Mortgage interest can feel confusing because a fixed monthly payment does not mean interest and principal are split evenly. Early in the loan, the balance is larger, so more of the payment usually goes toward interest.
The basic idea
For a typical fixed-rate mortgage, the monthly principal and interest payment is calculated so the loan is paid off by the end of the term if every payment is made as scheduled. The interest portion depends on the current loan balance and the monthly interest rate.
Use the Mortgage Calculator to estimate principal and interest across different rates, loan amounts, and terms. Use the Amortization Calculator to preview how the payment split changes over time.
Why early payments include more interest
At the start of a mortgage, the balance is at its highest. Because interest is calculated from that balance, a larger share of the early payment goes toward interest. Later, as the balance falls, the interest portion shrinks and more of the payment reduces principal.
This changing split is called amortization. It is one reason extra principal payments can be more powerful earlier in the loan.
Principal and interest are not the full monthly payment
Your total mortgage payment may also include property taxes, homeowners insurance, mortgage insurance, and HOA dues. Those costs do not reduce the loan balance, but they do affect affordability.
When comparing homes or loan options, check the full payment, not only the principal and interest number.
How extra principal reduces future interest
When an extra payment is applied to principal, the loan balance falls faster. Future interest is then calculated on a smaller balance, which can reduce total interest and shorten the payoff timeline.
Use the Extra Mortgage Payment Calculator to test one-time payments, monthly extra payments, and payoff savings.
Helpful references
- CFPB: How mortgage lenders calculate monthly payments
- CFPB: Principal, interest, and total monthly mortgage payment
- CFPB: How paying down a mortgage works
Estimate interest cost
See how rate, term, and balance shape your payment.
Change the loan amount, term, interest rate, taxes, insurance, and extra payments to compare scenarios.