Buying Tools
ARM Calculator
Calculate adjustable-rate mortgage payments during the fixed period, after the first adjustment, and worst-case scenario. No signup required.
ARM Loan Details
Lender margin + index = fully indexed rate
Current SOFR or other benchmark
Max rate change per adjustment
Max total rate increase over life
Monthly Payment (Fixed Period)
$0
Insights
How Adjustable-Rate Mortgages (ARMs) Work
An adjustable-rate mortgage (ARM) starts with an initial interest rate that remains fixed for a specified introductory period—commonly 3, 5, 7, or 10 years (referred to as a 3/1, 5/1, 7/1, or 10/1 ARM). During this initial phase, your monthly principal and interest payments remain stable and are typically lower than prevailing 30-year fixed mortgage rates, offering valuable short-term savings.
Once the fixed introductory period expires, your interest rate begins to periodically adjust (usually once per year) based on prevailing market benchmarks such as the Secured Overnight Financing Rate (SOFR). Your new adjusted interest rate is calculated by adding your lender's predetermined margin to the current index rate.
To protect borrowers from runaway interest rate spikes, ARMs feature strict rate caps. Adjustment caps limit how much your rate can increase during a single adjustment period, while lifetime caps establish an absolute ceiling on how high your interest rate can climb over the entire life of the loan.
ARM vs. Fixed-Rate: When Each Makes Sense
Deciding between an adjustable-rate mortgage and a traditional fixed-rate loan depends entirely on your financial horizon and risk tolerance:
- Choose an ARM if: You are confident you will sell the home, upgrade to a new property, or pay off the mortgage balance before the fixed introductory period ends (e.g., military families or corporate relocations).
- Choose a Fixed-Rate loan if: You intend to live in your forever home for decades, desire complete budget certainty, or when fixed mortgage rates are historically low.
Frequently asked questions
What is an adjustable-rate mortgage?
An adjustable-rate mortgage (ARM) is a home loan with an interest rate that is fixed for an initial period of time (typically 3, 5, 7, or 10 years) and then periodically adjusts up or down based on benchmark financial indices like SOFR.
How does an ARM adjustment work?
When your fixed-rate introductory period ends, your interest rate resets based on the current index rate plus your lender's margin. Subsequent adjustments happen periodically (usually annually). Rate caps limit how much your interest rate can increase per adjustment and over the lifetime of the loan.
What is the difference between margin and index?
The index is a benchmark financial interest rate (such as SOFR) that fluctuates with economic conditions. The margin is a fixed percentage set by your lender that remains constant throughout the life of your loan. Your fully indexed interest rate is simply the sum of the index rate plus the margin.
Are ARMs risky?
ARMs carry inherent payment shock risk if benchmark interest rates rise significantly after your fixed period expires. However, statutory rate caps protect borrowers from extreme spikes, and ARMs make financial sense for buyers who plan to sell or refinance before the introductory fixed period ends.
Should I choose an ARM or fixed-rate mortgage?
Choose a fixed-rate mortgage if you value long-term stability and plan to stay in your home for many years. Consider an ARM if you expect to relocate, upgrade your home, or pay off the mortgage within 5 to 7 years, as you will benefit from a lower initial interest rate.