Updated 7/9/2015: The mortgage calculators are no longer active, as the RApache software has been discontinued.
Mortgage rates are low, considering historical rates for the last 50 years. It may be timely to consider a mortgage refinance. The image above links to a simple tool for exploring mortgage refinance, built using rapache and the yet-to-be-archived yarr package for R. Hence, there are now two mortgage-related calculators on this site:
While I believe both calculators to be accurate, I make no guarantees. You are welcome to browse the source code (single file, mixed R and HTML/CSS) for either calculator: MortCalc.yarr, RefiCalc.yarr.