Fixed-rate and adjustable-rate mortgages: How loan structure works

Your loan’s structure, fixed or adjustable, 15-year or 30-year, decides how much of your payment can change and how much total interest you’ll pay. A 30-year fixed locks the same principal-and-interest payment for all 360 payments. A 5/6 ARM holds one rate for five years, then adjusts every six months inside caps such as 2/1/5, so the rate can move, but only so far and so fast.

Shortening a 30-year term to 15 typically raises the payment roughly 30% – 40% while cutting total interest by more than half. Learn more about fixed-rate and adjustable-rate mortgages, including how ARM caps work, what happens at a reset, and how loan term changes your total interest.

Key takeaways:

• Fixed = certainty: A fixed-rate mortgage keeps the same principal-and-interest payment for the entire term, 360 payments on a 30-year loan, even though your escrowed taxes and insurance still change.
• ARM = a bounded bet: A 5/6 ARM holds its rate for 5 years, then adjusts every 6 months based on an index plus a fixed margin, limited by caps such as 2/1/5, a maximum 2% first adjustment, 1% per adjustment after, and 5% over the life of the loan.
• Term is the bigger lever than most buyers realize: Moving from 30 years to 15 typically raises the monthly payment roughly 30% – 40% but cuts total interest by more than half, because 15-year rates usually run 0.50% – 0.75% lower and the balance amortizes far faster.

What is a fixed-rate mortgage?

A fixed-rate mortgage is a loan whose interest rate is set at closing and never changes, so the principal-and-interest portion of your payment is identical for all 360 payments on a 30-year term. Underneath, the split shifts: early payments lean toward interest, later ones toward principal, as the CFPB explains in how paying down a mortgage works. One caveat: escrowed taxes and insurance are re-analyzed annually, so your total payment can still move. “Fixed” describes the loan, not the tax bill.

• Terms beyond 30 and 15: Wholesale lenders also write 10-, 20- and 25-year fixed loans. The 20-year prices below a 30-year and lands the payment between them, our guide to fixed-rate mortgage options compares them all.
• The trade-off: Certainty for decades makes every other money decision easier to plan, but you pay for it in rate, and if you sell in four years you bought insurance you never used, one of the drawbacks of a fixed rate people forget.
• A shorter term is not the same as prepaying: A 15-year note obligates you to the higher payment; prepaying a 30-year keeps the right to stop in a hard month, at the cost of the rate discount.

Structure sits on top of program, not beside it. Every family of loan in our loan types and programs hub comes in both versions, conventional loans, FHA loans³ and VA loans² are all written as fixed-rate or adjustable-rate notes. Because Align is a broker rather than a lender, we can price the same program as a 30-year fixed at one wholesale lender and a 5/6 ARM at another, side by side, instead of showing you one bank’s version of both.

What is an adjustable-rate mortgage?

An adjustable-rate mortgage holds one rate for an introductory period, commonly 5, 7 or 10 years, then recalculates it on a fixed schedule for the rest of the term. It doesn’t float with the market; it moves on set dates, by a formula, inside a ceiling in your note. Three pieces of machinery decide what it becomes.

• Index: The public benchmark your rate follows. Fannie Mae and Freddie Mac ARMs use a 30-day average of the Secured Overnight Financing Rate (SOFR), which replaced LIBOR after U.S. dollar LIBOR panels ended in mid-2023.
• Margin: A fixed number added to the index at every adjustment, set at closing and unchanged for the life of the loan, the most important figure to compare between lenders. Fannie Mae and Freddie Mac both cap the margins allowed on the SOFR-indexed ARMs they buy, but within that band the margin is the lender’s choice, so it varies from quote to quote. Ask for it in writing.
• Caps: The limits on how far the rate can move, read as initial / periodic / lifetime. Under 2/1/5 the first adjustment can’t exceed 2 percentage points, each later one 1 point, and the rate can never exceed 5 points above the start.

