My son showed me these calculators that figure it out for you....there's a separate calculator for either your credit card, mortgage, equity loan , car loan etc. etc. .....
The calculator lets you enter in what your paying
now and it will tell you how long and how much interest your going to end up paying.....
The neat thing is it lets you enter in another amount and it will tell you how much you will now
save in interest and how long it will take to pay it off....
The difference can be dramatic in just upping your payment just $20 and $50 dollars on some loans!...check it out, it's kind of fun!....
http://www.bankrate.com/brm/rate/calc_home.asp