How to Use the Fixed vs ARM Mortgage Comparison Tool
Choosing between a fixed rate mortgage and an adjustable rate mortgage (ARM) is one of the most important decisions you will make when buying a home. A fixed rate locks in your interest rate for the entire loan term, giving you predictable payments. An ARM offers a lower initial rate for a set period (typically 5 years), then adjusts periodically based on market rates.
Step-by-Step Instructions
- 1 Enter the home price and your down payment. The loan amount is the purchase price minus the down payment and is used for both mortgage types.
- 2 Set the fixed rate mortgage details: the interest rate and loan term (typically 30 years). This gives you the stable monthly payment baseline.
- 3 Enter the number of years you plan to stay in the home. This is the most important factor because ARMs are most beneficial for shorter stays.
- 4 Set the property tax rate for your area to get the true monthly payment including taxes.
- 5 For the ARM, enter the initial rate, the adjusted rate after the fixed period ends, the number of years the initial rate stays fixed (typically 5 for a 5/1 ARM), and the total loan term (typically 30 years).
- 6 Compare the total interest paid and remaining balance after your planned stay. The ARM saves money if you move before rates adjust but costs more if rates rise and you stay long term.
Understanding the Inputs
Home Price
Home price is the total purchase price of the property. This is used to calculate the loan amount (home price minus down payment) and the monthly property tax payment. A higher home price means a larger loan, which amplifies the interest savings or costs from choosing one mortgage type over the other. The home price is the same for both the fixed rate and ARM scenarios, allowing a direct comparison of the two mortgage types on the same property.
How to find it: Home prices are available from real estate websites like Zillow, Redfin, and Realtor.com for specific properties. For a general comparison, use the median home price in your target area. If you have a specific property in mind, use the purchase price from your offer or the listing price. Your lender will use the appraised value, which may differ from the purchase price.
Why it matters: The home price determines the magnitude of the difference between fixed and ARM mortgages. On a $200,000 home, a 1 percent interest rate difference saves about $120 per month. On a $600,000 home, that same 1 percent difference saves about $360 per month. The larger the home price, the more significant the rate difference becomes, and the more important it is to choose the right mortgage type.
Type: number · Default: 400000
Down Payment
Down payment is the amount of cash you pay upfront toward the home purchase. The loan amount is the home price minus the down payment. A larger down payment reduces your loan amount, which reduces the monthly payment and total interest for both fixed and ARM mortgages. The down payment also affects the loan to value ratio, which can influence the interest rate you qualify for on both fixed and ARM loans.
How to find it: Your down payment comes from your savings, investments, or proceeds from selling a previous home. Conventional loans require as little as 3 percent down, while FHA loans require 3.5 percent. If you put down less than 20 percent, you will need to pay private mortgage insurance. Check with your lender to determine the minimum down payment for your loan type and how your down payment amount affects your rate.
Why it matters: The down payment reduces the loan principal, which reduces the absolute dollar difference between fixed and ARM payments. A larger down payment means less money is borrowed, so the interest rate difference matters less in absolute terms. If you are putting down 50 percent or more, the difference between fixed and ARM rates becomes relatively small, making the fixed rate the simpler choice for peace of mind.
Type: number · Default: 80000
Fixed Interest Rate (%)
Fixed interest rate is the annual interest rate on a fixed rate mortgage that remains the same for the entire loan term. This is the most predictable option: your principal and interest payment never changes regardless of what happens in the economy or the bond market. Fixed rates are typically 0.5 to 1 percent higher than initial ARM rates because the lender bears all the interest rate risk over the full loan term.
How to find it: Current fixed mortgage rates are published daily on sites like Bankrate, NerdWallet, Zillow, and the Freddie Mac Primary Mortgage Market Survey. Your personal rate depends on your credit score, down payment, loan amount, and location. Rate lock periods typically range from 30 to 60 days. Get quotes from at least three lenders to find the best rate for your situation.
Why it matters: The fixed rate is the baseline against which the ARM is compared. The difference between the fixed rate and the initial ARM rate represents the upfront savings you get by choosing an ARM. If the fixed rate is 7 percent and the ARM initial rate is 6 percent, you save 1 percent interest for the first 5 years. The question is whether those savings offset the risk of higher rates later.
