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The Finance Base
adjustable-rate mortgages

How to Compare a Fixed-Rate Mortgage With an Adjustable-Rate Mortgage

Compare fixed-rate and ARM mortgage offers on equal terms, then check the ARM’s reset schedule, caps, fees, and highest permitted payment before deciding.

By TheFinanceBase Team 5 min read
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Compare written fixed-rate and adjustable-rate mortgage offers for the same loan amount, down payment, term, property assumptions, and borrower profile. A fixed-rate loan keeps its interest rate constant; an adjustable-rate mortgage (ARM) can start with a fixed introductory rate and then change on a schedule set by the contract. Look beyond the initial payment: compare fees and APR, learn how the ARM resets, and check whether you could afford its highest permitted payment.

What is the difference between a fixed-rate and adjustable-rate mortgage?

With a fixed-rate mortgage, the interest rate stays the same for the loan term, so the principal-and-interest payment is predictable. An ARM typically has an initial fixed-rate period followed by rate adjustments at intervals specified in the contract. Its rate and principal-and-interest payment can rise or fall as the loan adjusts.

The total amount you pay each month may also include property taxes, homeowners insurance, and mortgage insurance. Those costs can change even when your mortgage interest rate is fixed, and they may be collected separately from the lender’s principal-and-interest payment. See the CFPB’s fixed-rate and ARM explanation and overview of mortgage loan types.

How do I compare a fixed mortgage with an ARM?

Ask multiple lenders for written Loan Estimates based on the same scenario. The Consumer Financial Protection Bureau (CFPB) recommends comparing at least three offers. Quotes with different loan amounts, terms, points, or fees—or quotes from different dates—are not direct comparisons. Use the Loan Estimate to examine both the loan terms and the costs, rather than choosing from an advertised rate alone. The CFPB explains what to compare when shopping for a mortgage and how to compare Loan Estimates.

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1. Match the assumptions

  • Use the same loan amount, down payment, repayment term, property assumptions, and borrower profile for each offer.
  • Record when each offer was quoted and whether it includes discount points or other charges that affect the rate.
  • Request written Loan Estimates from at least three lenders so you can compare documented offers.

2. Compare the starting costs and payment

For each estimate, note the interest rate, initial principal-and-interest payment, points, lender fees, and APR. Check which costs the displayed payment includes: taxes, homeowners insurance, and mortgage insurance can be separate or may change over time.

APR is a broader measure than the note interest rate because it includes certain loan charges. But an ARM’s APR does not show its maximum possible rate, so neither APR nor the introductory rate alone tells you how high the payment could go. The CFPB explains the difference between a mortgage interest rate and APR.

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3. Decode the ARM schedule

Write down the length of the initial fixed-rate period, the first adjustment date, and how often the rate can adjust afterward. In a 5/1 ARM, the “5” generally means the initial rate period lasts five years, while the “1” indicates that the rate adjusts every year after that period. Verify the schedule in the actual loan terms; notation alone is not a substitute for the contract. The CFPB defines 5/1 ARM and other mortgage terms.

Also identify the index and margin. After the initial period, the rate is generally based on the index plus the lender-set margin, subject to the contract’s caps. An index can move with market conditions; the margin is specified in the agreement. Check which index applies and how the contract uses it. See the CFPB’s explanation of ARM indexes and margins.

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4. Find the ARM’s payment ceiling

Record the initial, subsequent, and lifetime rate caps. An initial cap limits the first adjustment, a subsequent cap limits later adjustments, and a lifetime cap limits how far the rate may rise over the life of the loan. The actual limits vary by offer, so read the contract rather than relying on a typical example.

Ask the lender to calculate the highest payment the loan permits under its terms. Consider whether you could afford it if your income changed or your plans did not work out. The CFPB advises borrowers to check ARM rate caps and ask about the maximum payment.

5. Check how payments and balances are recalculated

Ask when the payment is recalculated and whether it changes at every rate adjustment. Check for a floor, which can prevent the interest rate from falling below a contractually specified level. Find out whether payment limits could cause the unpaid interest to be added to the balance—a possibility known as negative amortization—and whether the contract permits it. Review any prepayment penalty as well. The CFPB lists ARM fine-print details to check.

6. Compare the complete offers

Review the written costs and terms alongside the rate and payment. Ask lenders whether they can improve an offer, and compare any lower rate against the points or other charges required to obtain it. Treat an ARM’s starting payment as only one part of the comparison; the adjustment terms determine how the loan can change later.

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How much can my ARM payment go up?

There is no single increase that applies to every ARM. The loan’s initial, subsequent, and lifetime caps, adjustment schedule, index, margin, balance, and payment-recalculation rules determine how the rate and payment can change. Ask the lender for the highest payment allowed by your specific contract rather than estimating the risk from the introductory rate or from a generic ARM example.

Should I choose a fixed-rate mortgage or an ARM?

A fixed-rate offer may fit a borrower who values payment predictability and expects to keep the loan for a long time. An ARM may merit comparison if its initial offer is attractive and the borrower can handle both rate uncertainty and the contract’s maximum payment. These are factors to weigh, not a universal recommendation; compare the written terms and your capacity to manage the payment risk.

Do not base affordability on an assumed sale or refinance before the first adjustment. The CFPB warns: “Don’t assume you’ll be able to sell your home or refinance your loan before the rate changes.” The agency’s consumer guidance was last reviewed January 14, 2025. Its historical selection figures—85–95% of buyers choosing fixed-rate mortgages and 5–15% choosing ARMs from 2008–2022, compared with 70–75% fixed-rate and 25–30% ARM before 2008—are historical ranges, not current market shares or a prediction of what borrowers will choose. For more on how ARM payments may change over time, see the CFPB’s ARM handbook.

This comparison is general U.S. consumer guidance, not a recommendation for an individual household. Rates and payments vary by location, borrower, lender, loan structure, date, points, and fees; the written offer and loan contract control the actual terms.

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