Fixed vs. Adjustable Mortgage Rates: A Plain Comparison
The choice between a fixed-rate and an adjustable-rate mortgage comes down to a single question: who carries the risk that interest rates change after closing. With a fixed rate, the lender and the borrower both know the rate for the life of the loan. With an adjustable rate, the rate can move, and the borrower carries that uncertainty in exchange for a different starting point. This comparison draws on pages from the Consumer Financial Protection Bureau (CFPB) and the U.S. Department of Housing and Urban Development (HUD). It deliberately includes no current market rates, because the sources fetched for this article do not give dated rate figures.
How the two loan types are defined
The CFPB’s fixed-rate mortgage explainer puts it directly: with a fixed-rate loan, “the interest rate is set when you take out the loan and will not change.” The principal and interest portion of the monthly payment is therefore predictable from the first day.
An adjustable-rate mortgage, or ARM, works differently. According to the CFPB’s ARM explainer, the rate may go up or down. Many ARMs begin with a rate lower than a comparable fixed-rate loan, and that starting rate may hold for months, one year or a few years. After the introductory period, the rate changes at regular intervals, and the payment is likely to rise.
The page advises borrowers not to assume they will sell or refinance before the rate changes, noting that property values or personal finances could shift in the meantime. The same caution recurs across the CFPB’s ARM material.
Index, margin and the mechanics of adjustment
An ARM’s rate after the introductory period has two parts. The index is a broader measure of interest rates, and the margin is a fixed number of percentage points the lender adds. In the CFPB’s wording, “The margin is a number of percentage points added to the index by the lender that sets your interest rate.” When the index rises, the payment generally rises with it. When the index falls, the payment may fall, but the CFPB notes that this is not true for every ARM.
HUD’s page on FHA adjustable-rate mortgages breaks an ARM into four components: the index, the margin, the structure of the interest rate caps, and the initial interest rate period. It says lenders disclose the margin at application and that margins vary by lender, which makes the margin a point of comparison between offers even when the starting rates look alike. For FHA-insured ARMs, HUD lists the Constant Maturity Treasury, a weekly average yield on U.S. Treasury securities adjusted to a one-year constant maturity, as an index.
Hybrid ARMs and what the labels mean
Many ARMs combine a fixed period with an adjustable one. The CFPB’s Consumer Handbook on Adjustable-Rate Mortgages, a booklet dated January 2014 and technically updated by the CFPB, explains the labels. In an X/Y format, the first number is the length of the fixed period and the second is how often the rate adjusts afterward, so a 3/1 loan is fixed for three years and then adjusts yearly. The booklet also mentions 5/1, 7/1 and 10/1 versions.
HUD’s FHA program follows a similar structure. Its page describes a standard 1-year ARM and four hybrid products with an initial fixed period of 3, 5, 7 or 10 years, after which the rate adjusts annually.
Because the booklet is dated 2014, its index examples should be checked against the disclosures for any current loan. The explanation of the labels is the part that carries forward.
Rate caps
Caps are the main protection built into an ARM, and the CFPB’s page on how rate caps work (last reviewed January 14, 2025) describes three kinds.
- Initial adjustment cap. Limits the change at the first adjustment after the fixed period; common values are 2 percent or 5 percent.
- Subsequent adjustment cap. Limits the change at each later adjustment; most commonly one or two percent.
- Lifetime cap. Limits the total change over the life of the loan; most commonly 5 percent, though some loans have a higher one.
Some loans also set a floor, meaning a different limit on decreases than on increases. The CFPB advises comparing caps and not only starting rates, since two lenders can offer the same initial rate with different caps. It also suggests asking the lender to calculate the highest payment the borrower may ever have to pay.
HUD’s FHA cap structures are specific. For FHA 1-year and 3-year ARMs, the rate can move up to 1 percentage point annually and 5 points over the life of the loan. For 5-year ARMs, the page lists either 1 point annually and 5 over the life, or 2 annually and 6 over the life. For 7-year and 10-year ARMs, the limits are 2 points annually and 6 over the life. Those figures apply to the FHA program, and conventional loans may use different structures, so the Loan Estimate for any given loan is the document that controls.
