Calculate Your ARM vs Fixed-Rate Comparison
Enter your current ARM details, the lifetime interest rate cap from your loan documents, and the fixed rate you've been quoted. See exactly how much risk you're carrying and whether locking in protects you.
Your Current ARM
New Fixed-Rate Loan
How to Use This Calculator
This calculator compares three distinct scenarios for your adjustable-rate mortgage: staying at your current ARM rate, your ARM hitting its worst-case cap rate, and locking in a new fixed rate. Here is where to find each input.
Current Loan Balance. Your outstanding principal as of today. Find this on your most recent mortgage statement or by calling your servicer. Use the payoff balance, not the original loan amount.
Current ARM Rate. The interest rate your ARM is charging right now. For borrowers still in the initial fixed period, this is your original note rate. For borrowers who have passed the fixed period and are in the adjustable phase, this is your current fully-indexed rate as of your last adjustment date. Your mortgage statement will show the current rate.
ARM Lifetime Cap Rate. This is the maximum interest rate your ARM can ever reach, regardless of how much rates rise. You will find this in your original loan documents — specifically the Note or the ARM Disclosure that came with your closing package. It is often expressed as a cap above your initial rate (e.g., "5% cap" on a 5.0% initial rate means a 10.0% lifetime maximum). Enter the resulting maximum rate, not the cap percentage itself. If you cannot find your loan documents, your servicer can provide this information.
Remaining Loan Term. The total months remaining until your loan is fully paid off, assuming no additional adjustments change your amortization. This is determined by your original term minus the number of months you have been paying.
New Fixed Rate. The rate you have been quoted for a fixed-rate refinance by an actual lender. Get at least two or three quotes before entering this number. Rates for refinancing an ARM to a fixed loan are typically the standard fixed-rate market rates — they are not penalized or discounted because your current loan is an ARM.
New Fixed Loan Term and Closing Costs. Choose the term for the new fixed loan. Selecting a term that matches your remaining ARM term provides the most apples-to-apples comparison, though you may choose a shorter term to save total interest or a longer term for lower payments. Enter your expected closing costs based on actual lender quotes or estimates.
What Is an Adjustable-Rate Mortgage?
An adjustable-rate mortgage (ARM) begins with a fixed interest rate for an initial period, then adjusts periodically based on a market index plus a predetermined margin. The initial fixed period is expressed in the loan's name: a 5/1 ARM has a fixed rate for 5 years, then adjusts annually. A 7/1 ARM is fixed for 7 years, then annual adjustments. A 10/1 ARM is fixed for 10 years. After the initial fixed period, the ARM enters the adjustable phase where the rate — and therefore your monthly payment — can change each year.
The index used for adjustments has evolved over time. Older ARMs typically used LIBOR (London Interbank Offered Rate), which has been phased out and replaced primarily with SOFR (Secured Overnight Financing Rate) for most newer loans. Some ARMs use the 1-Year Constant Maturity Treasury (CMT) or the 11th District Cost of Funds Index (COFI). The margin is a fixed percentage added to the index — for example, if the index is 4.5% and your margin is 2.25%, your new rate would be 6.75%.
Why refinance an ARM to a fixed rate? Certainty. With a fixed-rate mortgage, your principal and interest payment is locked for the entire loan term — 15, 20, or 30 years, depending on which you choose. No matter what happens to interest rates, inflation, or the economy, your monthly payment obligation cannot increase. If you are in or approaching your ARM's adjustable period and rates are elevated or rising, locking in a fixed rate eliminates the risk of payment shock — the experience of seeing your monthly payment jump significantly at an adjustment date.
Understanding ARM Caps
ARM caps are your primary protection against unlimited rate increases. Your loan documents specify three types of caps that govern how much your rate can move.
Initial adjustment cap. The maximum your rate can increase at the first adjustment after the fixed period ends. Often 2% or 5% above your starting rate. A 5/1 ARM at 4.0% with a 2% initial cap can only go to 6.0% at the first adjustment, even if market rates have risen more than that.
Periodic adjustment cap. The maximum your rate can increase or decrease at each subsequent adjustment. Most commonly 2%. After the first adjustment, each annual adjustment can move your rate by at most 2% in either direction.
