This is one of the most advanced mortgage calculators you will find. You can use it to see what your monthly payment will be and what you can potentially qualify for. It will show you the difference between a 15 year and a 30 year mortgage, what bi-weekly mortgage payments can do, and how 3-2-1 buy-down payments will look. It can also help you decide whether renting or buying will make more financial sense for you.
For the most accurate mortgage payment be sure to use the "advanced" mortgage payment calculator to include principal, interest, taxes, and insurance (PITI). Mortgage insurance can be added if you know the amount, typically applicable for FHA loans or certain conventional loans with less than 20% down. You can get approximate interest rates HERE, and yearly taxes will be displayed on property listings.
This calculator is a great guide, but loan qualification and interest rates will vary by person, be sure to consult with a trusted mortgage professional to discuss a pre-approval.