I don't know if this is what you are looking for exactly, but there is a program MortgageCALC. It is awesome. It is freeware too, so at least it is worth trying out. You can look at it
Here on Handango.
Three quick points on it, so that you are not surprised when it happens. First is when you go into the program it takes a couple of seconds to load, and then it goes to a liability release statement and you have to hit I accept to get into the program. Secondly, when you go to a certain function (i.e. loan calculations) it also takes a couple of seconds to download the calculation tables. Finally, what I really like is that you can create your own calculations. And it has about every function Excel has, so you don't have to skimp. I quickly created a tip and sales tax calculator just to see how easy it was. I plan on creating some other functions I use day in and day out in my job just to help out.
Also this calculator does so much more than just mortgages, it has a conversion utility already installed as well along with about 12 other functions already installed, and it has graphs for each as well.
I would give this 5 Stars, and recommend it for anybody. It doesn't replace your basic calculator, but it does so much finance wise. Perfect for longterm investments including cars, homes, other real estate, and loans.
Check it out and I hope you like it as much as I do. And for no cost this program is unbelievable, it easily could sell for $30 for more.