ARM Payment Calculator
Calculate adjustable rate mortgage payments with initial fixed rate, adjustment caps, and worst-case payment scenarios for 5/1 ARM structures.
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Visualization
How It Works
An adjustable rate mortgage (ARM) offers a lower initial interest rate for a fixed period (typically 5, 7, or 10 years), then adjusts periodically based on a market index plus a margin. A 5/1 ARM means 5 years fixed, then adjusting annually. Rate caps limit how much the rate can change at each adjustment and over the life of the loan. ARMs carry the risk of payment increases but offer initial savings compared to fixed-rate mortgages.
The Formula
Post-Adjustment: Recalculate with new rate on remaining balance for remaining term
Caps: 2/2/5 means first adjustment max +2%, subsequent +2% each, lifetime max +5%
Variables
- 5/1 — ARM structure: 5 years fixed, then adjusts every 1 year
- 2/2/5 — Typical cap structure: 2% first adjustment, 2% periodic, 5% lifetime maximum over initial rate
- Index — Market rate the ARM is tied to (commonly SOFR), plus a lender margin (typically 2-3%)
- Margin — Fixed percentage added to the index to determine your rate at each adjustment
Worked Example
A $350,000 5/1 ARM at 5.5% initial rate with 2/2/5 caps: Initial payment = $1,987/month. After 5 years, balance is about $323,000. If rate jumps 2% to 7.5%, payment becomes $2,503. Worst case at 10.5% (lifetime cap), payment would be $3,173. A 30-year fixed at 6.5% would be $2,212/month from day one.
Practical Tips
- ARMs make the most sense if you plan to sell or refinance before the fixed period ends.
- Always calculate your worst-case payment at the lifetime cap to make sure you can afford it if rates rise.
- The initial rate savings versus a fixed rate can be invested or used for extra principal payments during the fixed period.
- SOFR (Secured Overnight Financing Rate) has replaced LIBOR as the standard ARM index. Understand which index your ARM uses.
- A 7/1 or 10/1 ARM offers more years of rate certainty than a 5/1 ARM, though the initial rate will be slightly higher.
Frequently Asked Questions
What does 5/1 ARM mean?
The first number (5) is how many years the initial rate is fixed. The second number (1) is how often the rate adjusts after that. So a 5/1 ARM has a fixed rate for 5 years, then adjusts every year. Other common structures are 7/1 and 10/1.
What are rate caps?
Rate caps limit how much your interest rate can change. Typical caps are 2/2/5: the rate can increase a maximum of 2% at the first adjustment, 2% at each subsequent adjustment, and 5% total over the life of the loan. For example, a 5.5% initial rate with a 5% lifetime cap can never exceed 10.5%.
Can my ARM payment decrease?
Yes, if interest rates drop, your ARM rate can decrease at adjustment time, lowering your payment. The rate cannot drop below the floor (usually the margin rate). This is an advantage of ARMs when rates are falling.
Should I choose an ARM or fixed rate?
Choose an ARM if you plan to move or refinance within the fixed period, or if you believe rates will decrease. Choose fixed if you want payment certainty, plan to stay long-term, or cannot afford the worst-case ARM payment.
What index is used for ARM adjustments?
Most new ARMs use SOFR (Secured Overnight Financing Rate) as the index. Your rate at each adjustment equals the index value plus your margin. For example, if SOFR is 4% and your margin is 2.75%, your adjusted rate would be 6.75% (subject to caps).