A fixed-rate mortgage keeps the same note interest rate for its contractual term, making scheduled principal-and-interest payments predictable.
A fixed-rate mortgage is a mortgage whose note interest rate remains unchanged for the contractual loan term. On a standard fully amortizing loan, that fixed rate produces a level scheduled principal-and-interest payment, although taxes, insurance, mortgage insurance, escrow, and other housing costs can still change.
“Fixed rate” describes the interest-rate structure. It does not mean every mortgage charge is fixed or that the loan cannot be prepaid, refinanced, modified, or accelerated after default.
For a fully amortizing mortgage, the monthly principal-and-interest payment is calculated from the original balance, fixed rate, and number of payments:
where:
M is the monthly principal-and-interest payment;P is the original principal;r is the monthly interest rate; andn is the total number of monthly payments.The interest portion each month is the periodic rate multiplied by the outstanding balance. The remainder of the scheduled payment reduces principal.
Assume a $400,000, 30-year fixed-rate mortgage at 6.50%. The scheduled monthly principal-and-interest payment is approximately $2,528.27.
First-month interest is approximately:
First-month principal is therefore approximately:
As principal declines, monthly interest declines and more of the same scheduled payment goes to principal. If the loan remains outstanding for all 360 scheduled payments, total interest is approximately $510,177.95, excluding fees, late charges, prepayments, and other costs.
| Mortgage component | Fixed by the note rate? | Why it may change |
|---|---|---|
| Interest rate | Yes, for the contractual fixed term | Refinancing, modification, or contract enforcement can alter the arrangement |
| Scheduled principal and interest | Generally level on a fully amortizing loan | Recast, modification, curtailment treatment, or nonstandard structure |
| Property taxes | No | Government assessment and tax-rate changes |
| Homeowners insurance | No | Premium, coverage, property, and insurer changes |
| Mortgage insurance | No | Program terms, cancellation, termination, or premium rules |
| Escrow payment | No | Annual analysis and changed tax or insurance amounts |
| Association charges | No | Association budget and assessment decisions |
The total monthly housing payment can therefore increase even while the note rate remains fixed.
| Feature | Fixed-rate mortgage | Adjustable-rate mortgage |
|---|---|---|
| Note rate | Constant for contractual term | Can reset under index, margin, caps, and schedule |
| Principal-and-interest predictability | High on standard amortization | Lower after adjustment begins |
| Benefit from falling market rates | Usually requires refinancing | Rate may decline at reset, subject to terms |
| Exposure to rising market rates | Existing note rate protected | Borrower bears reset risk |
| Analysis focus | Rate, term, points, fees, prepayment | Initial rate, index, margin, caps, floor, reset path |
The lower initial rate is not always the lower-risk or lower-cost loan. Compare the full payment path and expected holding period.
Common U.S. fixed-rate mortgage terms include 15 and 30 years, but other terms exist. A shorter term generally requires a larger monthly payment and pays principal faster. A longer term generally lowers the required payment but can produce more lifetime interest.
The 15-Year vs. 30-Year Mortgage page isolates this term tradeoff with a worked comparison.
The same fixed-rate product may be offered at several rate-and-cost combinations:
One point equals 1% of the loan amount, but it does not reduce the rate by a universal amount. A lower rate with more points must be compared with a higher-rate, lower-cost alternative over a realistic holding period.
If market rates fall, the existing fixed note rate does not change automatically. Refinancing may lower the rate, but it creates a new transaction with underwriting, appraisal, title, closing costs, and a new amortization schedule.
A meaningful refinance comparison considers:
This article provides general financial education, not individualized mortgage, refinancing, legal, tax, accounting, or housing advice. Product availability, underwriting, disclosures, and consumer protections depend on the transaction and jurisdiction.