Payment shock, shown with an example
The 2014 CFPB booklet includes a worked example of what a rate increase does to a payment. A discounted 4 percent rate produced a first-year payment of $954.83. If the rate rose to a 6 percent fully indexed level, the payment became $1,192.63, and at 7 percent it reached $1,320.59. The loan amount is not restated in the summary used here, so the example is best read as a demonstration of the pattern and not a prediction for any particular loan.
The booklet separates this from other kinds of payment jump. Interest-only periods that end, and payment-option recasts, can produce sharp increases even when the rate itself does not change. It also warns of negative amortization, where the balance grows because payments do not cover all the interest.
The booklet also notes that the servicer must warn a borrower at least seven months before the first adjustment and at least 60 days before a new payment takes effect. Lenders must generally assess ability to repay using the fully indexed rate or the highest rate expected in the first five years, according to the same document.
Comparing offers fairly
A direct comparison of the interest rate on a fixed loan and on an ARM can be misleading. The CFPB’s page on the difference between a mortgage interest rate and the APR (last reviewed August 28, 2026) explains that the interest rate is the yearly cost of borrowing without fees, while the annual percentage rate, or APR, includes points, broker fees and other charges and is usually higher. On a Loan Estimate, the interest rate appears on page 1 under “Loan Terms,” and the APR appears on page 3 under “Comparisons.”
For ARMs, the CFPB states that the APR does not reflect the loan’s maximum interest rate. Comparing the APRs of fixed-rate and adjustable-rate loans, or of different ARMs, can therefore mislead, and the agency advises against choosing a loan on APR alone. The 2014 booklet takes a similar line, saying APRs should be compared only between similar ARMs.
The CFPB’s rate-caps page adds that the Loan Estimate or Truth-in-Lending disclosure also shows the highest possible payment, and that lenders must provide the disclosure within three business days after a borrower applies.
Time horizon and the refinance assumption
Two ideas from the sources keep returning when the decision is framed around time. The first is HUD’s observation that an ARM may suit a borrower who expects to own the home only a few years. The second is the CFPB’s warning against counting on a sale or refinance before the first adjustment. Those two statements pull in different directions, and the tension is the core of the fixed-versus-adjustable question.
A fixed rate removes the need to forecast either rates or life events, at the price of a starting rate that may be higher. An adjustable rate rewards a correct forecast of a short ownership period and exposes a borrower whose plans change. The CFPB checklist for ARMs, which asks how high payments could go, when the first increase could happen and whether the maximum payment would still be affordable, is a way of testing the downside before committing.
The CFPB’s ARM explainer was last reviewed on January 14, 2025, and its page shows a modification date of May 21, 2026. The rate-cap figures above come from the January 2025 review.
Questions the sources suggest asking
- How high and how low can the rate and payment go at each adjustment?
- How often does the rate adjust, and when could the first payment increase occur?
- Are there caps and floors, and do they differ for the first adjustment?
- Could the payment still be afforded at the maximum allowed rate?
- How long is the home likely to be owned, and could the loan be converted to a fixed rate, and at what fee?
- Does the loan allow negative amortization, interest-only payments or a balloon payment?
HUD’s page offers its own framing of who an ARM may suit: borrowers who plan to own the home for only a few years, who expect higher future earnings, or who face high prevailing fixed rates. That is HUD’s description of the product, and not a recommendation for any individual.
Where to get help
The CFPB booklet directs borrowers to HUD-approved housing counselors, reachable through the CFPB’s find-a-counselor tool or at 800-569-4287, and gives (855) 411-CFPB (2372) for complaints. The rate-caps page repeats the CFPB number for connecting with a HUD-approved counselor.
Related reading
Other guides cover getting pre-approved for a mortgage in New York, questions to ask a lender about locking a rate, and reading a closing disclosure in New York.
This article is general information and is not legal or financial advice.
Rules, rates, fees and procedures change; confirm current details with the official sources linked above and with a licensed attorney or other qualified professional before making decisions.
