So my mortgage came with an Amortization chart, which is fine and all, but I want to be able to figure out how many years I'm cutting off of my mortgage (and how much interest I'm saving) by making two to three extra payments a year. Of course there are complications like the now permanent mortgage insurance and what not; but it seems to me that all of those are variables that can be accounted for and adjusted by a pretty simple calculator. Does anyone know of such a calculator I can find online?

I want to be able to input my mortgage amount, interest rate, estimated insurance and taxes, and mortgage insurance amounts, and change my monthly payment amounts to see how it affects my total years to pay off and total interest paid.