What Is an ARM?

An adjustable-rate mortgage has two phases:

1. Intro period (typically 3, 5, 7, or 10 years): Your rate is fixed — and usually lower than a comparable fixed-rate mortgage.
2. Adjustment period (remaining years): Your rate adjusts annually based on a market index, subject to caps.

A "5/1 ARM" means 5 years fixed, then adjusting every 1 year. A "7/6 ARM" means 7 years fixed, adjusting every 6 months.

The Rate Caps

ARMs have built-in guardrails:

Initial adjustment cap: How much the rate can change at the first adjustment (typically 2%)

Periodic cap: Maximum change at each subsequent adjustment (typically 2%)

Lifetime cap: The absolute maximum rate over the life of the loan (typically intro rate + 5%)

So a 5/1 ARM starting at 5.75% with a 5% lifetime cap can never exceed 10.75%, regardless of what happens to market rates.

When ARMs Win

If you sell or refinance before the intro period ends, the ARM saves you money — period. You got a lower rate for the years you held the loan and never faced the adjustment risk.

This makes ARMs a strong choice when:

You plan to move within 5-7 years (job relocation, growing family, downsizing)

You expect to refinance when rates drop

The rate spread is significant. If fixed rates are 6.75% and a 5/1 ARM offers 5.75%, that 1% spread on a $340,000 loan saves ~$220/month during the intro period — over $13,000 in the first 5 years.

When ARMs Lose

You stay past the intro period and rates have risen. Your payment increases, potentially significantly.

The rate spread is small. If the ARM only saves 0.25% over fixed, the risk isn't worth the minimal savings.

You can't absorb payment increases. Always check the worst case — your payment at the lifetime cap rate. If that number is unaffordable, the ARM is too risky.

The Break-Even Analysis

The key question is: at what point does the ARM's total cost catch up to the fixed-rate total cost? If you sell before that point, the ARM wins. If you stay past it, the fixed rate wins.

This break-even point depends on how aggressively rates adjust. In a moderate scenario, a 5/1 ARM with a 1% spread over fixed typically breaks even around year 8-10.

Model It

Load the ARM vs. Fixed template to see a pre-built comparison with realistic rate caps. The ARM vs. Fixed card shows the exact break-even point and total cost difference under the scenario you've selected.

Adjustable Rate Mortgages: Risk, Reward, and When They Win