Glossary term
Initial Interest Rate (ARM)
An ARM initial interest rate is the starting rate charged during the first fixed or introductory period of an adjustable-rate mortgage.
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What Is an ARM Initial Interest Rate?
An ARM initial interest rate is the starting interest rate charged during the first fixed or introductory period of an adjustable-rate mortgage. It is the rate borrowers often see advertised most prominently, but it may not be the rate that applies for the full loan term.
The initial rate can be lower than the rate on a comparable fixed-rate mortgage, which is part of the appeal of an ARM. The tradeoff is that the rate can adjust later based on the loan's index, margin, and caps.
Key Takeaways
- The initial interest rate is the ARM's starting rate.
- It may last for a fixed introductory period such as three, five, seven, or ten years.
- The rate can change after the initial period according to the ARM terms.
- Borrowers should compare the initial payment with possible future payments, not just the starting rate.
How the Initial Rate Works
During the initial period, the ARM rate usually stays fixed. For a 7/1 ARM, for example, the starting rate generally applies for seven years before the loan begins adjusting annually. For a 5/6 ARM, the starting rate generally applies for five years before adjustments every six months.
After the initial period ends, the new rate is typically calculated by adding the loan's margin to its index, subject to caps. If market rates have risen, the borrower's payment can rise. If market rates have fallen, the rate may fall, depending on the loan terms and any floors.
Initial Rate Versus Later Rate
Feature | Initial period | After adjustment begins |
|---|---|---|
Rate source | Set by the loan terms at closing | Index plus margin, subject to caps |
Payment predictability | More predictable | Can change at reset dates |
Main borrower risk | Focusing only on the low starting payment | Payment shock if rates rise |
Review point | Length of introductory period | Caps, index, margin, and maximum payment |
What Borrowers Should Model
The initial interest rate is useful, but it can be misleading if viewed alone. Borrowers should ask what the payment would be after the first adjustment, at the maximum first-adjustment cap, and at the lifetime cap.
A low initial rate can make a loan affordable at closing while still creating future payment risk. The safer comparison is the full ARM structure against the borrower's expected time in the home, refinance risk, income stability, and tolerance for payment changes.
The Bottom Line
An ARM initial interest rate is the starting rate before later adjustments begin. It can lower early payments, but borrowers should evaluate the future reset formula and maximum payment before relying on the introductory rate.