Identify the amount borrowed
Start with the purchase price and subtract the down payment. A $300,000 home with a $60,000 down payment leaves a $240,000 loan before any financed closing costs. The loan amount, interest rate, and term determine the scheduled principal-and-interest payment.
Apply the monthly payment formula
For a fixed-rate, fully amortizing loan, payment = P × i / (1 − (1+i)^−n). P is principal, i is the annual interest rate divided by 12, and n is the number of monthly payments. The annual rate must be expressed as a decimal: 6% becomes 0.06 before dividing by 12. At zero interest, use P/n instead.
Add costs outside the loan
Property tax, home insurance, and homeowners association fees can make the housing payment larger than principal and interest alone. For example, $2,400 annual tax adds $200 per month. Another $1,200 annual insurance adds $100. These entered costs are estimates, and future bills may change.
Read the repayment table
With a typical fixed-rate amortizing mortgage, the balance declines over time. Interest uses the outstanding balance, so the portion of the payment reducing principal generally grows. FinMathly shows each monthly split. The model excludes PMI, maintenance, closing costs, and adjustable-rate changes. Ask the lender for its actual payment and disclosure schedule before relying on an estimate.
Further reading
CFPB: How paying down a mortgage works
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