Pay down or not pay down that is the question.

I use this method to determine whether paying down the mortgage or not.  Let's say the mortgage rate is 4% for 30 years.  The question is whether you can make more than 4% annual return on your 50K.  If the answer is YES, then don't pay down your mortgage.  Let's say your investment return is 6%, then 4% goes to the mortgage and you have 2% gain after that.  Actually, your mortgage rate could be lower if you have itemized your tax return and plus you are paying the mortgage with the depreciated dollar, so you effective mortgage rate could be around 3%.  At today's economy and market condition, I will not pay down the mortgage since I can make more in the market.  Hope this helps.  Good luck.