The adjustable rate saves you a point against the fixed, and the loan officer explains that you will refinance long before it adjusts. Both statements are true. Neither answers the only question that matters: if you are still holding this loan in year eleven, what is the highest payment the contract permits?
You’ll learn how to read a cap structure, how the index and margin set your rate after the fixed period, and how to calculate your worst case in about two minutes.
Reading the Name
A 5/6 ARM is fixed for five years, then adjusts every six months. A 7/6 is fixed for seven. The older 5/1 notation meant annual adjustments after the fixed period; most current products adjust semi-annually, which means twice the opportunities to move.
After the fixed period your rate is rebuilt from two components at every adjustment: an index, which moves with the market, plus a margin, which is fixed in your contract and never changes. The index is typically SOFR-based on current products. The margin is the lender’s spread, commonly around two to three percentage points.
The Three Numbers That Cap It
A cap structure written as 2/1/5 means three separate limits:
| Position | Name | What it limits |
|---|---|---|
| First | Initial cap | How much the rate can move at the first adjustment |
| Second | Periodic cap | How much it can move at each subsequent adjustment |
| Third | Lifetime cap | Total increase permitted above the starting rate, ever |
So a 5/6 ARM starting at 5.75% with 2/1/5 caps can reach 7.75% at the first adjustment, then move a further point every six months, up to a maximum of 10.75% for the remaining term.
| Scenario | Rate | Monthly P&I on $300,000 |
|---|---|---|
| Starting rate | 5.75% | $1,751 |
| After first adjustment, capped | 7.75% | $2,149 |
| Lifetime maximum | 10.75% | $2,800 |
That is the number to sit with: $1,751 today, $2,800 permitted. Model your own loan at both ends in our mortgage calculator. If the maximum is a payment you could not make, the discount today is not a saving — it is a deferred risk.
Why the Refinance Plan Is Not a Plan
Most ARM borrowers intend to refinance or sell before the fixed period ends. Frequently they do. The plan fails in the specific circumstance where the ARM hurts most, and the failure modes correlate.
If rates have risen, your ARM adjusts upward and refinancing offers nothing better. If your income has fallen or your employment changed, you may not qualify to refinance at all — the file is re-underwritten from scratch, as our guide to what lenders re-verify sets out. If property values have fallen, your loan-to-value may block it. And a refinance costs 2% to 5% in closing costs, which our piece on the break-even month shows can take years to recover.
The honest test is whether you could hold the loan at its cap. Not whether you expect to.
When an ARM Genuinely Fits
A defined short horizon. Military orders, a fixed-term contract, a training programme with a known end date. The fixed period covers the whole occupancy.
Income you expect to rise substantially. A borrower early in a career with a predictable earnings curve can reasonably carry the risk of a higher payment later.
You could pay it off at the reset. Where the balance is small relative to assets, an adjustment is an inconvenience rather than a threat.
The spread against fixed is wide. The trade only makes sense when the discount is real. Compare against the current 30-year fixed on our daily rates page — at 6.55% on July 20, 2026, an ARM priced within a quarter point of fixed is taking risk for very little.
Four Questions Before You Sign
What is my margin, and is it negotiable? What are the three caps? Is there a floor rate below which my rate cannot fall — many ARMs have one, which limits the upside if rates drop. And does the loan carry a prepayment penalty, which would make the refinance exit expensive at exactly the wrong time?
All four answers are in the note and the disclosures. Ask for them in writing before you are at the closing table, where reviewing a cap structure under time pressure is how people end up surprised in year six.
The bottom line
- After the fixed period, your rate is an index that moves plus a margin that never does.
- A 2/1/5 cap structure limits the first adjustment, each later one, and the lifetime increase.
- A 5.75% start with 2/1/5 caps permits 10.75% — on $300,000 that is $1,751 rising to $2,800.
- The refinance exit fails precisely when rates rise, income falls, or values drop.
- Ask for the margin, the caps, any rate floor and any prepayment penalty in writing before closing.
Frequently Asked Questions
What do the numbers in 2/1/5 caps mean?
The first limits the initial adjustment, the second limits each subsequent adjustment, and the third caps the total increase above your starting rate for the life of the loan.
What is the margin on an ARM?
A fixed percentage added to the index at every adjustment to set your rate. It never changes over the life of the loan, which is why it is worth asking whether it can be negotiated.
Can my ARM rate go down?
Yes, if the index falls, though many ARMs include a floor below which the rate cannot drop. Check whether yours has one.
Is an ARM a bad idea?
Not inherently. It suits a defined short horizon or a borrower who could absorb the capped payment. It becomes risky when the plan depends on refinancing, since that option can disappear exactly when the rate rises.
Sources & further reading:
Consumer Financial Protection Bureau,
30-year conforming rate lock index via FRED.
