The trade you are actually making
An ARM sells you a lower rate today in exchange for rate risk later. That is the entire product. The lender can offer 5.75% when the 30-year fixed costs 6.75% because after the fixed period the market risk becomes your problem instead of theirs.
The machinery has three parts. The fixed period, usually 3, 5, 7, or 10 years, is when the rate holds. The formula, index plus margin, generates each new rate afterward: the index (SOFR on nearly all modern ARMs) moves with the market, while the margin is a fixed spread the lender sets at closing. And the caps bound how far each reset can go. Lenders must disclose all of this before closing, and the CFPB's home loan toolkit shows where each number lives in your Loan Estimate.
Whether the trade is smart depends almost entirely on your timeline. A buyer who sells in year four of a 5/1 ARM banked the discount and never touched the risk. A buyer still in the house in year twelve has ridden seven resets. Neither outcome says anything about the other buyer's decision; they were holding different positions.
Reading 2/2/5, the three numbers that bound your risk
Rate caps are the difference between an uncomfortable reset and a catastrophic one, and they come written as three numbers like 2/2/5. The first is the initial cap: the most the rate can rise at the first adjustment. The second is the periodic cap, applied to each adjustment after that. The third is the lifetime cap, the ceiling above the starting rate for as long as the loan exists.
Apply 2/2/5 caps to a 5/1 ARM that opens at 5.75% and the worst case traces out cleanly, one adjustment at a time.
| Stage | Cap that applies | Maximum rate |
|---|---|---|
| Years 1 to 5 | None, rate is fixed | 5.75% |
| First adjustment, year 6 | Initial cap, 2% | 7.75% |
| Second adjustment, year 7 | Periodic cap, 2% | 9.75% |
| Third adjustment, year 8 | Lifetime cap, 5% | 10.75% |
| Year 9 onward | Lifetime cap, 5% | 10.75% |
Worst-case rate path on a 5/1 ARM starting at 5.75% with 2/2/5 caps.
- The periodic cap alone would allow 11.75% at the third adjustment, but the lifetime cap holds the rate at 10.75% no matter what the index does.
- Caps limit the rate, not the payment. A capped rate on a large balance can still produce a payment well above what you started with.
- Cap structures vary. A 5/2/5 ARM allows a 5% jump at the first reset, so two loans with the same teaser rate can carry very different risk.
Run the worst case before you sign
Take the calculator's defaults: a $320,000 loan, 5.75% fixed for five years, 2/2/5 caps. The initial payment is about $1,867. After five years of payments the balance sits near $297,000, and that balance is what reprices.
If rates run straight to the caps, the rate hits 7.75% in year six, 9.75% in year seven, and the 10.75% ceiling in year eight. In round numbers, the payments on that repricing balance land near $2,240, then $2,650, then $2,860. The last figure is roughly $1,000 a month above where you started. That is the scenario the caps permit, and while the full climb requires a sustained rate spike, borrowers who closed ARMs in 2020 and reset in 2023 can confirm that spikes happen on exactly this schedule.
So stress the budget honestly. Could you carry the payment at the lifetime cap? If a refinance were blocked by falling values or a rough patch at work, could you carry it for two or three years? On these numbers a 30-year fixed at 6.75% costs $2,076, about $209 a month more than the ARM's teaser. If the cap-rate payment would break you, that $209 is what insurance against it costs. The CFPB publishes a plain-language guide to ARM disclosures and what they must tell you before closing, including the worst-case examples lenders are required to show.
The five-year head start, measured against a fixed loan
Put the same $320,000 loan under both products: a 5/1 ARM at 5.75% against a 30-year fixed at 6.75%. The fixed loan costs $2,076 a month. The ARM costs $1,867, so it saves $209 a month for sixty months, about $12,540. The ARM also retires principal faster during those years because less of each payment goes to interest, so after five years its balance sits near $297,000 against roughly $300,400 on the fixed loan. Call the total head start $16,000.
Now let the ARM adjust to 7.75%. The new payment on the remaining balance is about $2,240, which is $166 a month more than the fixed loan. At that pace the ARM burns through its $16,000 advantage in roughly eight years, meaning the two borrowers break even somewhere around year thirteen. If the rate resets lower or you exit the loan before the advantage runs out, the ARM won. If rates run to the cap, the advantage disappears in under three years of resets.
The comparison always turns on the same question: will you still hold this loan when the higher payments have eaten the head start? Buyers confident they will move or refinance within five to seven years usually come out ahead with the ARM. Buyers settling in for the long haul are usually paying the fixed-rate premium for something they genuinely need.