Choosing between a fixed-rate and adjustable-rate mortgage is really a question about certainty. Do you want to know your principal and interest payment for 30 years, or are you willing to take some risk for a lower starting rate?
Fixed-rate mortgages
The interest rate stays the same for the life of the loan, usually 15 or 30 years. Your principal and interest payment never changes. (Your total payment can still rise if property taxes or insurance go up.)
- Pros: predictable, simple, protects you if rates rise.
- Cons: usually a higher starting rate than an ARM; if rates fall, you have to refinance to benefit.
Adjustable-rate mortgages (ARMs)
An ARM has an initial fixed period, then the rate adjusts periodically based on a market index plus a set margin. You’ll see them described like “5/6 ARM” or “7/1 ARM”:
- The first number is how many years the rate stays fixed.
- The second is how often it adjusts after that — “6” usually means every six months, “1” means once a year.
How ARM rates change
After the fixed period, your new rate equals an index (most new ARMs use SOFR, the Secured Overnight Financing Rate) plus a margin set in your loan documents. If the index is 4% and your margin is 2.75%, your rate becomes 6.75%, subject to caps.
Rate caps: the most important part of an ARM
Caps limit how much your rate can rise. They’re often written as three numbers, such as 2/1/5:
- Initial adjustment cap (2): the most the rate can rise at the first adjustment.
- Subsequent cap (1): the most it can rise at each later adjustment.
- Lifetime cap (5): the most it can ever rise above the starting rate.
On a 5.5% ARM with a 5-point lifetime cap, your rate could someday reach 10.5%. Run that worst-case payment before you sign. The CFPB has a useful home-buying guide and ARM explainers.
When an ARM can make sense
- You expect to sell or move before the fixed period ends.
- You expect your income to rise significantly and could handle a higher payment.
- The rate gap is meaningful — a small discount isn’t worth the risk.
- You plan to pay the loan down aggressively during the fixed years.
When a fixed rate is usually the better choice
- You plan to stay in the home long-term
- Your budget has little room for payment increases
- You value predictability and don’t want to watch interest rates
- Rates are already historically low (locking in protects you)
Don’t count on refinancing
A common ARM plan is “I’ll just refinance before it adjusts.” That can work, but it depends on rates, your credit, your income, and your home’s value all cooperating at the right time. Plan as though you might have to keep the ARM.
Other ways to lower your mortgage cost
- Improve your credit before applying — see what counts as a good credit score
- Make a bigger down payment — our guide to saving for a down payment can help
- Consider buying mortgage points if you’ll keep the loan long enough
- Look into specialty programs, like VA home loans for eligible veterans
Bottom line
A fixed-rate mortgage trades a slightly higher rate for peace of mind. An ARM trades some certainty for a lower start. If you’re staying put for the long haul or your budget is tight, fixed is usually the safer pick. If you’ll likely move within the fixed period and understand the caps, an ARM can save real money. Compare Loan Estimates from several lenders side by side, and use the federal HUD site to find approved housing counselors if you want a second opinion.