Lifetime cap. The maximum total increase your rate can ever reach above the starting rate, regardless of market conditions. Commonly 5% or 6% above the initial rate. A 5/1 ARM at 4.0% with a 5% lifetime cap can never exceed 9.0%, no matter what happens to interest rates over the life of the loan.
Caps are typically expressed as three numbers separated by slashes — for example, 2/2/5 means a 2% initial cap, 2% periodic cap, and 5% lifetime cap. This is the critical notation to find in your loan documents when entering the lifetime cap rate into this calculator.
How It's Calculated
The calculator computes three separate payment and interest calculations and compares them against the fixed-rate refinance option.
Max ARM Payment (cap) = P × [r_cap(1+r_cap)^n] ÷ [(1+r_cap)^n − 1]
Fixed Payment = P × [r_fixed(1+r_fixed)^n_new] ÷ [(1+r_fixed)^n_new − 1]
Rate Risk = Cap Rate − Current ARM Rate
Payment Risk = Max ARM Payment − Current ARM Payment
Where P = balance, r = monthly rate, n = remaining months, n_new = new fixed term in months
The break-even calculation compares the fixed-rate payment to your current ARM payment. If the fixed rate is higher than your current ARM rate, the break-even versus current ARM may be very long or negative — but the break-even versus the cap-rate scenario will be much shorter and more compelling. This dual perspective is the central insight of this calculator: evaluating the ARM-to-fixed decision against only your current rate understates the value of locking in.
Real-World Example
Paul's 7/1 ARM Decision
Paul has a 7/1 ARM that originated in 2017 at 4.25%. His remaining balance is $340,000 with 20 years (240 months) remaining. The ARM's 7-year fixed period ended, and he is now adjusting annually. His current rate has risen to 7.00% based on the current SOFR index plus his 2.75% margin. His ARM documentation shows a 2/2/5 cap structure: initial cap 2% (already applied at first adjustment), periodic cap 2% per year thereafter, lifetime cap 5% above the original rate = 9.25% maximum.
Current ARM payment ($340,000, 7.00%, 240 months): $2,638/mo
Maximum ARM payment ($340,000, 9.25%, 240 months): $3,116/mo
Fixed rate quoted for 20-year refinance: 6.75%
Fixed payment ($340,000, 6.75%, 240 months): $2,581/mo
Monthly savings vs current ARM: $57/mo (small)
Monthly savings vs cap-rate ARM: $535/mo (substantial)
Break-even vs current ARM ($8,000 closing costs ÷ $57): 140 months — over 11 years
Break-even vs cap-rate ARM ($8,000 ÷ $535): 15 months — well under 2 years
The decision: Against his current rate, refinancing has a poor break-even (11+ years). But Paul's ARM could still increase by up to 2.25% before hitting the lifetime cap — raising his payment by $478/month. Against the realistic worst-case scenario, the fixed rate has a compelling 15-month break-even. Paul refinances to lock in the 6.75% fixed rate, accepting a small current savings now in exchange for permanent protection against further rate increases. The psychological and financial value of payment certainty is substantial.
When ARM-to-Fixed Refinancing Makes Sense
The decision to refinance your ARM to a fixed rate is not purely mathematical — it involves risk assessment, time horizon, and personal financial tolerance. Here are the specific situations where locking in makes the strongest case.
You are approaching or past the fixed-rate period. The most critical moment to evaluate refinancing is before your ARM's fixed period expires. Once you enter the adjustable phase, your rate and payment can move each year. If rates have risen since you originated the loan, your upcoming adjustment could produce a meaningful payment increase. Many borrowers wait too long and refinance after rates have already risen — locking in a higher fixed rate than they would have secured a year earlier.
Rates are rising or elevated. If market interest rates are on an upward trend, an ARM in the adjustable phase will follow. Each periodic adjustment can add 1% to 2% to your rate, compounding over multiple adjustments until the lifetime cap is reached. Locking into a fixed rate when you believe rates will continue rising protects you from this trajectory — and even if rates eventually fall, you always have the option to refinance again if the savings justify the cost.
