Definition
An Adjustable Rate Mortgage (ARM) is a mortgage loan where the interest rate is fixed for an initial period and then resets periodically based on a reference index plus a lender margin. After the first reset, the borrower’s payment may increase or decrease as market interest rates change.
How It Works
Most ARMs are described using a format like 5/1 or 7/6:
- 5/1 ARM: Fixed rate for 5 years, then rate adjusts once per year.
- 7/6 ARM: Fixed rate for 7 years, then rate adjusts every 6 months.
Key ARM components
- Index: A market rate used as the base (varies by lender and product).
- Margin: A fixed markup added to the index to determine the new rate.
- Reset frequency: How often the interest rate can change after the fixed period.
- Caps: Limits on how much the rate can increase (or decrease) at reset.
Rate Caps (Why They Matter)
ARM caps define the worst-case payment shock. Caps are commonly expressed as initial / periodic / lifetime caps (for example, 2/2/5):
- Initial cap: Maximum change at the first reset (e.g., 2%).
- Periodic cap: Maximum change at each subsequent reset (e.g., 2%).
- Lifetime cap: Maximum total increase over the life of the loan (e.g., 5%).
Why It Matters for Investors
ARMs can offer lower initial rates than fixed-rate loans, which may increase early cash flow. The tradeoff is interest-rate risk: if rates rise, debt service rises, pressuring DSCR and cash flow.
Investor Uses
- Bridge-to-agency strategy: Use a shorter-term ARM/bridge loan during renovation, then refinance into fixed-rate debt at stabilization.
- Short hold periods: Investors expecting to sell or refinance before the reset may prefer ARMs.
- Rate views and hedging: Sophisticated borrowers may combine ARMs with caps/swaps to manage risk.
Example
A borrower takes a 5/1 ARM with an initial rate of 6.00% for five years. The loan resets annually based on Index + Margin. If the index rises and the new calculated rate is 8.25%, but the first reset cap is 2%, then the rate at the first reset becomes 8.00% (not 8.25%).
Common Pitfalls
- Underwriting to the teaser rate: Use stressed rates (or max cap rate) when modeling durability.
- Ignoring cap structure: Periodic and lifetime caps determine real downside.
- Mismatch with business plan: If stabilization takes longer, you may reset into higher debt service before refinance.
- Not budgeting for hedges: Interest rate caps and swaps have real costs that reduce yield.