Type: number · Default: 7
Loan Term (Years)
Loan term for the fixed rate mortgage is the total number of years to repay the loan. The standard fixed rate mortgage term is 30 years, which offers the lowest monthly payment. Some borrowers choose 15 or 20 year terms to pay off the loan faster and pay less total interest. A shorter term has higher monthly payments but significantly less total interest and builds equity faster. The loan term affects the amortization schedule and the remaining balance after your planned years in the home.
How to find it: Mortgage terms are chosen when you apply for the loan. The most common term is 30 years because it offers the lowest monthly payment. Fifteen year terms are popular for borrowers who want to build equity faster and save on interest. Some lenders offer 20 year and 25 year terms as well. Choose a term that fits your budget and financial goals. Your lender can show you payment comparisons for different terms.
Why it matters: The loan term affects the monthly payment amount and the speed of equity building. A 30 year term has lower payments but slower equity growth, which can make the ARM comparison more interesting because the ARM savings in the first 5 years are spread across a longer term. With a 15 year term, the higher payments build equity faster, reducing the impact of the ARM adjustment because you owe less principal when rates reset.
Type: number · Default: 30
Years You Plan to Stay
Years you plan to stay in the home is the most critical input in the Fixed vs ARM comparison. This is the number of years you expect to own the home before selling or refinancing. If you plan to stay less than the ARM fixed period (typically 5 years), an ARM is almost certainly the better choice because you benefit from the lower rate and never face the adjustment. If you plan to stay much longer, a fixed rate protects you from future rate increases.
How to find it: Your planned years in the home depend on your personal circumstances. Real estate agents often recommend planning to stay 5 to 7 years to recoup transaction costs. If you are early in your career and expect to relocate, use 3 to 5 years. If you are buying a forever home and expect to stay 15 years or more, use 15 or 20 years. If you are unsure, run multiple scenarios with different stay durations to see how the comparison changes.
Why it matters: The years held is the deciding factor between fixed and ARM. If you sell before the ARM adjusts, the ARM wins because you paid a lower rate and moved before any adjustment. If you stay long after the adjustment, the fixed rate wins because the ARM rate resets higher and may stay higher for years. The breakeven point is typically around 5 to 7 years. This is why ARMs are recommended for short term homeowners and fixed rates for long term homeowners.
Type: number · Default: 7
Property Tax Rate (%)
Property tax rate is the annual percentage of your home value paid in property taxes. This is the same for both mortgage scenarios and is added to the monthly payment to give you the true cost comparison. Property taxes are determined by local governments and vary dramatically by location, from under 0.5 percent in some areas to over 2.5 percent in others. They are typically paid through an escrow account as part of your monthly mortgage payment.
How to find it: Property tax rates are set by your local county and are available on county government websites. Real estate listings show annual property tax amounts for specific properties. Your lender will estimate property taxes during the mortgage application process. If you are looking at a specific property, the listing should include the current annual property tax amount.
Why it matters: Property taxes are a significant recurring cost that adds to the monthly payment for both mortgage types. While property taxes do not affect the Fixed vs ARM comparison directly (they are the same for both), they increase the total monthly payment, which affects affordability. In areas with high property taxes, a lower ARM payment in the first 5 years can make the difference between affording and not affording the home.
Type: number · Default: 1.2
ARM Initial Rate (%)
ARM initial rate is the interest rate charged during the fixed period of an adjustable rate mortgage, typically the first 5 years for a 5/1 ARM. This rate is usually lower than a comparable fixed rate mortgage because the lender is only committing to the rate for a limited time. The initial rate is often called a teaser rate and is the primary advantage of choosing an ARM. A lower initial rate means lower monthly payments and less interest paid during the first years of the loan.
How to find it: ARM initial rates are quoted alongside fixed rates on mortgage comparison sites. The initial rate for a 5/1 ARM is typically 0.5 to 1.5 percent lower than a 30 year fixed rate. Check current ARM rates on Bankrate, NerdWallet, or the Freddie Mac survey. Your personal ARM rate depends on the same factors as a fixed rate: credit score, down payment, and loan amount.
Why it matters: The ARM initial rate is the entire reason to consider an ARM. The savings from the lower initial rate must be large enough to offset the risk of higher rates after the fixed period ends. A 1 percent lower rate on a $400,000 loan saves about $230 per month or $13,800 over 5 years. That savings is the buffer against future rate increases. The larger the difference between the fixed rate and the ARM initial rate, the more attractive the ARM becomes.
