Adjustable-Rate Mortgages Explained: When an ARM Makes Sense and When It Doesn’t

Most buyers I work with default to a 30-year fixed loan, and for many of them it’s the right choice. But an adjustable-rate mortgage, or ARM, can be a smart tool in the right situation, especially in Northern Virginia, where many people move every few years for work, military orders or a growing family. The key is understanding exactly how the loan can change before you sign.

How an ARM works

An ARM has two phases. During the initial period, your rate is fixed, just like a fixed-rate loan. After that, the rate resets on a schedule based on two numbers: an index, which moves with the market (most new ARMs use SOFR, the Secured Overnight Financing Rate), and a margin, which is a fixed amount the lender adds and never changes.

The name tells you the structure. A 5/6 ARM is fixed for 5 years and then adjusts every 6 months. A 7/6 ARM is fixed for 7 years. A 10/6 ARM is fixed for 10 years.

Caps: the most important part of the fine print

Caps protect you from sudden jumps. They’re usually written as three numbers, such as 2/1/5.

Cap	What it limits	Example with 2/1/5 caps and a 6.25% start
Initial adjustment cap	The first change after the fixed period	Can rise to no more than 8.25%
Periodic cap	Each later change	No more than 1 point per adjustment
Lifetime cap	The highest the rate can ever go	Never above 11.25%

A worked example on a $600,000 loan

Let’s compare two 30-year loans for $600,000. Option one is a fixed rate at 7.00%. Option two is a 5/6 ARM starting at 6.25% with 2/1/5 caps. These rates are only for illustration.

	30-year fixed at 7.00%	5/6 ARM at 6.25%
Principal and interest, years 1 to 5	$3,992	$3,694
Monthly savings with the ARM	–	About $298
Total savings over 5 years	–	About $17,850
Loan balance after 5 years	About $564,800	About $560,000
Payment if the rate hits 8.25% in year 6	$3,992	About $4,416
Payment at the 11.25% lifetime cap	$3,992	About $5,590

If you sell or refinance within five years, the ARM saves you about $17,850 in payments and leaves you with a slightly lower balance. If you stay and rates rise to the cap, your payment could climb by roughly $1,600 a month compared with the fixed loan. Both outcomes are possible, which is why your timeline matters more than the starting rate.

Who an ARM can work well for

• Military families expecting orders in three to five years. See buying with PCS orders.
• Starter-home buyers who plan to move up when the family grows.
• Higher earners with strong savings who could handle the worst-case payment.
• Buyers who expect to refinance and accept the risk that rates may not fall.

What most people miss

• Refinancing is not guaranteed. You need equity, steady income and good credit at the time you want to refinance, and rates may not cooperate.
• Plans change. Many people expect to move in five years and end up staying ten. Pick a fixed period that covers your realistic timeline with a cushion.
• Qualifying rules differ. For some ARMs, lenders qualify you at a higher rate than the start rate, which can lower your maximum price.
• The margin is negotiable shopping data. Compare margins and caps between lenders, not just the start rate.

Frequently asked questions

Can I refinance out of an ARM before it adjusts?

Yes, as long as you qualify at the time. Learn how to judge the math in When Does Refinancing Make Sense?

Does my rate ever go down on an ARM?

It can. If the index falls, your rate can adjust lower at the next change, though many loans set a floor, often equal to the margin.

Are ARMs risky like before 2008?

Today’s ARMs require full income documentation and have clear caps, so they’re far more transparent. The risk is still real, so plan for the highest payment the caps allow. A good loan officer can show you both options side by side. Read How to Choose a Mortgage Lender.