The monthly payment on a fixed-rate loan is P × r ÷ (1 − (1 + r)−n), where P is the amount borrowed, r is the monthly rate (annual rate ÷ 12) and n is the number of monthly payments (years × 12). At a 0% rate the payment is simply P ÷ n. Total cost is the payment times n, and total interest is total cost minus P.
This covers principal and interest only. Mortgages usually add property tax, insurance and sometimes mortgage insurance on top, and fees or a variable rate will change the real figure.
Try 15 years against 30 years: the monthly payment is higher, but the total interest is usually far lower, because you owe the principal for half as long.
Yes. Any fixed-rate loan with equal monthly payments uses the same formula: enter the amount, the annual rate and the term in years.
No, everything is calculated in your browser.
See also: Compound Interest Calculator · Percentage Calculator