Fixed- vs. adjustable-rate mortgage (ARM): What’s the difference?

Written by Samantha SheltonNMLS 1647301Updated September 2026

Couple weighing two homes in a Michigan neighborhood while deciding between a fixed-rate mortgage and an ARM

A fixed-rate mortgage locks one interest rate for the entire term, usually 15 or 30 years, so your principal-and-interest payment never changes. An adjustable-rate mortgage (ARM) holds a lower introductory rate for a set period, commonly 5, 7 or 10 years, then resets on a schedule tied to an index plus a fixed margin: in the CFPB’s own sample 5/1 ARM disclosure, a 3% starting rate can climb to 8% and a $910.66 principal-and-interest payment can reach $1,467 by year 8.¹

The real difference is where interest-rate risk sits. On a fixed loan the lender carries it; on an ARM you carry it once the introductory period ends, but only within limits printed on your paperwork before you sign. Page 2 of your Loan Estimate carries an Adjustable Interest Rate (AIR) table showing the index, the margin, the minimum and maximum rate, and the cap on each change.

Learn how fixed-rate and adjustable-rate mortgages differ on rate mechanics, cap structure and total cost, and which one matches how long you’ll keep the home. Still mapping the landscape? Start with our Loan Types & Programs guide or browse our other loan comparisons.

Key takeaways:

Fixed means one rate for 360 payments: On a 30-year fixed loan the principal-and-interest amount is identical in month 1 and month 360. Freddie Mac has published a weekly 30-year fixed average since April 1971.
The two numbers in an ARM’s name are the whole story: A 5/6m ARM is fixed for 5 years, then adjusts every 6 months; a 7/1 ARM is fixed for 7 years, then adjusts annually. The name says nothing about the caps or the index.
Your worst case is knowable before you sign: A 5/1 ARM starting at 6% under a common 2/2/5 cap structure can reach 8% at the first adjustment and 11% for the life of the loan. Ask for the payment at that ceiling.

What is a fixed-rate mortgage?

A fixed-rate mortgage is a home loan whose interest rate is set at closing and never changes, so the principal-and-interest portion of every payment is identical. Terms of 30, 20 and 15 years are the common choices. No index, no margin, no adjustment date, no cap table. The only thing that moves your total payment is escrow for property taxes and insurance.

What you’re buying is insurance against a market nobody can forecast. Freddie Mac’s Primary Mortgage Market Survey has tracked the average 30-year fixed rate weekly since April 1971, and the series peaked at 18.63% in 1981. A reminder that 30 years is long enough to contain conditions nobody at the closing table expected. Check Freddie Mac’s weekly average mortgage rates for where pricing sits now and the long-run history of 30-year fixed rates for the full sweep. Our breakdown of the benefits and drawbacks of fixed-rate loans covers what that certainty costs: a higher starting rate than an ARM borrower with the same file, and no automatic benefit if rates fall.

What is an adjustable-rate mortgage (ARM)?

An adjustable-rate mortgage is a home loan whose rate is fixed for an introductory period and then resets periodically to a published index plus a fixed margin, within caps set by your note. The CFPB’s Consumer Handbook on Adjustable-Rate Mortgages states the formula plainly: interest rate = index + margin. Three pieces do all the work:

The index moves and you don’t control it. Fannie Mae requires every eligible conventional ARM plan to use the 30-day average Secured Overnight Financing Rate (SOFR) published by the New York Fed. FHA permits the Constant Maturity Treasury index or 30-day average SOFR (24 CFR 203.49).
The margin is fixed for the life of the loan. It’s the lender’s spread over the index, disclosed on your Loan Estimate. It’s also a floor: an ARM’s rate may never fall below the margin, whatever a downward cap would allow.
The caps limit the damage. Every Fannie Mae ARM plan must offer both lifetime and per-adjustment rate change limitations, with the lifetime limit applying to increases only.

One index worth naming for what it no longer is: LIBOR. All U.S. dollar LIBOR panel settings ceased after June 30, 2023, and existing LIBOR-indexed ARMs moved to spread-adjusted SOFR replacement rates under the LIBOR Act. If a quote calls LIBOR a live index, the document is out of date.

Watch the gap between your start rate and the fully indexed rate. The CHARM booklet’s own example: a lender’s fully indexed rate is 4.5% (a 2% index plus a 2.5% margin), but the loan carries a 3% “teaser” start rate. Even if the index never moves, your rate rises to 4.5% when the introductory period ends. Our guide to what happens at an ARM reset covers that first adjustment.

Fixed vs. adjustable-rate mortgage: side-by-side comparison

Here is the decision in six rows. Read the last two first, they settle it more often than the rate.

