This decision should be based entirely on opportunity cost. For example, if you borrow $100 at 8% and the money can earn 10%, you are ahead of the game. The same simple analogy applies to deciding whether a mortgage should be paid off. Factor in income taxes as another variable and look at your opportunity cost. If you pay off a $100,000 mortgage at 8% you are basically saying, I do not think I could earn more than 8% on other investments.