Glossary term
Adjustment Period (ARM)
An ARM adjustment period is the interval at which an adjustable-rate mortgage's interest rate can change after the initial period.
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What Is an ARM Adjustment Period?
An ARM adjustment period is the interval at which an adjustable-rate mortgage's interest rate can change after the initial fixed-rate period ends. The adjustment period determines how often the loan can reset, such as every year, every six months, or at another interval specified in the loan documents.
The adjustment period is one of the core features that makes an ARM different from a fixed-rate mortgage. It affects payment uncertainty because a shorter adjustment period can expose the borrower to more frequent rate changes.
Key Takeaways
- The adjustment period tells you how often an ARM rate can reset after the initial period.
- Common intervals include annual and six-month adjustments.
- The new rate is usually based on an index plus a margin, subject to caps.
- Borrowers should review the adjustment period with the index, margin, and rate caps together.
How the Adjustment Period Works
An ARM usually starts with an initial period during which the interest rate is fixed. After that, the loan moves into its adjustment schedule. A 5/1 ARM, for example, generally has a fixed rate for five years and then adjusts once per year. A 5/6 ARM generally adjusts every six months after the initial five-year period.
At each adjustment date, the lender calculates the new rate using the ARM's index and margin, then applies any periodic or lifetime caps. The payment may change when the rate changes.
What to Check in the Loan Terms
Term | Why it matters |
|---|---|
Initial period | Shows how long the starting rate stays fixed |
Adjustment period | Shows how often the rate can change afterward |
Index | Provides the benchmark rate used for resets |
Margin | Is added to the index to set the adjusted rate |
Caps | Limit how much the rate can change at adjustment or over the loan life |
Payment Planning
The adjustment period matters because it affects how quickly market-rate changes can reach the borrower. A loan that adjusts every six months can move more often than one that adjusts annually. Even with caps, that can change the payment path over time.
Borrowers should model the payment at the initial rate, the first possible adjusted rate, and the maximum rate allowed by the loan. The adjustment period is only useful when read with the full ARM structure.
The Bottom Line
An ARM adjustment period is the reset interval for an adjustable-rate mortgage after the initial fixed period. It shapes how often the rate and payment can change, so it should be reviewed with the index, margin, caps, and worst-case payment.