
- Could I handle the ARM's worst-case payment? If not, go fixed.
- Which monthly payment fits comfortably, with room for savings? That often decides 15 versus 30 years.
Whatever you choose, it applies to any of the main types of mortgages, and your mortgage preapproval is a good time to request quotes on both structures.
The bottom line
Choose a fixed rate if you want a payment that never changes and plan to stay for years. Consider an ARM only if the savings are real, your timeline is short, and you can afford the capped worst case. For term length, a 15-year loan saves the most interest, while a 30-year loan protects your monthly cash flow.
Frequently asked questions
Is it better to get a fixed or adjustable rate mortgage?
Neither is better for everyone. A fixed rate suits buyers who plan to stay put for many years and value a predictable payment. An adjustable rate can save money if its starting rate is meaningfully lower and you expect to move or refinance before it adjusts. If a rate increase would strain your budget, a fixed rate is usually the safer choice.
What does 5/1 or 7/6 ARM mean?
The first number is how many years the introductory rate stays fixed. The second tells you how often the rate adjusts afterward. In a 5/1 ARM the rate can change once a year after five years, while in a 7/6 ARM it is fixed for seven years and then can change every six months. Many newer ARMs use six-month adjustments.
Can an adjustable rate go down?
Yes. When an ARM adjusts, the new rate is based on the current value of its index plus the margin, so if the index has fallen, your rate and payment can drop. Many loans set a floor, often equal to the margin, below which the rate cannot fall. Check your loan documents to see the floor and caps that apply.
Should I get a 15-year or 30-year mortgage?
A 15-year mortgage typically has a lower interest rate and builds equity much faster, cutting total interest dramatically, but the monthly payment is considerably higher. A 30-year loan keeps payments lower and more flexible. Some borrowers choose a 30-year loan and make extra principal payments when they can, keeping the option to fall back to the required payment.
Official Resources & Further Reading
Use these resources to check current guidance. Requirements and availability may vary by state and provider.
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