Depends how much is left on the mortgage and what the interest rate is in my opinion. Yes, it has been hammered on this forum over and over that it is mathematically superior to invest into index funds rather than pay down your mortgage on a 30-year fixed rate mortgage, this is because for over the course of 30 years it is safe to assume a higher rate of return in the market than what your mortgage interest rate probably is. However, if you start talking about 1, 5, 10 years remaining on a mortgage, it becomes more likely that your mortgage interest rate will be higher than what you can return in the market during that much shorter period of time.