Fixed or adjustable: understand the tradeoff

Separate rate stability from total payment

A fixed-rate mortgage keeps its interest rate for the loan term. The scheduled principal-and-interest payment remains stable when you pay as agreed, but taxes, insurance, and other housing costs can still change. Predictability applies to the loan structure, not every cost of homeownership.

An adjustable-rate mortgage typically has an initial period before rate adjustments begin. The initial payment may look attractive, but compare what happens afterward. Your decision should account for the possibility that you remain in the home longer than expected.

Read the adjustment rules

Ask the lender to identify the reference index, margin, timing of changes, and rate caps. Have the lender show the potential payment after the first adjustment and under the maximum terms. It is easier to evaluate the risk when you can see an actual dollar amount.

A plan to move in a few years is not a guarantee. Employment, family needs, market conditions, or your equity position can change. Similarly, refinancing requires a new loan and may not be available on acceptable terms when you want it.

Compare scenarios you could live with

Run the fixed-rate payment alongside the ARM’s starting payment and a higher future payment. Ask what you would do if the payment increased and selling were inconvenient. A product is only a good fit if the range of outcomes fits your finances.

Document the tradeoff in plain language: what benefit you receive now, what uncertainty you accept later, and how you would handle it. If you cannot explain the adjustment terms, pause and ask more questions before committing.

Decode the name, the index, and the margin

A hybrid ARM’s name describes its schedule. The first number is how long the starting rate lasts; the second is how often the rate can change after that. In a 5/6 ARM (sometimes written 5/6m), the rate is fixed for five years and can then adjust every six months until the loan is paid off. An older-style 5/1 ARM adjusts once a year after five years.

At each adjustment, the new rate is the index plus the margin. The index is a market rate that moves with general conditions. The margin is a number the lender sets when you apply, and it stays the same. The CFPB points out that margins can vary a lot between lenders and can be negotiated like a fixed rate, so compare the margin, not just the starting rate.

Sources: CFPB: Consumer handbook on adjustable-rate mortgages (PDF) · CFPB: ARM index and margin

How rate caps limit each change

Caps are often written as three numbers, such as 2/1/5. In that example, the first adjustment can raise the rate by up to 2 percentage points above the starting rate, each later adjustment by up to 1 point, and the rate can never rise more than 5 points above the starting rate over the life of the loan. Your loan terms spell out the actual caps and any minimum rate.

The caps tell you the worst case, and that is the number to test against your budget. Before the first adjustment, your servicer sends notice of the new payment; the CFPB’s adjustable-rate mortgage handbook says this comes seven to eight months in advance, which gives you time to budget or shop for a new loan.

Sources: CFPB: What to look for in ARM terms · CFPB: Consumer handbook on adjustable-rate mortgages (PDF)

Worked example: five years of savings, then the reset

Take a hypothetical $400,000 loan. A 30-year fixed loan at 6.75% has a principal-and-interest payment of $2,594.39. A 5/6 ARM starting at 6.00%, with a 2.75% margin and 2/1/5 caps, starts at $2,398.20, which is $196.19 a month less. Over the first five years, the ARM charges $15,057 less interest and leaves a balance $3,286 lower ($372,217 compared with $375,503).

The table shows the payment after the first adjustment under different index values, recalculated on the remaining balance over the 25 years left. The index values are illustrations, not forecasts. The last row assumes the rate rises by the maximum allowed at every adjustment until it reaches the 11.00% lifetime cap, which in this example could happen as early as the loan’s 79th month.

The questions that decide it

How long will you keep the loan? If you are confident you will sell or refinance within the fixed period, much of the ARM’s risk may never apply. But plans change, and refinancing depends on your credit, income, home value, and rates at the time.

Could you pay the capped payment? In the example, that is $3,630.26 a month, $1,035.87 more than the fixed loan. If a payment that high would force a sale, weigh that risk heavily. Is the discount worth it to you? Here the ARM saves $196.19 a month for five years. Some borrowers reasonably choose an ARM for a known short stay or when they have strong reserves; others value never having the payment change. Write your reasoning down before you choose.

If you already have an ARM

Find your loan’s first adjustment date, index, margin, and caps in your loan documents or ask your servicer. When the notice of your new payment arrives, you typically have several months before the first higher payment is due. Use that window rather than waiting for the first bill.

You generally have three levers. You can keep the loan and build the new payment into your budget. You can make extra principal payments before the reset; because the new payment is usually recalculated on the remaining balance, a lower balance means a lower adjusted payment, so confirm how your loan handles it. Or you can compare refinance quotes, keeping in mind that approval and pricing depend on your credit, income, and home value at the time.

Sources: CFPB: Consumer handbook on adjustable-rate mortgages (PDF)

Reading the ARM terms on your Loan Estimate

When a loan’s rate can rise after closing, the Loan Estimate must include an Adjustable Interest Rate (AIR) table in its closing cost details. It lists the index and margin, the initial rate, the minimum and maximum rates, how often the rate adjusts, and the limits on each change. The loan terms on page 1 also answer whether the interest rate and the monthly principal and interest can increase after closing.

Compare those entries with what the loan officer told you and with your own notes: the margin and caps should match your quote exactly. If two offers use different indexes or caps, compare their payments at the maximum rate rather than their starting rates. Keep the AIR table with your records so you can check each future adjustment notice against it.

Sources: CFPB: Regulation Z § 1026.37, Loan Estimate contents · CFPB: Loan Estimate explainer

Your next-step checklist

• Get the index, margin, adjustment schedule, and caps in writing.
• Compare the margin across lenders, not only the starting rate.
• Ask for payment examples after the first adjustment and at the lifetime cap.
• Test your budget against the capped payment.
• Include a stay that runs longer than you plan.
• Compare five-year interest and balances with a fixed-rate quote.