Choosing between a fixed-rate mortgage and an adjustable-rate mortgage (ARM) is one of the most important decisions you will make as a borrower. The choice affects your monthly payment, your long-term interest cost and how much risk you take on if interest rates change. This guide explains how each loan works, compares them with examples and helps you decide which one fits your situation.
How a Fixed-Rate Mortgage Works
With a fixed-rate mortgage, your interest rate stays the same for the entire life of the loan. The most common terms are 30 years and 15 years. Your principal and interest payment never changes, which makes budgeting simple. Property taxes and insurance may still rise, so your total monthly housing payment can change even though the interest rate does not.
Pros of Fixed-Rate Loans
- Predictable payments for the life of the loan.
- Protection from rising rates.
- Simplicity, since there are fewer terms to track.
- Easy planning for long-term budgets.
Cons of Fixed-Rate Loans
- Higher starting rate than most ARMs.
- No benefit if rates fall, unless you refinance, which costs money.
- Higher payments on shorter terms like 15 years, though total interest is lower.
How an Adjustable-Rate Mortgage Works
An ARM starts with a fixed introductory rate for a set period, then adjusts periodically based on a market index plus a margin. Common ARMs are described with two numbers. A 5/6 ARM has a fixed rate for five years, then adjusts every six months. A 7/6 ARM is fixed for seven years. Older products described as 5/1 ARMs adjust annually.
ARMs include caps that limit how much the rate can change:
- Initial adjustment cap. The most the rate can rise the first time it adjusts.
- Periodic adjustment cap. The most it can change at each later adjustment.
- Lifetime cap. The highest the rate can ever go above the starting rate.
For example, a 5/6 ARM with 2/1/5 caps could rise up to 2 percentage points at the first adjustment, 1 point at later adjustments and 5 points in total above the initial rate.
Pros of ARMs
- Lower initial rate and payment.
- Good fit for short-term owners who plan to sell or refinance before the adjustment.
- Potential savings if rates fall.
Cons of ARMs
- Payment shock if rates rise.
- Harder to budget after the fixed period.
- Complexity, including indexes, margins and caps.
- Refinance risk, since you might not qualify or rates might not be favorable later.
Side-by-Side Comparison
| Feature | Fixed-rate | Adjustable-rate |
|---|---|---|
| Rate | Constant | Fixed, then adjusts |
| Starting payment | Higher | Usually lower |
| Risk of payment increase | None for principal and interest | Possible after fixed period |
| Best for | Long-term owners, budget certainty | Short-term owners, risk-tolerant buyers |
| Complexity | Low | Higher |
A Simple Example
Imagine a $320,000 loan. A 30-year fixed loan at 6.5 percent has a principal and interest payment of about $2,022. A 7/6 ARM might start at 6.0 percent, with a payment near $1,919, saving roughly $100 a month for seven years, or about $8,700. But if the rate adjusts upward by 2 points to 8.0 percent after year seven, the payment could climb above $2,300 on the remaining balance. The ARM wins if you sell or refinance before the adjustment and loses if you stay and rates climb. These numbers are illustrations; get real quotes from lenders.
How to Decide
Ask yourself these questions:
- How long will I stay in the home? If fewer than seven years, an ARM may save money.
- How stable is my income? If you have little room for payment increases, choose fixed.
- What is my risk tolerance? If rate changes would cause stress, choose fixed.
- What is the rate difference? If the ARM discount is small, the risk may not be worth it.
- Could I handle the worst case? Calculate the payment at the lifetime cap.
- Do I expect income growth? A growing income can make payment risk more manageable.
What About 15-Year vs. 30-Year Fixed?
A 15-year fixed has a lower rate and much lower total interest but a higher monthly payment. A 30-year loan gives flexibility. Some borrowers take a 30-year loan and make extra principal payments voluntarily. Use our guide to how much house you can afford to test what monthly payment fits your budget.
When Refinancing Enters the Picture
Some buyers choose an ARM expecting to refinance into a fixed loan later. That can work, but it is a bet. If your credit worsens, your home value drops or rates rise, you may not be able to refinance on good terms. Learn how to evaluate that choice in our guide to refinancing your mortgage.
Tips for Comparing Loans
- Ask for Loan Estimates from several lenders.
- Compare the APR as well as the interest rate.
- Read the ARM disclosures, including the index, margin and caps.
- Ask about prepayment penalties.
- Check your credit first so you qualify for the best offer. See improving your credit score.
The Consumer Financial Protection Bureau explains ARM features and has a helpful booklet at consumerfinance.gov.
Ask About Points and Buydowns
Some lenders let you pay discount points to lower your rate, or offer temporary buydowns that reduce your rate for the first year or two. A temporary buydown can look like an ARM but ends with a fixed rate afterward, so you should compare them carefully. Calculate the break-even period for any points, which is the time it takes for monthly savings to pay back the upfront cost. If you might move or refinance before then, points may not be worth it.
Stress-Test Your Budget
Whichever loan you pick, test your budget at a higher payment. For an ARM, calculate your payment at the maximum rate allowed by the caps. For a fixed loan, add a buffer for property tax and insurance increases. If the stressed payment would make saving impossible, consider a smaller loan or a longer horizon before buying.
Frequently Asked Questions
Are ARMs risky?
They carry more risk than fixed loans because payments can rise, but caps limit the increase and many borrowers use them successfully for short-term ownership.
What index do ARMs use?
Most newer ARMs use the Secured Overnight Financing Rate (SOFR) or a similar benchmark, plus a margin.
Can I convert an ARM to fixed?
Some loans include a conversion option, usually with a fee. Otherwise you would need to refinance.
Which is better when rates are high?
Some borrowers choose an ARM hoping to refinance if rates fall, but remember that is not guaranteed.
Bottom Line
A fixed-rate mortgage offers certainty, while an ARM offers a lower starting payment in exchange for risk. Choose based on how long you will stay, how much payment risk you can handle and how large the rate difference is.
Related guides
- Should You Refinance Your Mortgage? The Break-Even Math
- How Much House Can I Afford? A Realistic Budget Guide
- Balance Transfer Credit Cards: How They Work and When to Use One
- Term vs. Whole Life Insurance: Which One Fits Your Family?
This article is for general education only and is not financial, tax, legal or insurance advice. Rates, limits and rules change, so confirm current details with the provider or a licensed professional before you decide.