Should I get an ARM or a 30-year fixed?
Run one comparison and the decision usually makes itself: the dollars the ARM saves during its fixed period versus the capped worst-case payment after it adjusts. An ARM fits when the fixed-period savings are meaningful AND you could absorb the worst case — start rate plus lifetime cap — without hardship; a fixed loan fits when you cannot, or when the ARM discount is too thin to pay for the risk (the spread between ARM and fixed pricing changes constantly, and sometimes disappears). The popular middle path — take the ARM and refinance before it adjusts — is a real strategy with real failure modes: rates, your credit, your income, and your home’s value all have to cooperate on a deadline.
Last reviewed 2026-08-24
The two numbers that decide it
First: fixed-period savings — the payment difference between the ARM and the fixed loan, times the months of the fixed period. That is money in hand, earned just for accepting later uncertainty. Second: the capped worst case — the ARM’s start rate plus its lifetime cap, turned into a monthly payment. If that payment would break your budget, the ARM is not a discount, it is a deferred risk; if it is absorbable and the savings are large, the ARM is a rational trade. Everything else in the debate is commentary on these two numbers. Current ARM margins, caps, and index — the ARM Index
What actually happens at adjustment
Modern agency ARMs adjust every six months after the fixed period, to the 30-day average SOFR index plus the loan’s fixed margin, rounded to the nearest eighth — bounded by a first-adjustment cap, a per-adjustment cap, and a lifetime cap (a structure like 2/1/5). The fully-indexed rate — index plus margin today — is the honest preview of where the loan is heading if the market stands still. The adjustment is arithmetic, not a lender’s mood; every input is printed in your note.
Stress-testing the “refinance before it adjusts” plan
The plan works when rates at refinance time are attractive AND you still qualify: credit intact, income stable, home value holding, debt-to-income in range. Any of those can move against you in five or seven years, and refinancing costs money each time. Two protections: pick the fixed period long enough that the plan is optional rather than mandatory (a 7- or 10-year runway instead of 5), and treat the capped worst case — not the refi plan — as your actual downside. A plan you must execute on a deadline is not a hedge; it is a bet. How locks and timing actually work
Who each loan genuinely fits
The ARM fits a defined horizon: the relocation you already expect, the starter home with a planned exit inside the fixed period, the high-income borrower who can absorb the capped case and wants the carry savings meanwhile. The 30-year fixed fits open-ended horizons and tight budgets — its premium is the price of never having to be right about rates. And when ARM and fixed pricing sit close together, take the fixed: risk that pays nothing is not worth holding. Fixed vs ARM, feature by feature
Ralo is an automated mortgage broker — not a lender — that compares multiple lenders from one application, earns a thin commission, and shows rate, APR, and fees upfront. Rates shown anywhere on this site are illustrative examples, not a loan approval, rate lock, or commitment. Available where licensed: California, Colorado, and Texas.