ARM (Adjustable-Rate Mortgage)

Adjustable-rate mortgages trade rate certainty for a lower initial rate. The structure: a fixed-rate introductory period (typically 5, 7, or 10 years) followed by scheduled rate adjustments based on a stated index plus a fixed margin. Older loans adjusted once a year off the 1-year Treasury yield or LIBOR (the 5/1, 7/1 and 10/1 ARMs); since Fannie Mae and Freddie Mac stopped buying LIBOR ARMs at the end of 2020, new conforming ARMs adjust every six months off the 30-day average SOFR (Secured Overnight Financing Rate) — the 5/6, 7/6 and 10/6 ARMs — and legacy LIBOR loans were converted to SOFR when LIBOR ended in June 2023. Caps limit the first adjustment (typically 2 or 5 percentage points), each later adjustment (typically 1 point) and the lifetime increase over the start rate (typically 5 points). The result is a product where the borrower's payment is fixed for the introductory period and then exposed to rate risk on a defined schedule.

The economic case for ARMs is straightforward: in normal interest-rate environments, ARMs offer 0.25% to 1.00% lower initial rates than comparable fixed-rate mortgages. For a borrower planning to sell or refinance before the adjustment period — typically a 5/1 ARM holder planning to sell within 7 years, or a 7/1 ARM holder planning to sell within 9 years — the lower initial rate translates to meaningfully lower total interest over the holding period. The arithmetic on a $400,000 7/1 ARM at 5.75% versus a $400,000 30-year fixed at 6.50% saves roughly $3,000 per year in interest during the 7-year fixed period — $21,000 cumulatively if the borrower exits before adjustment.

The risk of ARMs is the reset. Borrowers who stay past the introductory period are exposed to whatever the rate environment looks like at adjustment. The cap structure — 2/1/5 on a typical 5/6 ARM, 5/1/5 on most 7/6 and 10/6 ARMs (first adjustment, later adjustments, lifetime) — limits the upside risk but does not eliminate it; a borrower in a 5/1 ARM that resets in a high-rate environment can see monthly payments rise materially. The borrower's protection is the ability to refinance before or during the reset, but the refinance is only available if the borrower's qualifying profile (income, credit, home equity) supports it at the time. A borrower whose income has fallen or whose home equity has dropped may find themselves "trapped" in an ARM at a higher rate than they would otherwise refinance into.

The strategic question with ARMs is not whether the lower initial rate is attractive — it always is — but whether the borrower's expected exit date is genuinely shorter than the introductory period, and whether the borrower can tolerate rate-reset risk if circumstances change. The honest math values the rate savings during the fixed period against the option value of fixed-rate certainty. For most borrowers with a long-term homeownership horizon, a 30-year fixed mortgage's structural simplicity is worth the slightly higher rate. For borrowers with a clear and confident exit plan well inside the introductory period, an ARM can be a meaningful savings opportunity. The mortgage hub's how-to-shop pillar covers the decision tree in detail.

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