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Loan Types

Adjustable-Rate Mortgages (ARMs) Explained: How They Work, Caps and When They Make Sense

An ARM is like a gym membership with a great intro price: lovely at first, but you had better read what happens after the promo. Here is how adjustable-rate mortgages really work.

By Keys & Coffee Editorial Team · Updated · 6 min read

Pen resting on a printed line chart showing values rising and falling
Quick answers

  • What it is: an adjustable-rate mortgage (ARM) has a fixed rate for an initial period, then the rate can move up or down on a set schedule.
  • The names: in a 5/6 ARM, the rate is fixed for 5 years, then adjusts every 6 months.
  • The formula: after the fixed period, your rate = an index (often SOFR) + a margin set in your loan, limited by caps.
  • Caps matter most: they limit how much the rate can rise at the first adjustment, each later adjustment and over the life of the loan.
  • Best fit: people who are fairly confident they will sell or refinance before the fixed period ends, and who could handle the payment if it rises.

An adjustable-rate mortgage is a bit like an introductory price on a streaming service. The starting price is tempting, and it might stay reasonable. But you want to know exactly how high the bill can go before you sign up.

Let’s break down how ARMs work, what all those slashes mean and how to tell whether one fits your plans.

How an ARM works

Every ARM has two phases:

  1. The fixed period. For the first few years, your rate does not change. This starting rate is often lower than a comparable 30-year fixed rate, though not always.
  2. The adjustable period. After that, the rate resets on a schedule based on a market index, plus a margin, within limits called caps.

Most ARMs still have a 30-year total term. The adjustments just change how much interest you pay along the way.

Decoding the numbers: 5/6, 7/6, 10/6

The first number is how many years the rate stays fixed. The second number is how often it adjusts after that. Today, many ARMs adjust every six months, which is why you see a “6.”

ARM type Fixed for Then adjusts
5/6 ARM 5 years Every 6 months
7/6 ARM 7 years Every 6 months
10/6 ARM 10 years Every 6 months
5/1 ARM (older style) 5 years Every 1 year

Index + margin = your new rate

When your ARM adjusts, the lender takes a published market index and adds a fixed margin. Many newer ARMs use SOFR, the Secured Overnight Financing Rate, which replaced the old LIBOR benchmark.

  • The index moves with the market. You do not control it.
  • The margin is set in your loan documents and stays the same for the life of the loan.

So if the index is 4% and your margin is 2.75%, the “fully indexed” rate would be 6.75%, subject to your caps. Those numbers are just for illustration.

Myth buster“My ARM rate can only go up.” Not true. If the index falls, your rate can fall too. Many loans have a “floor,” often the margin, so it will not drop below a certain level, but adjustments can go in either direction.

Rate caps: your seatbelt

Caps are the most important part of any ARM. According to the CFPB, there are three kinds:

Cap What it limits Commonly seen
Initial adjustment cap The first change after the fixed period 2 or 5 percentage points
Subsequent adjustment cap Each later change 1 or 2 percentage points
Lifetime cap Total increase over the starting rate 5 percentage points

Caps are often written as three numbers, like 2/1/5. That means the rate can rise up to 2 points at the first adjustment, up to 1 point at each later adjustment and no more than 5 points above the starting rate, ever.

Example

You borrow $300,000 with a 5/6 ARM at a hypothetical 5.75%, with 2/1/5 caps. A 30-year fixed loan is offered at a hypothetical 6.5%.

  • ARM payment (years 1 to 5): about $1,751 a month in principal and interest.
  • Fixed payment: about $1,896 a month.
  • That is about $145 a month less, or roughly $8,700 over the first five years.
  • After 60 payments, your balance is about $278,287. If the rate jumps the full 2 points to 7.75% at the first adjustment, the payment over the remaining 25 years becomes about $2,102.
  • If it eventually hits the 5-point lifetime cap (10.75%), the payment could reach about $2,677.

All rates are illustrative, not quotes. Taxes and insurance are extra.

Try your own scenarios in our mortgage calculator, and plan an exit with the refinance calculator.

ARM vs fixed-rate at a glance

ARM Fixed-rate
Starting rate Often lower Often higher
Payment after the intro period Can rise or fall within caps Principal and interest never change
Best for Shorter expected stays, flexible budgets Long stays, people who love predictability
Biggest risk Payment shock if rates climb Paying more up front if you move early

Neither one is “better” across the board. The right choice depends on how long you will keep the loan and how much payment wiggle room your budget really has. Be honest with yourself here: plans to move in five years have a funny way of turning into ten.

When an ARM can make sense

  • You expect to move within the fixed period. If you are pretty sure you will sell in five or six years, a 7/6 ARM’s fixed window may cover your whole stay.
  • Your income is likely to rise. A higher future payment is easier to handle with a bigger paycheck, though nothing is guaranteed.
  • The rate gap is meaningful. If the ARM’s starting rate is barely below a fixed rate, the risk may not be worth it.

When to think twice

  • You plan to stay in the home long term and value predictability.
  • Your budget could not absorb the worst-case payment allowed by the caps.
  • Your plan depends on refinancing later. Rates might not fall, and you have to qualify again when you refinance.

If you are torn between fixed options, our comparison of the 15-year vs 30-year mortgage is a good next read. And for context on where rates have been recently, see our October 2026 mortgage rates update.

Fun factThe CFPB publishes a free booklet called the Consumer Handbook on Adjustable-Rate Mortgages, nicknamed the “CHARM booklet.” Lenders are required to give it to you when you apply for an ARM. Yes, someone at a federal agency got to name it CHARM.

Questions to ask before you sign

  1. What index does this ARM use, and what is the margin?
  2. What are the initial, subsequent and lifetime caps?
  3. Is there a floor rate?
  4. What is the highest my payment could ever be, and when could it get there?
  5. Is there a prepayment penalty if I refinance or sell early?

Your Loan Estimate includes an Adjustable Interest Rate (AIR) table and projected payments that show much of this in black and white.

FAQ

What does 5/6 ARM mean?

The rate is fixed for the first 5 years, then can adjust every 6 months for the rest of the loan, within the caps.

Can I refinance out of an ARM?

Yes, many people refinance into a fixed rate before the first adjustment. You will need to qualify at that time, and it depends on rates then.

Is an ARM riskier than a fixed-rate mortgage?

It carries payment risk, because the rate can rise after the fixed period. Caps limit that risk, but they do not remove it.

Are ARM rates always lower than fixed rates?

Usually the starting rate is lower, but not always. Compare actual offers on the same day.

Do FHA and VA offer ARMs?

Yes, both programs allow certain adjustable-rate loans, with their own cap rules. Ask lenders which ARM options they offer.

Keys & Coffee is an independent education site and is not a lender. Examples are for illustration only. Sources: Consumer Financial Protection Bureau (ARM rate caps and the Consumer Handbook on Adjustable-Rate Mortgages), Federal Reserve Bank of New York (SOFR), Fannie Mae and Freddie Mac ARM guidelines.

Keys & Coffee Editorial Team

We turn lender-speak into plain English. We check our numbers against official sources like the CFPB, HUD, Fannie Mae and Freddie Mac, and we update guides when the rules change.

Keys & Coffee is an independent education site. We are not a lender or mortgage broker, we do not take loan applications or payments, and nothing here is financial advice. This site is not affiliated with Axia Home Loans, Axia Financial, LLC, or Planet Home Lending. Rates and rules change often — always confirm details with a licensed loan officer and check any lender on the NMLS Consumer Access site.

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