Check out a great mortgage app at www.simplenexus.com or call 855-684-2777 ext 203 and they will give you a 1 month free code!
Android has one called Karls Mortgage Calculator and its half decent actually. Nothing beats a real handheld mortgage calculator thought. (Not everything needs to be on a smartphone) :-)
Dont forget to account for closing costs and fees financed when you calculate your payment. Add a few grand to the loan amount for themost realistic calculation. Most mortgage apps wont add the fees points and costs.