You plan to stay in the home for the long term. The break-even for refinancing from ARM to fixed is meaningful only if you'll be in the home long enough to recoup closing costs. If you have a 5-year plan to stay, evaluate the break-even carefully. If you plan to stay 10 or more years, locking in eliminates rate risk for a period that is essentially the rest of your planning horizon.
Payment certainty is important to your financial plan. Fixed-rate mortgages provide a foundation of certainty that makes budgeting and financial planning more reliable. For borrowers with dependents, fixed incomes, or near-retirement timelines, knowing your exact monthly housing cost for the next 20 or 30 years has genuine value that doesn't show up in a break-even calculation.
Your ARM cap rate would cause financial stress. Run your numbers: if your ARM reaches its lifetime cap rate, can you comfortably make the resulting payment? If the cap-rate payment would require significantly cutting other expenses, depleting savings, or taking on additional debt, the risk you are carrying is real. The value of refinancing is partly risk elimination — and a payment you couldn't manage at the worst case is a risk worth paying to eliminate.
When Staying in the ARM Might Make Sense
Not every ARM holder should rush to refinance. There are legitimate scenarios where staying in the ARM makes more financial sense than locking into a fixed rate.
You are still well inside the fixed period with a low rate. A borrower with a 10/1 ARM at 3.5% in year 3 has 7 more years of rate certainty. Fixed rates available today may be 6.5% or higher — locking in now at 6.5% versus keeping 3.5% for 7 more years is a poor trade even accounting for future rate risk. The ARM's current advantage is too valuable to give up prematurely.
You are planning to sell before the adjustment period begins. If you are in year 4 of a 5/1 ARM and plan to sell the home in 18 months, paying refinancing costs makes little sense. You'll sell before the ARM adjustment significantly affects you. The break-even would extend past your anticipated sale date.
Rates are expected to fall. If the economic environment suggests rates will drop in the near future, keeping the ARM means you might benefit from downward adjustments. ARMs adjust in both directions — when rates fall, your ARM rate (and payment) will also fall at the next adjustment. A fixed-rate refinance locks you into today's rate with no benefit from future rate declines without another refinance.
Common ARM-to-Fixed Scenarios
Scenario 1: 5/1 ARM in Year 4 — Act Now or Wait?
Lisa has a 5/1 ARM at 4.875% in year 4 with 26 years remaining on a $290,000 balance. The ARM adjusts in 12 months. Current fixed-rate refinance available: 6.50% for 25 years. Current ARM payment: $1,701/mo. New fixed payment: $1,951/mo. Monthly cost of locking in: $250 more per month versus current ARM rate. But if the ARM adjusts up 2% at the first adjustment (to 6.875%), her ARM payment would jump to $2,070/mo — more than the fixed payment. Lisa should refinance now, before the first adjustment, locking in at 6.50% rather than gambling on what the index does in the next 12 months. The $250 extra per month now beats the risk of $119 more per month (compared to fixed) if the ARM adjusts up by 2%.
Scenario 2: 7/1 ARM Already Adjusting Upward — Urgent Case
Michael's 7/1 ARM originated at 3.75% in 2018. He is now in the adjustable phase and his rate has risen in two successive adjustments to 7.25%. His balance is $310,000 with 18 years remaining. Current payment: $2,464/mo. His lifetime cap is 8.75% (5% above original). Cap-rate payment: $2,810/mo. Fixed rate available: 6.75% for 18 years. Fixed payment: $2,416/mo. Monthly savings vs current ARM: $48/mo (modest). Monthly savings vs cap ARM: $394/mo (substantial). Closing costs: $7,500. Break-even vs current: 156 months (13 years). Break-even vs cap: 19 months. Michael's ARM could still rise another 1.5%. The combination of upward momentum, a close lifetime cap, and a 19-month break-even against the worst case makes this an urgent refinancing situation. He should lock in now.
Scenario 3: 10/1 ARM in Year 2 — Lower Urgency, Monitor Rates
Karen has a 10/1 ARM at 5.00% originated in 2024, with 28 years remaining on a $450,000 balance. She has 8 years remaining in her fixed period. Current fixed-rate refinance: 6.625% for 28 years. Karen's current ARM payment: $2,471/mo. New fixed payment: $3,002/mo. Monthly cost to lock in: $531 more per month. Karen has 8 full years of certainty remaining at 5.00%. Locking into 6.625% now costs her $531/month more with no immediate benefit. Unless she believes rates will be dramatically higher in 8 years AND she plans to keep the home beyond the adjustment period, waiting makes more sense. She should set a calendar reminder to reassess 18 months before her fixed period expires.
