OK, we have a car. I would like to get it paid off sooner than deal calls for. I can pay additional on Principle, to make that happen....but haven't a clue as to how much extra will make a noticable difference in the number of payments and yet not break the bank. We owe about 3 more years on this car.

Is there a way to calculate or figure this out?

It is a simple interest loan, rather than a compound interest loan.