Feature	Fixed-rate mortgage	Adjustable-rate mortgage (ARM)
Interest rate	One rate for the entire term, set at closing. It never changes.	Fixed for an introductory period, commonly 5, 7 or 10 years, then resets to index plus margin on a set schedule.
Payment stability	Principal and interest are identical across all 360 payments of a 30-year loan.	Identical during the introductory period, then recalculated at each adjustment.
Typical starting rate	Set the day you lock. Check the current national average before you shop.	Historically priced below the comparable fixed rate during the introductory period. That discount is why ARMs exist. The gap moves weekly.
Worst-case payment	Your starting payment is the worst case. Only escrow can raise it.	Knowable before you sign: the maximum rate and payment appear on page 1 of your Loan Estimate and in the AIR table.
Best fit	You’ll hold the loan past any introductory period, you’re on a fixed income, or you want the number to stop moving.	Your ownership horizon is shorter than the fixed period, and you could still afford the payment at the lifetime cap if it isn’t.
Refinance dependency	None. You refinance only when it saves you money.	Often built into the plan. The CFPB’s warning is explicit: don’t count on refinancing before your rate and payment increase.

How ARM caps work

Caps are three separate limits, usually written as three numbers such as 2/2/5 or 5/2/5. That shorthand is a market convention, not a rule. The actual limits are whatever your note says, which is why the AIR table exists.

Initial adjustment cap (first number): How far the rate can move at the first reset. A 2 means two percentage points; a 5 means five.
Subsequent adjustment cap (second number): How far it can move at each adjustment after that.
Lifetime cap (third number): The maximum total increase above your starting rate, however long you hold the loan.

Run the arithmetic and the worst case stops being abstract. Take a $300,000 loan, 30-year term, a 5/1 ARM starting at 6% with a 2/2/5 structure: fixed five years, then up to two points at the first adjustment, two at each one after, and never more than five points above 6%, an 11% ceiling.

Loan year	Rate	Principal & interest	What limits it
Years 1 – 5	6.000%	$1,799	Introductory fixed period.
Year 6	8.000%	$2,155	Initial adjustment cap: 2 points.
Year 7	10.000%	$2,528	Subsequent adjustment cap: 2 points.
Year 8 and after	11.000%	$2,718	Lifetime cap: 5 points over the 6% start.

That’s about $919 more per month than the starting payment, roughly 51% higher, and it takes three consecutive maximum increases to get there. Qualify yourself against that ceiling, not the introductory payment. An ARM whose ceiling you could absorb is a different product from one that would break you.

You do get warning. Under Regulation Z, your servicer must send the first-adjustment notice at least 210 but no more than 240 days before the first payment at the new level is due, seven to eight months of lead time, and later adjustments carry a 60-to-120-day notice (12 CFR 1026.20(c) and (d)). Your lender must also give you the CHARM booklet and a program disclosure when you apply (12 CFR 1026.19(b)).

How ARM rules change by loan program

Caps, indexes and qualifying rules come from the program behind the loan, not from the label “ARM.”

Conventional ARMs

Fannie Mae requires each ARM plan to carry both lifetime and per-adjustment rate change limits and to use the 30-day average SOFR index. The fully indexed rate is the index plus the margin, rounded to the nearest one-eighth percent, and on 3- and 5-year ARMs the gap between the initial note rate and the fully indexed rate at origination may not exceed 3 percentage points (Selling Guide B2-1.4-02, December 2025).

Qualifying is where the fixed period really matters. An ARM fixed for three years or less is qualified at the maximum rate that could apply during the first five years after the first payment. A 5-year ARM is qualified at the greater of the fully indexed rate or the note rate plus the first rate change cap. Beyond five years, qualifying uses no less than the note rate with an exception requiring the greater of the two on higher-priced mortgage loans (Selling Guide B3-6-04).

FHA ARMs

FHA offers a standard one-year ARM plus hybrids with 3-, 5-, 7- and 10-year introductory periods, and HUD sets the caps by product rather than leaving them to lenders.² One- and three-year FHA ARMs may rise by one percentage point annually and five over the life of the loan. Five-year FHA ARMs use either that 1%/5% structure or a 2%/6% structure. Seven- and ten-year FHA ARMs may rise by two points annually and six over the life of the loan. Our guide to government-backed loans compares FHA, VA and USDA financing.

VA ARMs

VA’s rule is the tightest of the agency programs: no single adjustment may change the rate by more than one percentage point in either direction, and adjustments across the entire term may not move it more than five points in either direction from the initial contract rate, tied to the weekly average yield on one-year (52-week) Treasury bills adjusted to a constant maturity (38 CFR 36.4312(d)).³ VA hybrid ARM products are authorized separately, so read the caps on your own note.

