Fixed-Rate Mortgage Calculator Guide
A fixed-rate mortgage calculator estimates your monthly payment, total interest, and amortization schedule for a loan with a constant interest rate over its full term.
What Is a Fixed-Rate Mortgage Calculator?
A fixed-rate mortgage calculator computes the monthly payment required to repay a home loan where the interest rate remains unchanged for the entire loan duration. It uses the standard amortization formula: M = P[r(1+r)^n] / [(1+r)^n – 1], where P is the principal, r is the monthly interest rate, and n is the total number of payments.
Key Inputs
Loan Amount (Principal)
The total amount borrowed, typically the home purchase price minus your down payment. For example, a $500,000 home with a 20% down payment yields a $400,000 principal.
Interest Rate
The annual fixed interest rate quoted by your lender. This is divided by 12 to get the monthly rate used in calculations. A 6.5% annual rate becomes 0.5417% monthly.
Loan Term
The repayment period, most commonly 15 or 30 years. A 30-year term means 360 monthly payments. Shorter terms mean higher monthly payments but significantly less total interest paid.
How to Use the Calculator
Enter your loan amount, annual interest rate, and loan term. The calculator instantly shows your monthly payment (principal + interest), total interest paid over the life of the loan, and a full amortization schedule showing how each payment splits between principal and interest.
Understanding the Results
Monthly Payment Breakdown
Early payments are interest-heavy. On a $400,000 loan at 6.5% over 30 years, your first payment of $2,528 allocates $2,167 to interest and only $361 to principal. By year 20, the split reverses.
Total Cost of the Loan
The total amount you will pay over the full loan term, including all interest. For the example above, you would pay $910,178 total — $400,000 in principal and $510,178 in interest.
When to Use This Calculator
Use a fixed-rate mortgage calculator when comparing loan offers from different lenders, deciding between 15-year and 30-year terms, evaluating the impact of a larger down payment, or determining how much house you can afford based on your target monthly payment.
Related Guides
An adjustable-rate mortgage calculator estimates payments for loans where the interest rate changes periodically after an initial fixed period, helping you compare ARMs against fixed-rate options.
Mortgage Refinance Calculator GuideA mortgage refinance calculator determines whether replacing your current loan with a new one at different terms will save you money, factoring in closing costs and break-even timing.