The names confuse buyers more than anything else in lending, so here’s the decoder: in a 5/6 ARM, the 5 is years the rate stays fixed and the 6 is months between adjustments afterward. Same for a 7/6 and a 10/6. Different units in each digit, which is why it trips people.

The useful way to hold it: an ARM is a fixed-rate loan with an expiration date on the rate, not on the loan. Weigh the adjustable-rate mortgage pros and cons against your real timeline, and read the pros and cons of ARMs in detail before the opening payment settles it.

Fixed vs. ARM: Which one makes sense for you?

An ARM makes sense when you’re confident you’ll sell or refinance before the fixed period ends. The initial discount over a 30-year fixed is usually a fraction of a percentage point, and that discount is the entire size of the bet, your upside capped by it, your downside by the lifetime cap. Check the current spread in Freddie Mac’s Primary Mortgage Market Survey.

A fixed rate makes sense if:

• You want one number to plan around: Principal and interest is the same in year 1 and year 30.
• You can’t say when you’ll move: Most people who plan on five years stay longer; a plan is not a closing date.
• The lifetime-cap payment would strain you: If the worst case doesn’t fit the budget, no discount is big enough.

An ARM makes sense if:

• Your exit is scheduled, not hoped for: A military relocation, a fellowship that ends, a build-and-sell plan with a date on it.
• You could carry the capped payment anyway: Then an adjustment is an annoyance, not an emergency.
• The discount is big on your loan size: A quarter point moves real money on a $600,000 loan and very little on a $150,000 one.

Arguing against our own interest: search “ARM vs. fixed-rate mortgage” and you’ll find enthusiasm for the opening payment, but for a buyer staying 15 years or more that discount rarely justifies the exposure. Read the benefits and drawbacks of fixed-rate mortgages next to adjustable-rate mortgages: pros and cons. If you can’t name the year you’ll leave, take the fixed rate.

Loan term: 15-year vs. 30-year (and the options in between)

Term changes your total cost more than buyers expect, and our 15-year vs. 30-year mortgage comparison runs the full math. Here it is on a Michigan number: a $280,000 loan on a Waterford home at an illustrative 6.500% for 30 years and 5.875% for 15, sample figures, not a quote.¹

• 30-year fixed: About $1,770 a month in principal and interest, and roughly $357,100 of total interest.
• 15-year fixed: About $2,344 a month, and roughly $141,900 of total interest.
• The trade: $574 more each month buys back about $215,200, a payment 32% higher for an interest bill 60% smaller.

Two forces produce that gap: the balance amortizes twice as fast, and the rate runs lower because the lender’s money is at risk half as long. The flexibility argument still deserves a hearing: pay a 30-year on a 15-year schedule and you capture most of the savings while keeping the right to fall back to the smaller required payment in a hard year. One consequence buyers rarely see coming: the higher 15-year payment raises your debt-to-income ratio, which shrinks the purchase price you qualify for.

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.¹

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.

What happens when an ARM resets

You get roughly seven months of warning. Under federal Truth in Lending rules, your servicer must deliver the initial rate-adjustment notice at least 210 but no more than 240 days before the first adjusted payment is due, and later adjustments carry their own notice at least 60 days ahead.

The mechanics are arithmetic. On the change date the servicer takes the current index, adds your fixed margin, rounds to the nearest one-eighth of a percentage point, and applies the caps. Then it recalculates the payment to fully repay the balance over the remaining term, a reset in year six re-amortizes over 24 years, not 30. Our guide to adjustable-rate mortgage resets walks a change date step by step.

If rates are higher at your reset

Your rate rises only as far as the initial cap allows, 2 percentage points under a typical 2/1/5, no matter how far the index moved. Later moves are limited to the periodic cap, and the lifetime cap is the true ceiling. Price that capped payment before you close, not after the notice arrives.

If rates are lower at your reset

Your rate can fall, but not without a floor. Most ARM notes set a minimum rate; the standard agency note puts those limits in Section 4(D), read it before assuming a falling market helps you.

The exit math: divide refinance closing costs by the monthly savings for your break-even in months. Pay $4,800 to save $200 a month and you break even in 24 months.

