What your monthly payment actually covers
The figure this calculator returns is your principal and interest (P&I) — the core of the loan repayment. Principal is the portion that reduces your outstanding balance; interest is the lender's charge for borrowing. In the early years of a 30-year loan, the overwhelming majority of each payment is interest, and only a sliver goes to principal. That ratio flips slowly over time, which is why building meaningful equity in the first few years is so gradual.
Your real-world housing payment is larger than P&I. Lenders typically collect property taxes and homeowners insurance in an escrow account, adding roughly $300–$800 per month depending on where you live. If your down payment is below 20%, private mortgage insurance (PMI) is added until you reach 20% equity. When you compare homes, always think in terms of the full PITI (principal, interest, taxes, insurance) payment, not just P&I.
How rate and term change the total cost
The interest rate has an outsized effect because it compounds monthly across hundreds of payments. On a $320,000 loan, moving from 7% to 6% lowers the monthly payment by roughly $210 and saves more than $75,000 in interest across 30 years. This is why locking a favorable rate — or refinancing when rates fall — matters so much.
The loan term is the other major lever. A 15-year mortgage carries a higher monthly payment but a lower rate and dramatically less total interest, because you are borrowing the money for half as long. A 30-year loan keeps monthly payments affordable but costs far more overall. Use the amortization schedule below to compare terms side by side and see how quickly the balance falls in each scenario.
Using the amortization schedule
Scroll to the amortization table to see every payment broken into principal, interest, and remaining balance. This view makes the power of extra principal payments obvious: an additional $150 per month applied directly to principal can shave years off a 30-year loan and eliminate a large chunk of interest, because every dollar of early principal reduction avoids all the future interest that dollar would have generated.