Tips and Strategies
Always calculate break-even against BOTH your current ARM rate and your cap rate. The break-even against your current ARM rate alone may look poor. The break-even against your lifetime cap rate may be excellent. Both numbers are real — your current rate is what you pay today, and your cap rate is your maximum possible exposure. Presenting only one of these figures misrepresents the full value of the fixed-rate option.
Factor in the psychological value of payment certainty. This is real economic value, not just emotion. Financial planning, budgeting, family decisions, and career choices are all easier when your largest monthly expense is fixed and predictable. Many borrowers undervalue this benefit because it doesn't appear in a spreadsheet comparison. If predictability has real value in your life, account for it in your decision.
Get your fixed-rate quotes before your ARM adjusts. There is rarely a benefit to waiting until after your ARM adjustment to refinance. If you're within 12 to 18 months of your first adjustment, start the refinancing process now. Rate-locking 30 to 45 days before closing is straightforward, and you avoid any payment shock at the adjustment date.
Ask your lender if refinancing to a new ARM with a longer fixed period makes sense. In some scenarios — particularly when fixed rates are significantly higher than current ARM rates — refinancing from an expiring 5/1 ARM into a new 7/1 or 10/1 ARM at current market rates can buy you several more years of fixed-rate stability without the premium of a 30-year fixed. This works best when you are confident you won't be in the home past the new ARM's fixed period. Use the Should I Refinance Calculator to evaluate this scenario.
Consider a shorter fixed-rate term to reduce total interest. When refinancing from ARM to fixed, most borrowers automatically select a 30-year term. But if your ARM has 20 or 22 years remaining, selecting a 20-year fixed rate may offer a lower interest rate than the 30-year and aligns your payoff date more closely with your ARM's original schedule. Use the 15-Year vs 30-Year Calculator to compare term options before choosing.
Read your ARM documents to find your actual cap structure and index. Before running the numbers, pull out your original loan documents and find the Note and ARM Disclosure. These will tell you your cap structure (initial/periodic/lifetime), your index, your margin, and your adjustment dates. Guessing at these figures produces inaccurate results. Your servicer can also provide this information over the phone if you can't locate your original documents.
Frequently Asked Questions
What is a 5/1, 7/1, or 10/1 ARM?
The first number indicates how many years the interest rate is fixed at the initial rate. The second number indicates how often the rate adjusts after the fixed period ends. So a 5/1 ARM has a fixed rate for 5 years, then adjusts every 1 year thereafter. A 7/1 ARM is fixed for 7 years, then adjusts annually. A 10/1 ARM is fixed for 10 years, then adjusts annually. Some loans use 6-month adjustment frequencies (e.g., a 5/6 ARM adjusts every 6 months after year 5) — the denomination after the slash reflects months for some newer products using SOFR as the index. Always confirm the adjustment frequency in your loan documents.
How are ARM rates determined after the fixed period ends?
After the fixed period ends, your new rate is calculated by adding your loan's margin to the current value of your index at each adjustment date. The index is a market rate that reflects broad lending conditions — most newer loans use SOFR (Secured Overnight Financing Rate). Your margin is a fixed percentage written into your loan documents and never changes. For example, if SOFR is 4.5% and your margin is 2.75%, your new rate at adjustment would be 7.25%, subject to your periodic and lifetime caps. Your servicer will send you a change-of-payment notice before each adjustment showing the new rate and payment.
What are typical ARM cap structures?
The most common cap structure for 5/1 and 7/1 ARMs is 5/2/5 — meaning the initial cap is 5% (at the first adjustment), the periodic cap is 2% (at each subsequent adjustment), and the lifetime cap is 5% above the original rate. Some loans use 2/2/6 or 2/2/5 structures. A 2% initial cap is more borrower-friendly than a 5% initial cap because it limits the first-adjustment payment shock. Always read your specific loan documents rather than assuming a typical structure — cap terms are set at origination and vary by lender and product.