Jumbo ARMs

“Jumbo” isn’t a dollar amount, it’s any loan above the applicable conforming loan limit for that county. FHFA set the 2026 baseline one-unit limit at $832,750, with the high-cost-area ceiling at 150% of the baseline, or $1,249,125. Above the limit where you’re buying, terms come from the investor or the lender holding the loan rather than an agency guide, so caps and indexes vary. Compare AIR tables, not just rates.

Because Align Lending is a broker, we can price a conventional ARM, an FHA hybrid ARM and a 30-year fixed loan against each other on the same file.

Which one fits your timeline?

The honest test is one question: how many years will this loan be yours? Match that against the ARM’s fixed period and the decision makes itself.

Under 5 years, with real evidence: A 5/6m or 7/6 ARM’s lower introductory rate is money you keep, with no exposure to an adjustment you never reach. “Real evidence” means a military transfer window or a program with an end date, not a feeling that you’ll move.
5 to 10 years: The gray zone, and the fix is to buy more fixed period rather than more optimism. A 10/6 ARM covers a horizon a 5/1 doesn’t. If the gap between the 10-year ARM and the 30-year fixed is thin, take the fixed loan.
More than 10 years, or a fixed income: Take the fixed rate. Retirees, single-income households and anyone whose budget has no room for a several-hundred-dollar increase are the clearest cases there are.
You genuinely can’t answer: Default to fixed. Certainty is the cheaper mistake. Overpaying slightly on a rate you can refinance beats a payment you can’t carry.

One trap worth naming: “I’ll just refinance before it adjusts” depends on conditions years out. The CFPB says it directly. You might not qualify if your home’s value falls or a job loss or medical event damages your finances.

Keep the rate structure separate from the down payment question, too. Both a 3%-down and a 20%-down loan can be written fixed or adjustable; our overview of low-down-payment mortgages covers that side, and our post on the pros and cons of adjustable-rate mortgages argues the ARM case both ways.

FAQ: Fixed vs. adjustable-rate mortgages

Here are answers to common questions about fixed-rate and adjustable-rate mortgages.

What does the 5/1 in a 5/1 ARM mean?

The first number is how many years the introductory rate stays fixed, five. The second is how often the rate can adjust after that, once per year. A 7/6 ARM is fixed for seven years, then adjusts every six months. The name tells you nothing about the caps or the index, so ask for those separately. See our tips for shopping an adjustable-rate mortgage.

Is an ARM riskier than a fixed-rate mortgage?

It carries payment risk a fixed-rate loan does not, but the risk is bounded. Caps limit how much the rate can rise at the first adjustment, at each one after, and across the loan’s life. Ask your lender to run the payment at the lifetime cap. If you could still afford it, the risk is manageable; if not, take the fixed rate. Our ARM pros and cons covers both sides.

Can I switch from an ARM to a fixed-rate mortgage?

Yes, by refinancing into a new fixed-rate loan, which means new closing costs and a new underwriting approval. Some ARMs include a conversion clause, but most do not, and any conversion formula and fee come from your loan documents. Plan well before your first adjustment. Qualifying depends on your income, credit and home value then. Start with our fixed-rate mortgage options.

When does an ARM actually save money?

When your ownership horizon is shorter than the fixed period. If you expect to sell or refinance within five to seven years, a 7/6 ARM’s lower start rate can save thousands with no exposure to an adjustment. The math turns against you when plans change and you still hold the loan at reset. Our guide to choosing the right mortgage type works through it, and the CFPB’s loan comparison tools help you line up offers.

The bottom line on fixed vs. adjustable-rate mortgages

A fixed-rate mortgage holds one rate for the entire term, so the principal-and-interest payment is identical in month 1 and month 360. An ARM trades that certainty for a lower introductory rate over a set period, commonly 5, 7 or 10 years, then resets to an index plus a fixed margin, within caps written into your note. Those caps turn the worst case into a number rather than a fear: a $300,000 loan starting at 6% under a 2/2/5 structure tops out at 11% and roughly $2,718 a month. If you could carry that payment, the ARM is a real option. If not, the fixed rate is your answer.

If you’re ready to see both structures priced on your actual file, talk to Align Lending, we’ll shop your scenario across our lender network and put the fixed-rate and ARM numbers side by side, including the payment at the ARM’s ceiling. Call 248-506-5727 or start online today.

