The loan amount is the home price minus your down payment. The monthly principal-and-interest payment is M = L × r ÷ (1 − (1 + r)−n), where L is the loan, r the monthly rate (annual rate ÷ 12) and n the number of monthly payments (years × 12). Property tax and insurance are divided by 12 and added on top. At a 0% rate the payment is simply the loan divided by n. Figures are estimates: lenders may also add mortgage insurance, HOA dues or escrow adjustments.
Example: a $350,000 home with 20% down is a $280,000 loan. At 6.5% over 30 years the principal and interest is about $1,770 a month, and you would pay roughly $357,000 in interest over the life of the loan.
The monthly payment is higher, but the interest is far lower. Change the term to 15 and compare the total interest figure.
20% avoids private mortgage insurance on most conventional loans, but many lenders accept 3 to 10% down. Enter a smaller percentage to see the effect on the payment, and remember to budget for mortgage insurance separately.
No. Closing costs (often 2 to 5% of the price) are paid up front and are not part of the monthly payment.
See also: loan calculator · compound interest calculator · percentage calculator