Mortgage Rates Explained: Fixed vs Adjustable

Your mortgage interest rate is arguably the single most important number in your home purchase. A difference of just half a percentage point on a $400,000 loan can cost or save you tens of thousands of dollars over the life of the loan. Yet many homebuyers accept whatever rate their lender offers without fully understanding what drives it or whether a different type of mortgage might be a better fit.

This guide breaks down how mortgage rates are determined, the key differences between fixed-rate and adjustable-rate mortgages, and strategies like rate locks and discount points that can help you secure the best deal.

How Mortgage Rates Are Determined

Mortgage rates are influenced by a combination of macroeconomic factors and your personal financial profile. Understanding both gives you a clearer picture of what you can expect and what you can control.

Macroeconomic factors include the Federal Reserve's monetary policy, inflation expectations, the bond market (particularly the yield on the 10-year U.S. Treasury note), and overall economic conditions. When the economy is strong and inflation is rising, rates tend to climb. When economic growth slows or the Fed cuts its benchmark rate, mortgage rates often decrease, though not always in lockstep.

Personal factors that lenders evaluate include your credit score, down payment size, debt-to-income ratio (DTI), loan amount, and the type of property you are buying. A borrower with a 780 credit score putting 20% down will typically qualify for a significantly lower rate than someone with a 650 score putting down 5%.

• Credit score: The most influential personal factor. Scores above 740 generally qualify for the best rates. Every 20-point drop can add 0.125% to 0.25% to your rate.
• Down payment: Putting down 20% or more eliminates private mortgage insurance (PMI) and typically earns you a better rate because the lender faces less risk.
• Debt-to-income ratio: Lenders prefer a DTI below 36%, though many will approve loans up to 43% or even 50% with compensating factors.
• Loan type: Conventional loans, FHA loans, VA loans, and jumbo loans each carry different rate structures.

Fixed-Rate Mortgages

A fixed-rate mortgage locks in your interest rate for the entire life of the loan. Whether you choose a 15-year or 30-year term, your monthly principal and interest payment never changes. This predictability is the primary appeal.

30-year fixed is the most popular mortgage product in the United States by a wide margin. It offers the lowest monthly payment of any fixed-rate option, though you pay more total interest over the life of the loan. As of early 2025, 30-year fixed rates hover in the 6.5% to 7.0% range for well-qualified borrowers.

15-year fixed mortgages carry lower interest rates (typically 0.5% to 0.75% less than the 30-year) and save you a substantial amount of interest. The trade-off is a significantly higher monthly payment. On a $350,000 loan at 6.5%, a 30-year mortgage costs about $2,212 per month, while a 15-year mortgage at 5.9% costs about $2,937 per month but saves you over $190,000 in total interest.

Best for: Buyers who plan to stay in their home long-term, who value payment stability, or who are buying in a low-rate environment and want to lock in the savings.

Adjustable-Rate Mortgages (ARMs)

An adjustable-rate mortgage offers a lower introductory rate for a fixed initial period, after which the rate adjusts periodically based on a market index plus a margin set by the lender.

ARM naming follows a simple pattern: a 5/1 ARM means the rate is fixed for the first 5 years, then adjusts once per year. A 7/6 ARM means the rate is fixed for 7 years and adjusts every 6 months after that. Common structures include 3/1, 5/1, 5/6, 7/1, 7/6, and 10/1 ARMs.

ARMs come with rate caps that limit how much your rate can increase:

• Initial adjustment cap: The maximum the rate can rise at the first adjustment (commonly 2% to 5%).
• Periodic adjustment cap: The maximum increase at each subsequent adjustment period (commonly 1% to 2%).
• Lifetime cap: The absolute maximum the rate can ever reach over the life of the loan (commonly 5% above the initial rate).

Best for: Buyers who plan to sell or refinance before the initial fixed period ends, borrowers in high-rate environments who expect rates to fall, or those who can tolerate payment variability in exchange for lower initial costs.

Rate Locks: Protecting Your Rate

A rate lock is an agreement between you and your lender that guarantees a specific interest rate for a set period, typically 30 to 60 days, while your loan is being processed. This protects you from rate increases between the time you apply and the time you close.

Most rate locks are free for 30 to 45 days. Extending the lock period (to 60 or 90 days) may cost a small fee, usually 0.125% to 0.25% of the loan amount. If rates drop after you lock, some lenders offer a float-down option that lets you take the lower rate, though this typically comes with additional cost.

When to lock: Lock when you are comfortable with the rate and have a realistic closing timeline. If your lock expires before closing, you may face a higher rate or extension fees.

Mortgage Points: Buying Down Your Rate

Discount points are upfront fees you pay to the lender at closing in exchange for a lower interest rate. One point equals 1% of the loan amount and typically reduces your rate by about 0.25%, though the exact amount varies by lender and market conditions.

For example, on a $400,000 loan, one point costs $4,000. If it reduces your rate from 7.0% to 6.75%, your monthly payment drops from $2,661 to $2,594, saving $67 per month. You would break even in about 60 months (5 years). If you plan to stay in the home longer than that, buying points makes financial sense.

Tip: Points are typically tax-deductible in the year you purchase the home, which effectively reduces their cost. Consult a tax professional for your specific situation.

Fixed vs. ARM: A Side-by-Side Comparison

The right choice depends on your timeline, risk tolerance, and the current rate environment. Here is how they stack up:

• Payment stability: Fixed-rate wins. Your payment never changes. ARM payments can rise substantially after the initial period.
• Initial rate: ARMs win. The introductory rate is typically 0.5% to 1.5% lower than the comparable fixed rate.
• Total cost (short-term): ARMs often win if you sell or refinance before the first adjustment.
• Total cost (long-term): Fixed usually wins, especially if rates rise during the adjustable period.
• Refinancing flexibility: Roughly equal, though ARM holders may feel more pressure to refinance before adjustments begin.

How to Get the Best Mortgage Rate

Regardless of which type of mortgage you choose, these strategies can help you secure the lowest rate possible:

• Improve your credit score: Pay down credit card balances, avoid new credit inquiries, and dispute any errors on your credit report before applying.
• Save for a larger down payment: 20% down eliminates PMI and qualifies you for better rates.
• Shop multiple lenders: Get quotes from at least 3 to 5 lenders, including banks, credit unions, and online lenders. Rate differences of 0.25% to 0.5% between lenders are common.
• Consider shorter loan terms: A 15-year mortgage carries a lower rate than a 30-year.
• Buy points if you are staying long-term: Calculate your break-even point and buy points if it makes sense for your timeline.

Use our mortgage calculator to compare monthly payments and total interest costs across different rates, terms, and down payment amounts.

The Bottom Line

There is no universally "best" mortgage type. A fixed-rate mortgage gives you certainty and is the safer choice for most homebuyers, especially those planning to stay put for more than 7 years. An ARM can save you money if you are confident you will move or refinance before the rate adjusts.

Whatever you choose, the most important step is shopping around. Even a small rate difference adds up to real money over the life of a mortgage. If you are just beginning your homebuying journey, our first-time homebuyer guide walks you through the full process from pre-approval to closing day.