I am not sure how this is usually calculated, but I noticed that every month one dollar less is added to my interest payment on my mortgage and one more is added to the principle payment. It seems odd that it’s so exact like that. But with the aid of the pull down feature in excel where it keeps subtracting or adding one to the number, I was able to project out how many years it would take me to pay off the loan. If I pay $200 extra a month it is paid off in 16 years. $250 extra gets is paid in 15 years, $300 in 14 years and $350 in 13 years or $400 extra each month will shorten it to just 12 years. What’s the savings in bank interest payments by paying $400 dollars extra each month? $28,000.00. (I’m not 100% sure I am calculating this correct, but I’d bet it’s close. ) That is about how much a down payment I paid. So you get that back if you pay early and pay often. Now I just have to figure out the budget so that I can afford that. Heh.