Should I refinance before my ARM adjusts?
In most cases, yes — refinancing before the first adjustment gives you the most control over your outcome. Once the ARM adjusts, you're responding to a higher rate rather than proactively locking in before it happens. The exception is if fixed rates are substantially higher than your current ARM rate and you believe you'll sell before the ARM adjusts significantly. In general, acting before the adjustment date gives you the ability to choose the fixed rate on your own terms and timeline rather than waiting until you're under payment pressure.
What if fixed rates are higher than my current ARM rate right now?
This is the most common objection to ARM-to-fixed refinancing. Your current ARM payment is lower, so the near-term break-even looks poor. But this calculation ignores rate risk: your ARM can and likely will increase. The right comparison is not just fixed rate versus today's ARM rate — it's fixed rate versus what your ARM rate will be in 1, 2, and 3 years if rates remain elevated or continue rising. Running the comparison against your cap rate, as this calculator does, provides the complete picture. Many borrowers find that the break-even against the cap-rate scenario is much more compelling than the break-even against today's ARM rate.
Can I refinance from one ARM to a different ARM instead?
Yes. Refinancing from an expiring 5/1 ARM to a new 7/1 or 10/1 ARM is a legitimate strategy that can provide several additional years of fixed-rate stability without committing to the premium of a 30-year fixed rate. This makes sense primarily when fixed rates are significantly higher than ARM rates (a steep yield curve environment) and when you are reasonably confident you will sell or refinance again before the new ARM's fixed period expires. It does not eliminate rate risk long-term, but it can defer it at a lower current cost than locking into a fixed rate.
Is an ARM ever the right choice?
Yes. ARMs make economic sense in specific circumstances. If you are confident you will sell the property before the fixed period ends, an ARM's lower initial rate provides real savings with no rate risk in practice. ARMs also make sense when you expect rates to fall during the ARM's adjustable period (your payments would decrease at each adjustment). They are also sometimes chosen when the rate differential versus fixed is very large, making the lower ARM rate worth accepting some future uncertainty. The key is that the decision must be made intentionally with a clear exit plan, not by defaulting to an ARM to get a lower initial payment without understanding the adjustment risk.
What is payment shock?
Payment shock refers to the experience of a sudden, large increase in your required monthly mortgage payment — typically when an ARM's rate adjusts upward significantly at the first adjustment date. For example, a 5/1 ARM originated at 3.0% with a 5% initial cap could jump to 8.0% at the first adjustment. On a $350,000 balance, that is a payment increase from $1,476/mo to $2,572/mo — a $1,096 monthly increase. This magnitude of payment change is financially destabilizing for most households and is one of the primary risks the ARM-to-fixed refinance is designed to eliminate. Regulators have introduced stress-testing requirements in lending to ensure borrowers can afford their payments at the adjustment cap rate, but understanding payment shock risk remains an important part of ARM management.
Related Calculators
These tools are useful companions to the ARM to Fixed Calculator:
- Rate-and-Term Refinance Calculator — Full analysis of any rate or term change refinance
- Should I Refinance Calculator — Quick decision framework for evaluating refinancing
- Break-Even Calculator — Dedicated break-even analysis for your refinancing scenario
- Refinance Savings Calculator — Lifetime savings modeling for any refinance scenario
- 15-Year vs 30-Year Calculator — Compare term options for your new fixed-rate loan
- Refinance Glossary — Definitions for ARM, SOFR, cap structure, and other key terms
External Resources
These authoritative sources provide additional guidance on ARM loans, rate adjustment mechanics, and refinancing decisions:
- CFPB: Loan Options — The Consumer Financial Protection Bureau's overview of mortgage loan types including adjustable-rate mortgages, cap structures, and refinancing considerations.
- HUD: Refinancing — The Department of Housing and Urban Development's consumer resources on refinancing, including guidance on switching from adjustable to fixed-rate loans.
- Federal Reserve: Interest Rate Releases — Current and historical benchmark interest rate data, useful for tracking the indices that drive ARM adjustments and understanding the fixed-rate environment.
- Freddie Mac: Refinancing Guide — Freddie Mac's educational resources on refinancing options, including the ARM-to-fixed decision and how to evaluate your options.