Footnotes:

1. Example figures in this article are hypothetical and for educational purposes only; they do not constitute an advertisement of credit terms or a rate quote under federal or state lending laws. The 3% / 8% / $910.66 / $1,467 figures come from the sample Loan Estimate published in the CFPB’s Consumer Handbook on Adjustable-Rate Mortgages and illustrate that sample loan, not current market pricing. The $300,000 cap-ladder example assumes a 30-year term, a 6% start rate, a 2/2/5 cap structure and the maximum permitted increase at every adjustment; actual results depend on the index, your margin, your note’s caps and market conditions. Your rate and terms will depend on your application. Return to text.

2. Align Lending is not acting on behalf of or at the direction of FHA or HUD. FHA adjustable-rate mortgage products, eligible indexes and interest rate caps are set by HUD in 24 CFR 203.49 and Single Family Housing Policy Handbook 4000.1 and are subject to change. Return to text.

3. Align Lending works with VA-approved lenders and is not endorsed or sponsored by the Dept. of Veterans Affairs or any government agency. VA adjustable-rate mortgage terms are set by VA regulation and are subject to change; confirm the caps and index on your own note. Return to text.

Figures current as of August 2026; verify current limits with the linked source before relying on them.

Sources: interest rate equals index plus margin; the 5/1 and 5/6m naming convention; the sample Adjustable Interest Rate table showing a 3% initial rate, a 2.5% margin, a 2.5%/8% minimum and maximum rate, a 2% first-change limit and a 2% subsequent-change limit; the $216,000 sample loan with a $910.66 principal-and-interest payment rising to a maximum of $1,467 in year 8; the teaser-rate example in which a 3% start rate rises to a 4.5% fully indexed rate (2% index plus 2.5% margin) even if the index does not move; the servicer notice arriving seven to eight months in advance; the conversion-option discussion; and the warning not to count on refinancing before the rate and payment increase, Consumer Financial Protection Bureau, Consumer Handbook on Adjustable-Rate Mortgages (CHARM booklet). CHARM booklet and ARM program disclosure delivered when an application form is provided or before payment of a non-refundable fee, 12 CFR 1026.19(b). First-adjustment notice at least 210 but no more than 240 days before the first payment at the adjusted level is due; subsequent-adjustment notices at least 60 but no more than 120 days, 12 CFR 1026.20(c) and (d). Requirement that each ARM plan offer lifetime and per-adjustment interest rate change limitations, that lifetime limitations apply to increases only, that the rate never decrease below the margin, that the plan be tied to the 30-day average SOFR index published by the Federal Reserve Bank of New York, the fully indexed rate defined as index plus margin rounded to the nearest one-eighth percent, and the 3% limit between the initial note rate and the fully indexed rate on 3- and 5-year ARMs, Fannie Mae Selling Guide B2-1.4-02 (December 10, 2025). ARM qualifying rates by initial fixed-rate period, including the higher-priced mortgage loan exception, Fannie Mae Selling Guide B3-6-04. FHA standard one-year ARM and 3-, 5-, 7- and 10-year hybrid ARMs, with caps of one percentage point annually and five over the life of the loan for 1- and 3-year ARMs, either 1%/5% or 2%/6% for 5-year ARMs, and two percentage points annually and six over the life of the loan for 7- and 10-year ARMs, U.S. Department of Housing and Urban Development, FHA Adjustable Rate Mortgage program; eligible FHA indexes of the Constant Maturity Treasury index and the 30-day average SOFR, 24 CFR 203.49. VA adjustable-rate mortgage limits of one percentage point per adjustment and five percentage points over the entire term, in either direction, indexed to the weekly average yield on one year (52 weeks) Treasury bills adjusted to a constant maturity, 38 CFR 36.4312(d)(1) and (d)(4)(i). Cessation of all U.S. dollar LIBOR panel settings after June 30, 2023 and the SOFR-based replacement rates, Board of Governors of the Federal Reserve System (Regulation ZZ, implementing the Adjustable Interest Rate (LIBOR) Act) and Consumer Financial Protection Bureau LIBOR transition guidance. 2026 baseline conforming loan limit value of $832,750 for one-unit properties and the high-cost-area ceiling of $1,249,125 (150% of the baseline), Federal Housing Finance Agency, Conforming Loan Limit Values for 2026. Weekly 30-year fixed-rate average published since April 1971 and the 18.63% high in 1981, Freddie Mac Primary Mortgage Market Survey.

This article is for informational purposes only and is not intended to provide legal, financial, or tax advice. Loan limits, program rules, indexes and cap structures change, and the caps that govern your loan are the ones stated in your own note and Loan Estimate; confirm your figures with your lender and consult a qualified professional about your situation. Figures shown are illustrative, are not a rate quote or an offer of credit, and are subject to change. Align Lending is an independent Michigan mortgage broker, NMLS #2041154.