How Fixed-Rate Mortgages Work
With a fixed-rate mortgage, your interest rate stays the same for the entire life of the loan. This means your principal and interest payment remains stable, making it easier to budget over the long term. Fixed-rate mortgages are commonly available with 15-year or 30-year terms, though 10-year and 20-year options also exist.
- Interest rate is locked for the full loan term.
- Monthly principal and interest payments are predictable and consistent.
- Common terms include 15, 20, 30 years, but other lengths may be available.
Sources: Freddie Mac, Lower
How Adjustable-Rate Mortgages (ARMs) Work
An adjustable-rate mortgage has an interest rate that is fixed for an initial period—commonly 3, 5, 7, or 10 years—and then adjusts periodically. The adjustment is based on a market index plus a lender-set margin, subject to rate caps that limit how much the rate can change. For example, a 5/1 ARM has a fixed rate for the first five years and then adjusts once per year for the remaining loan term.
Most ARMs include both periodic caps (limits on how much the rate can increase in a single adjustment) and lifetime caps (limits on the total increase over the life of the loan).
- Initial fixed period: often 3, 5, 7, or 10 years
- Adjustment frequency: commonly annual after the initial period
- Rate determined by index + margin, with caps to limit changes
Sources: Freddie Mac, Lower, MortgageCalculator.org
Fixed-Rate vs ARM: Side-by-Side Comparison
The table below summarizes the key differences between fixed-rate and adjustable-rate mortgages based on rate stability, payment predictability, initial rate, lifetime interest, and risk of rate increases.
| Feature | Fixed-Rate Mortgage | Adjustable-Rate Mortgage (ARM) |
|---|---|---|
| Interest rate stability | Fixed for entire loan term | Fixed for initial period, then adjusts periodically |
| Payment predictability | Stable principal and interest payment | Stable during initial period, then may change |
| Initial rate | Often higher than comparable ARM introductory rate | Often lower than fixed-rate mortgage rates |
| Lifetime interest | Total interest is set at origination; longer terms lead to more total interest | Total interest depends on future rate path; could be lower or higher |
| Risk of rate increases | No risk of payment increase due to rate changes | Payments can increase after the initial fixed period, limited by caps |
| Rate adjustments | None | Based on index plus margin with caps |
| Best for | Long-term homeowners, predictable budgeting | Short-term homeowners, those expecting to move or refinance |
Sources: Freddie Mac, Lower
Pros and Cons of Fixed-Rate Mortgages
Fixed-rate mortgages offer payment stability, which is helpful if you plan to stay in your home for many years and prefer predictable budgeting. However, the initial interest rate is often higher than an ARM’s introductory rate, and you won’t benefit from market rate decreases unless you refinance.
- Pros: Stable payments for the life of the loan; easier to plan long-term budgets; no risk of payment increases due to rate adjustments.
- Cons: Typically higher initial rate compared to ARM intro period; you may miss out on lower payments if market rates fall without refinancing.
Sources: Freddie Mac, Lower
Pros and Cons of Adjustable-Rate Mortgages
Adjustable-rate mortgages often start with lower initial payments, which can be attractive if you plan to sell or refinance before the adjustment period ends. However, after the initial fixed period, your rate can increase, and monthly payments may become less predictable. Caps limit how much the rate can change, but significant increases are possible.
- Pros: Lower initial rate and payment; can be advantageous for short-term ownership; caps provide some protection against extreme rate spikes.
- Cons: Payments can increase after the initial period; more risk and uncertainty over the long term; not ideal if you plan to stay past the fixed period without being prepared for adjustments.
Sources: Freddie Mac, Bankrate, Lower
When a Fixed-Rate Mortgage Makes Sense
A fixed-rate mortgage may be a suitable choice if you plan to stay in your home for a longer period—roughly 10 years or more—and you value payment stability. This approach can protect you from potential future rate increases, making long-term budgeting easier.
Sources: Freddie Mac
When an Adjustable-Rate Mortgage Makes Sense
An ARM may make sense if you plan to sell your home within a short time, typically before the initial fixed period ends. Because ARMs often have lower introductory rates, you can take advantage of lower initial payments during the time you expect to own the property. However, be aware that after that period, rates—and your monthly payment—could increase.
Sources: Freddie Mac, Bankrate, Lower
Using a Mortgage Calculator to Compare Both Types
Mortgage calculators can help you estimate monthly payments for both fixed-rate and adjustable-rate loans. For a fixed-rate mortgage, you can use the loan amount, interest rate, and term to calculate a consistent payment. For an ARM, you can calculate payments during the initial fixed period using the introductory rate, and then model potential payments after adjustments using different index-plus-margin scenarios. Comparing these estimates helps you see the trade-offs between lower initial payments and potential future increases.
Because ARM rates depend on a market index and a lender-set margin, the final adjustments will vary by lender and market conditions. Always consult a lender for current rates and specific loan terms.
- Fixed-rate: Use loan amount, rate, and term to find the stable monthly payment.
- ARM: Estimate initial payments using the intro rate, then model possible adjustments after the fixed period.
- Compare total costs over your expected ownership period to see which type may be more cost-effective.
Sources: MortgageCalculator.org, Freddie Mac, Lower
Frequently asked questions
What is the typical adjustment cap for an ARM?
Most ARMs have limits on how much the interest rate can go up or down within an adjustment period, called periodic caps, as well as lifetime caps that limit the total increase over the life of the loan. The specific cap figures vary by loan and lender, so you’ll need to check the terms of each ARM offer.
Sources: Freddie Mac, LowerHow often can an ARM rate change?
After the initial fixed period, an ARM rate typically adjusts once a year. For example, a 5/1 ARM has a fixed rate for the first five years and then adjusts annually for the remaining loan term.
Sources: Freddie Mac, LowerCan I convert an ARM to a fixed-rate loan later?
Conversion options vary by lender and loan product. Some ARMs may include a conversion feature, but it is not guaranteed. Check your loan agreement or speak with your lender to see if conversion is available for your specific mortgage.
Sources: LowerDo ARMs always have lower initial payments?
ARM rates typically start off lower than fixed-rate mortgage rates, which can result in lower initial monthly payments. However, this is not guaranteed for every loan; the introductory rate is set by the lender and may be competitive with or without a discount. It’s important to compare offers.
Sources: Freddie Mac, Bankrate, LowerWhat index is commonly used for ARMs?
The index used for ARM adjustments varies by lender and loan program. Your lender will specify which market index your ARM is tied to, along with the margin and caps that determine rate changes.
Sources: LowerSources
- Choosing Between a Fixed-Rate and an Adjustable-Rate Mortgage - My Home by Freddie Mac — Freddie Mac
- Considering a Fixed-Rate Mortgage? Here’s What You Should Know — Freddie Mac
- Fixed-Rate Mortgage vs. ARM: What's the Difference? — Bankrate
- ARM vs Fixed Rate Mortgage Calculator — MortgageCalculator.org
- Adjustable-Rate vs. Fixed-Rate Mortgages | Lower Mortgage — Lower