ARM vs. Fixed-Rate Mortgages

A fixed rate never moves for the life of the loan. An adjustable-rate mortgage (ARM) starts lower, then can move — up or down — on a set schedule. The real question isn't which is "safer." It's how long you'll actually keep the loan.

How an ARM is built

ARMs are quoted like 7/6 or 5/6: the first number is how many years the intro rate is fixed; the second is how often it adjusts afterward (every 6 months). Once the intro period ends, your rate becomes an index (a public benchmark like SOFR) plus a fixed margin the lender set at closing. The margin never changes; the index does — so your rate rides the market from then on, within limits.

The caps that contain it

Every ARM carries rate caps: how much it can jump at the first adjustment, at each later adjustment, and over the loan's life. Read them as a worst case, not a footnote — a 5/1/5 cap structure means the rate could climb 5 percentage points over the life of the loan. If you can't comfortably afford the payment at the lifetime cap, the intro rate is a mirage.

When an ARM is rational

The ARM's lower intro rate is compensation for taking on that future risk. It pays off when your horizon is shorter than the fixed period: a known relocation, a starter home you'll sell in a few years, or a loan you're confident you'll pay off early. In those cases you capture the lower rate and are gone before the adjustment ever bites.

When fixed wins

If you'll hold the loan long-term, a fixed rate is certainty you can build a budget around — and "we'll just refinance later" quietly assumes rates will be lower and that you'll still qualify. Neither is guaranteed. Because fixed mortgage rates track the bond market (here's how), you can shop today's fixed rate against our neutral rate board and know exactly what you're locking in.

By L.W. Martin, Founder — 20 years in the mortgage business, including 15 running his own brokerage. About → · Updated August 2026.