Type: number · Default: 6
ARM Adjusted Rate (%)
ARM adjusted rate is the interest rate that applies after the initial fixed period ends. For a 5/1 ARM, this is the rate your loan adjusts to after the first 5 years, and it then adjusts annually based on a benchmark index plus a margin. The adjusted rate is typically higher than the initial rate and is the risk you take with an ARM. If market rates have risen by the time your ARM adjusts, your monthly payment could increase significantly.
How to find it: The ARM adjusted rate is not known in advance because it depends on future market conditions. For the calculator, enter your best estimate of what rates will be when your ARM adjusts. You can use the current 30 year fixed rate as a conservative estimate. A common approach is to assume the adjusted rate will be equal to the current fixed rate, representing a scenario where rates stay the same. For a worst case scenario, use the fixed rate plus 2 percent.
Why it matters: The adjusted rate determines whether the ARM ends up being a good choice or a costly mistake. If the adjusted rate is only slightly higher than the initial rate, the ARM may still be cheaper than a fixed rate over the full period. If the adjusted rate jumps significantly, the ARM becomes more expensive. The comparison of total cost depends heavily on this assumption, which is why you should run multiple scenarios with different adjusted rates.
Type: number · Default: 7.5
ARM Fixed Period (Years)
ARM fixed period is the number of years the initial rate stays locked before the first adjustment. For a 5/1 ARM, this is 5 years. There are also 3/1 ARMs (3 year fixed period), 7/1 ARMs (7 year fixed period), and 10/1 ARMs (10 year fixed period). The fixed period determines how long you benefit from the lower initial rate before the rate adjusts. A longer fixed period provides more stability but typically comes with a smaller discount compared to a fixed rate.
How to find it: The ARM fixed period is specified in the loan product name and the loan contract. For this calculator, the default is 5 years, which is the most common ARM type. If you are considering a different ARM type like a 7/1 or 10/1, adjust this number accordingly. Your lender can provide quotes for different ARM types with different fixed periods.
Why it matters: The fixed period directly interacts with your planned years in the home. If your planned stay is exactly 5 years and you choose a 5/1 ARM, you benefit from the lower rate for your entire stay and face no adjustments. If you choose a 7/1 ARM and stay 5 years, you also benefit from the lower rate but may pay a slightly higher rate for the privilege of the longer fixed period. The alignment between the fixed period and your planned stay is the key to making an ARM work in your favor.
Type: number · Default: 5
ARM Total Term (Years)
ARM total term is the total number of years over which the ARM loan is amortized. Like a fixed rate mortgage, ARMs are typically 30 year loans. The total term determines the amortization schedule and the monthly payment calculation. Even though the rate adjusts, the loan is still scheduled to be fully paid off by the end of the total term. The total term is used to calculate the initial monthly payment and the amortization of the loan balance.
How to find it: The ARM total term is specified in the loan contract. Most ARMs have a 30 year term, which is the standard. Some lenders offer 15 year or 20 year ARM terms, but these are less common. The total term is typically the same for both the fixed and ARM scenarios to allow a fair comparison. Your lender will specify the available terms for the ARM product you are considering.
Why it matters: The total term affects the monthly payment amount and the speed of amortization. A 30 year ARM has lower payments but slower principal reduction, meaning you may still owe a significant balance when the rate adjusts. This can make the adjustment more painful because the higher rate applies to a larger balance. A shorter term means faster equity building, reducing the impact of rate adjustments.
Type: number · Default: 30
Tips & Best Practices
- ✓ If you plan to stay less than 5 years, an ARM is almost certainly the better choice since you benefit from the lower rate and never face the adjustment.
- ✓ If you plan to stay 10 years or more, a fixed rate mortgage is usually safer since you are protected from rate increases over the long term.
- ✓ The ARM adjusted rate is unknown. Run multiple scenarios with different adjusted rates to understand your risk.
- ✓ ARMs have annual and lifetime caps on how much the rate can increase. A typical 5/1 ARM caps annual increases at 2% and lifetime increases at 5-6%.
- ✓ Consider refinancing before the ARM adjusts. If rates are favorable, you can refinance into a new fixed rate or ARM before the adjustment hits.
- ✓ The interest rate difference between fixed and ARM changes with market conditions. When fixed rates are high, the ARM discount is often larger.
- ✓ ARMs are not bad products; they are the right choice for the right situation. Match the mortgage type to your planned time in the home.
by CalculatorPro Tools · Updated 2026-07-29