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.³ 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)).² 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.

Getting the most out of whichever structure you choose

If you’re taking a fixed rate

• Shop the same term on the same day: Pricing moves daily, so Tuesday and Friday quotes aren’t comparable.
• Weigh discount points against your timeline: Points only pay off if you hold past the break-even month.
• Read the gap between rate and APR: A wide spread signals heavy fees behind a low headline rate, the CFPB explains the difference between rate and APR, and our fixed-rate mortgage tips cover the rest.

If you’re taking an ARM

• Compare margins, not teaser rates: The intro rate expires; the margin never does. Two ARMs with the same starting rate can diverge sharply at the first adjustment.
• Confirm the caps in writing: Get initial, periodic and lifetime caps on paper before you lock, and price the payment at that cap.
• Calendar your change date the week you close: Set the reminder six months ahead so the refinance decision is planned, our adjustable-rate mortgage tips cover the rest.

FAQ: Fixed-rate and adjustable-rate mortgages

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

Can I refinance out of an ARM before it adjusts?

Yes, and most ARM borrowers who stay in their homes plan on exactly that. There’s no penalty for refinancing an ARM on nearly all conforming programs, though you’ll pay closing costs again, so the move only makes sense if you’ll stay long enough to clear the break-even point. Start looking about six months before your first adjustment date, since a refinance takes 30 – 45 days and you want options rather than a deadline.

What happens to my ARM if rates fall?

Your rate can drop, but only down to the loan’s floor. At each adjustment the servicer recalculates your rate as the index plus your fixed margin, subject to the periodic cap in both directions, and most notes include a rate floor, often equal to the margin itself, below which the rate cannot go no matter how far the index falls. Check your note for the floor before you assume a falling market will help you.

Does a 15-year mortgage actually get a lower rate?

Usually, yes. Typically 0.50% – 0.75% below the 30-year rate on the same day for the same borrower, because the lender’s money is at risk for half as long. That rate gap is why the total interest savings on a 15-year loan are so much larger than the shorter term alone would suggest. The trade-off is a required payment roughly 30% – 40% higher at current rates, which also reduces the purchase price you can qualify for.

What’s the difference between a 5/1 ARM and a 5/6 ARM?

Only the adjustment frequency after the fixed period. Both hold their rate for the first five years; a 5/1 then adjusts once a year, while a 5/6 adjusts every six months. Most ARMs written today are 5/6, 7/6, or 10/6 because they’re tied to SOFR, which replaced LIBOR as the standard index. More frequent adjustments mean smaller individual moves, since the periodic cap applies to each one.

The bottom line: Fixed buys certainty, an ARM buys a discount with an expiration date

A 30-year fixed sets your principal-and-interest payment once and holds it for all 360 payments. A 5/6 ARM holds its rate five years, then adjusts every six months inside caps such as 2/1/5, a bounded bet: a small opening discount against a lifetime-cap downside. Term is the larger lever either way: 15-year rates typically run 0.50% – 0.75% below 30-year rates, cutting total interest by more than half while raising the payment 30% – 40%.

If you’re ready to see all three priced on your real numbers, talk to Align Lending, we’ll quote fixed and adjustable options across our lender network side by side. Call 248-506-5727 or get started online today.

Footnotes:

1. Example figures 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. Your rate and terms will depend on your application and market conditions. Return to text
2. Align Lending works with VA-approved lenders and is not endorsed or sponsored by the Department of Veterans Affairs or any government agency. Return to text
3. Align Lending is not acting on behalf of or at the direction of FHA or HUD. Return to text

This article is for informational purposes only and is not intended to provide legal, financial, or tax advice. Consult a qualified professional about your situation. Rates, payment figures, margins, and cap structures shown are illustrative, are not a rate quote or an offer of credit, and are subject to lender overlays and change. Align Lending works with FHA- and VA-approved lenders and is not acting on behalf of, endorsed by, or sponsored by FHA, HUD, the Department of Veterans Affairs, or USDA.