See your ARM payment during the fixed period, the worst case after each adjustment under your caps, and the payment if rates stay where they are.
Rates here are editable examples, not today's rates. Use the rate from your own quote or Loan Estimate.
Estimates for planning, not financial, tax or legal advice. Figures use US rules unless the page says otherwise.
How an ARM works
An adjustable-rate mortgage has a fixed rate for a set time, then the rate resets. In a 5/1 ARM the first number is the fixed period in years and the second is how often it adjusts after that, so a 5/1 is fixed for 5 years and then changes every year. Newer ARMs tied to SOFR often adjust every 6 months, written 5/6, 7/6 or 10/6.
At each reset the new rate is the index plus the margin (the fully indexed rate), limited by three caps:
- First (initial) adjustment cap: how far the rate can move at the first reset. Often 2 or 5 points.
- Subsequent cap: how far it can move at each later reset. Often 1 or 2 points.
- Lifetime cap: how far above the starting rate it can ever go. Often 5 points.
Caps are written as three numbers. 2/2/5 means 2 points at the first reset, 2 at each later one and 5 over the life of the loan. Fannie Mae's standard SOFR ARMs use 2/1/5 for a 5/6 ARM and 5/1/5 for 7/6 and 10/6 ARMs.
How it's calculated
Fixed-period payment = L × i ÷ (1 − (1 + i)−n)
Worst case at each reset: rate = min(previous rate + cap, start rate + lifetime cap)
New payment = remaining balance re-amortized over the months left
The expected path moves the rate toward the rate you enter for "index stays put", by no more than the caps allow each time.
Worked example
A $400,000, 30-year 5/1 ARM at 6% with 2/2/5 caps costs $2,398.20 a month for 5 years. In the worst case the rate goes to 8% in year 6 ($2,872.83), 10% in year 7 ($3,369.98), and 11% from year 8, the lifetime cap, at $3,623.77. If the index stays where it is and the fully indexed rate is 6%, the payment stays $2,398.20.
Limitations
- Real resets depend on the index on the change date, rounding rules and any rate floor in your note. Most standard ARMs have no floor other than the margin.
- Payment caps and negative amortization aren't modeled.
- No calculator can predict rates. The worst case shows the most your caps allow.
Sources
How we checked this
Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:
- $400,000 5/1 ARM at 6%: $2,398.20 for 5 years ✓
- 2/2/5 caps: first adjustment to 8%, $2,872.83 ✓
- Worst case at the 11% lifetime cap: $3,623.77 ✓
- 7/6 ARM with 5/1/5 caps: worst case $3,574.85 ✓
- Same, index stays at 6.75%: $2,561.58 ✓
- Fixed period as long as the term: error ✓
Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.
Questions people ask
What's the difference between 5/1, 7/1, 7/6 and 10/1 ARMs?
The first number is how many years the rate is fixed: 5, 7 or 10. The second is how often it adjusts after that: 1 means every year, 6 means every 6 months. A 7/6 ARM is fixed for 7 years, then adjusts twice a year.
How do I calculate an ARM mortgage payment?
During the fixed period it's a normal loan payment on the full term. At each reset, apply the caps to get the new rate, then re-amortize the remaining balance over the months left.
What does 2/2/5 mean on an ARM?
The rate can rise up to 2 points at the first reset, up to 2 points at each later reset, and no more than 5 points above the starting rate ever.
What is a 15/15 adjustable rate mortgage?
It's fixed for 15 years, then adjusts once and stays fixed for the last 15 years. Choose "15 years (15/15)" for the adjustment and 15 for the fixed period.
Where do I find 5/1 ARM rates today?
This site has no live rates. Use the rate on your Loan Estimate or a lender quote, then enter it here to see the payment and worst case.