ARM Mortgage Calculator
Calculate payments for Adjustable Rate Mortgages with changing interest rates
Loan Details
Estimated rate after intro period
Payment Schedule
ARM Risk Assessment
• Payment increase: Moderate risk
• Best if you plan to move/refinance within 5 years
• Consider rate caps and worst-case scenarios
About ARM Mortgages
An Adjustable Rate Mortgage (ARM) features an interest rate that changes over time. ARMs typically start with a lower fixed rate for an introductory period (e.g., 5 years for a 5/1 ARM), then adjust periodically based on market rates.
How to use: Enter your loan amount, initial rate, fixed period length, expected adjusted rate, and total loan term. The calculator shows both your initial and adjusted payments, helping you evaluate affordability.
Decision factors: ARMs are best when you plan to sell or refinance before rate adjustment, expect rates to decrease, or want lower initial payments. Consider rate caps, index used, and worst-case scenarios.
About This Calculator
Calculate adjustable-rate mortgage (ARM) payments with initial fixed period, rate caps, and adjustment intervals. Compare 5/1, 7/1, and 10/1 ARM scenarios against fixed-rate mortgage alternatives.
Frequently Asked Questions
What is an ARM mortgage and how does it work?
An adjustable-rate mortgage (ARM) has an interest rate that changes periodically after an initial fixed-rate period. The notation "5/1 ARM" means 5 years fixed, then adjusts every 1 year. Common types: 3/1 ARM (3 years fixed), 5/1 ARM (most popular), 7/1 ARM, 10/1 ARM. During the fixed period, the rate is typically 0.5-1.5% lower than a comparable 30-year fixed mortgage. After the fixed period, the rate adjusts based on an index (SOFR, Treasury) plus a margin (typically 2-3%). Example: 5/1 ARM at 5.5% on $400,000 loan = $2,271/month for 5 years. If rate adjusts to 7% in Year 6, payment increases to $2,595/month. Rate caps limit how much the rate can increase per adjustment and over the life of the loan.
What are ARM rate caps and how do they protect borrowers?
ARM caps limit rate increases in three ways: (1) Initial adjustment cap — limits the first rate change after the fixed period ends. Typically 2% (a 5.5% ARM cannot exceed 7.5% at first adjustment). (2) Periodic adjustment cap — limits each subsequent annual adjustment. Typically 1-2% per year. (3) Lifetime cap — maximum rate over the entire loan term. Typically 5% above the initial rate (5.5% start = 10.5% lifetime max). Common cap structures: 2/1/5 (initial/periodic/lifetime) for conforming loans, 5/1/5 for jumbo ARMs. Example worst case: 5/1 ARM at 5.5% with 2/1/5 caps. Year 6: 7.5% (initial +2%). Year 7: 8.5% (+1%). Year 8: 9.5% (+1%). Year 9: 10.5% (+1%, hits lifetime cap). On $400,000 loan, monthly payment goes from $2,271 to $3,608 — a 59% increase. Always calculate the worst-case payment scenario before choosing an ARM.
When does an ARM make more financial sense than a fixed-rate mortgage?
ARM is advantageous in these scenarios: (1) You plan to sell or refinance within the fixed period — if you will move in 5 years, a 5/1 ARM at 5.5% vs 30-year fixed at 6.75% saves $290/month ($17,400 over 5 years) on a $400K loan. (2) You expect rates to decrease — if rates fall, your ARM adjusts downward while fixed-rate borrowers must refinance (with closing costs). (3) You can handle payment increases — higher income, significant savings, or other safety nets. (4) Large loan amounts — the rate discount on ARMs is larger for jumbo loans ($1M+ at 0.75-1.5% below fixed). ARM is risky when: you are at maximum budget with no room for payment increases, you plan to stay long-term, or rates are near historic lows (limited downside room). In 2025 with elevated rates, ARMs are popular among buyers expecting rate cuts within 3-5 years.
What index is used for ARM rate adjustments?
Most ARMs today use the Secured Overnight Financing Rate (SOFR) as their index, replacing LIBOR which was phased out in 2023. Your adjusted rate = Index + Margin. SOFR is based on overnight Treasury repurchase agreements and is considered more stable than LIBOR. Other indices include: 1-Year Treasury (CMT), 11th District Cost of Funds (COFI — West Coast), and Prime Rate (less common for mortgages). The margin is fixed at origination, typically 2.0-3.0%. Example: If SOFR is 4.5% and your margin is 2.5%, your adjusted rate = 7.0% (subject to caps). Key insight: you cannot control the index, but you can negotiate the margin. A 0.25% lower margin saves $50-100/month on a $400K loan. When comparing ARM offers from different lenders, compare the margin — it is the permanent cost difference you lock in.
How do I calculate whether to refinance out of an ARM?
Evaluate refinancing before your ARM adjusts using this framework: (1) Calculate potential adjusted payment. If your 5/1 ARM at 5.5% is approaching Year 6 and SOFR + margin = 7.5%, your $400K loan payment jumps from $2,271 to $2,763 (+$492/month). (2) Get fixed-rate refinance quotes. If 30-year fixed is 6.25%, new payment = $2,463 (saving $300/month vs adjusted ARM). (3) Factor in closing costs. Refinancing costs 1.5-3% of loan balance ($6,000-12,000 on $400K). (4) Calculate break-even: $9,000 closing costs / $300 monthly savings = 30 months. If you plan to stay 30+ months, refinancing makes sense. (5) Consider remaining loan term — refinancing into a new 30-year extends your payoff date. A 20-year or 25-year refi maintains similar payoff timeline. Alternative: if you expect rates to drop further within 1-2 years, pay the higher ARM rate temporarily rather than locking in today's fixed rate. Monitor rate trends quarterly starting 12 months before adjustment.