Glossary term
3/1 ARM
A 3/1 ARM is an adjustable-rate mortgage with a fixed rate for three years and rate changes once per year after that.
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What Is a 3/1 ARM?
A 3/1 ARM is an adjustable-rate mortgage with a fixed interest rate for the first three years and rate adjustments once per year after that. The first number is the initial fixed period. The second number shows how often the rate can adjust after the fixed period ends.
The loan can offer a lower starting rate than a comparable fixed-rate mortgage, but that early payment certainty is temporary. After year three, the payment can change based on the loan's index, margin, caps, and remaining term.
Key Takeaways
- A 3/1 ARM has a three-year fixed-rate period.
- After the fixed period, the rate can adjust once each year.
- The adjusted rate is generally based on an index plus a margin.
- Rate caps limit how much the rate can change, but they do not eliminate payment risk.
- Borrowers should review the reset payment before relying on the starter rate.
How the Reset Schedule Works
During the first three years, the borrower pays the introductory fixed rate. At the first adjustment date, the lender recalculates the rate using the benchmark index and the margin stated in the loan documents. From there, the rate can adjust annually, subject to caps.
Because the fixed period is relatively short, a 3/1 ARM is more exposed to near-term rate changes than a 7/1 or 10/1 ARM. That can matter if the borrower expects to keep the home longer than three years or if refinancing is not available when the first reset arrives.
Features to Review Before Choosing One
Feature | What to check |
|---|---|
Initial fixed period | How long the starting payment is protected. |
Index | The benchmark that moves with market rates. |
Margin | The fixed amount added to the index. |
Adjustment caps | The maximum rate change at first reset, later resets, and over the loan's life. |
Refinance plan | Whether the plan still works if rates rise or home value falls. |
Where the Risk Sits
The risk is concentrated around the first reset. A borrower who qualifies comfortably at the starter payment may still struggle if the fully indexed rate is meaningfully higher. A 3/1 ARM can be especially risky when it is used to stretch affordability instead of matching a short expected holding period.
The loan may fit a borrower who has strong reserves, a credible plan to sell or refinance, and room for a higher payment. It is less forgiving for someone who needs the introductory payment to make the home affordable.
The Bottom Line
A 3/1 ARM is a mortgage with a three-year fixed-rate period followed by annual adjustments. Its appeal is the starting rate, but the real decision is whether the borrower can handle the payment after the fixed period ends.