There are several mortgage calculators available online for you to use, that can make it easy to determine your monthly payment. If you want to figure it out on your own you can use the following equation:
Monthly Interest (in decimal form)
Monthly Payment = Principal * -------------------------------------------
1 – (1+ Monthly Interest) - # of Months
If you are not a math whiz, I would suggest doing the math on a mortgage calculator online. It ca make the whole process a lot easier, and can allow you to change variables such as loan term and interest rate rather easily, and see what the difference may be.