Adjustable-Rate Mortgages (ARMs): How They Work, Pros, and Cons

Understand how your mortgage interest rate can change over time and if an ARM is right for your financial situation.

By Garret Merkley · Explainer · Jun 6, 2026

Branched from Understanding Interest Rate Indexes and Margins on Variable Loans

Quick take

ARMs offer a lower initial interest rate for a set period, then adjust based on market conditions.
Your payment can change significantly after the fixed period, influenced by an index, margin, and rate caps.
They suit borrowers planning to move or refinance soon, or those expecting future income growth.
Carefully weigh the potential for increased payments against initial savings and your financial risk tolerance.

An Adjustable-Rate Mortgage (ARM) is a type of home loan where the interest rate can change periodically after an initial fixed period. Unlike a fixed-rate mortgage, where the interest rate remains the same for the entire loan term, an ARM’s rate fluctuates according to market conditions, which means your monthly payment can go up or down.

How Adjustable-Rate Mortgages Work

ARMs typically begin with a fixed interest rate for a set number of years, usually 3, 5, 7, or 10 years. During this initial period, your monthly principal and interest payments remain stable. Once this fixed period ends, the interest rate begins to adjust at regular intervals, often annually or semi-annually. Each adjustment period brings a new interest rate, which then determines your new monthly payment until the next adjustment.

The Key Components: Index, Margin, and Caps

The mechanics of an ARM’s rate adjustments rely on three main components: the index, the margin, and rate caps. The index is a publicly available economic indicator, like the Secured Overnight Financing Rate (SOFR) or the Constant Maturity Treasury (CMT). Your ARM’s interest rate will move in tandem with this index. The margin is a fixed percentage point amount that the lender adds to the index to calculate your actual interest rate. This margin is set when you take out the loan and does not change.

Rate caps are protective limits on how much your interest rate can change. An initial cap limits the first adjustment after the fixed period ends. Periodic caps restrict how much the rate can change in any subsequent adjustment period. Finally, a lifetime cap sets the maximum interest rate your loan can ever reach over its entire term, providing a ceiling on your potential payments.

Understanding ARM Notation

ARMs are often described with a fraction, like '5/1 ARM' or '7/6 ARM'.
The first number (e.g., '5') indicates the number of years the initial fixed interest rate applies.
The second number (e.g., '1') indicates how often the rate adjusts after the fixed period (e.g., every 1 year for a 5/1 ARM, or every 6 months for a 7/6 ARM).

ARMs can be beneficial if you anticipate moving or refinancing before the initial fixed period expires, allowing you to take advantage of a lower introductory rate without facing potential increases. They are also attractive to borrowers who expect their income to rise significantly in the future, making higher payments more manageable down the line. The primary advantage is typically a lower initial interest rate and thus a lower monthly payment compared to a fixed-rate mortgage. However, the main drawback is payment uncertainty. If market interest rates rise significantly, your monthly payments could increase substantially, potentially straining your budget. It’s crucial to assess your financial stability and comfort with potential payment fluctuations before choosing an ARM.

What's the main difference between an ARM and a fixed-rate mortgage?

The main difference is how the interest rate behaves. A fixed-rate mortgage's interest rate stays the same for the entire loan term, providing predictable payments. An ARM's interest rate is fixed for an initial period, then adjusts periodically based on market conditions, meaning your payments can change.

How do I know what my ARM rate will be after the fixed period?

Your new rate is calculated by adding the fixed margin to the current value of the chosen index (e.g., SOFR + 2.5%). This new rate is then subject to any initial or periodic caps, which limit how much it can change from the previous rate.

Are ARMs always riskier than fixed-rate mortgages?

Not necessarily, but they carry more interest rate risk. If interest rates rise, your payments could increase. However, if rates fall, your payments could decrease. The risk level depends on your financial situation, your plans for the home, and your tolerance for payment fluctuations.

Can I refinance an Adjustable-Rate Mortgage?

Yes, you can typically refinance an ARM. Many borrowers choose to refinance into a fixed-rate mortgage before their initial fixed period ends, especially if interest rates are favorable, to lock in a stable payment and avoid potential rate increases.