Are you the kind of person who doesn't like surprises? Then take a look at these calculators.

Amortization Calculator
See how fast your principal may decrease over the life of your loan.
Prepayment Analysis Calculator
Use this calculator to see how many months you can shave off your loan by prepaying on your principal, at a set monthly rate.
* results will change if you pay more or less than what is scheduled to be paid in any month.