Shopping for a mortgage is not easy. While on the surface, a change to a new mortgage with a lower rate might seem like a good idea, being able to calculate the financial implications of this choice over the life of the mortgage is nontrivial. This Excel 2010 spreadsheet, which does include macros, provides the necessary functionality to perform the lifetime calculations. While this spreadsheet is offered with no guarantees or assurances of correctness, we used it to help us understand our options when it came time to refinance.
One of the interesting aspects of this spreadsheet is that it allows you to truly see the difference between 15 and 30 year loans. The difference in cost (all expressed in present dollars) is startling.