Loan amount and the payment formula
Home price minus down payment is the amount amortized. The monthly principal-and-interest payment is the standard fixed-rate formula. A 0% rate splits the balance evenly across the months. A 30-year term is 360 payments; a 15-year term is 180.
The default rate is the Freddie Mac Primary Mortgage Market Survey weekly national average stored on this site, not the rate a lender will offer in your ZIP. Credit, points, occupancy, and property type all move a real quote.