FHA Adjustable-Rate Mortgages
October 21, 2025
While some homebuyers using an FHA loan opt for the stability of a fixed-rate mortgage, the FHA also offers another option: the Adjustable-Rate Mortgage (ARM).
An ARM can provide upfront savings, but it comes with a different set of rules and risks centered on how its interest rate can change over time. We examine the key components of FHA ARMs, from how the rates are calculated to the crucial protections that keep payments in check.
Are You Right for an FHA ARM?
An ARM can be an option for those who do not plan to live in the home for a long time. Someone expecting to relocate for work within a few years could sell the home before the first rate adjustment. An ARM can also be suitable for those who confidently expect their income to rise, allowing them to comfortably handle potential payment increases in the future.
The borrower trades long-term predictability for short-term affordability. You receive the immediate benefit of a lower initial payment but accept the risk that your payments could rise in the future. The built-in caps mitigate this risk, but they do not eliminate it.
Primary Benefit of an FHA Adjustable-Rate Mortgage (ARM)
The main advantage is its initial interest rate, which is typically lower than the rate for a standard 30-year fixed-rate loan. This lower rate can reduce monthly payments for the first several years of the mortgage, making homeownership more affordable upfront.
What the Numbers in an ARM Mean
The first number indicates the length of the initial, fixed-rate period in years. For a 5/1 ARM, the interest rate is fixed for the first five years. The second number shows how often the rate can be adjusted after the initial period ends. The "1" means the rate is subject to adjustment once per year.
How the Interest Rate is Calculated After the Initial Period Ends
The rate is determined by a simple formula: Index + Margin = Your Interest Rate. This is not an arbitrary decision by the lender but is tied to a public economic indicator.
The "Index" in an FHA ARM
The index is a benchmark that reflects general interest rate trends. For most FHA ARMs, the index is the weekly average on U.S. Treasury securities, which are adjusted to a constant maturity of one year. This is also known as the 1-Year Constant Maturity Treasury (CMT). Your rate will move up or down based on the movement of this index.
The "Margin" in an FHA ARM
The margin is a fixed number of percentage points that the lender adds to the index. It represents the lender's profit. The margin is set when the loan is originated and does not change for the life of the loan.
FHA ARM Caps
Caps are safety features that protect the borrower from extreme increases in their interest rate and monthly payment. The FHA mandates a system of caps on all its ARMs to limit how much the rate can change over time.
Initial Adjustment Cap: This limits the interest rate increase at the very first adjustment after the fixed-rate period ends. This is usually a 1 or 2 percentage point limit.
Periodic Adjustment Cap: This limits how much the rate can increase in any single year after the first adjustment. This is also typically a 1 or 2 percentage point limit.
Lifetime Cap: This sets an absolute ceiling on how high the interest rate can ever go. For FHA loans, this is usually 5 or 6 percentage points above the initial starting rate.
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