<prompt> Human: For example, say my monthly mortgage payment is 700. I pay 4.5 on the principal loan amount. If I contribute 800 one month, is that akin to investing the additional 100 at a guaranteed 4.5? My reasoning here is that I am no longer paying 4.5 interest on the 100. Am I thinking about this correctly?Besides the interest rate, this strategy is risk-free compared to investing. On the other hand, the principal of my investment really, the extra money towards the mortgage is illiquid until I sell the house.  <response>: Some other things to at least consider.1. Inflation. Not paying your mortgage off early assuming a fixed rate lets inflation benefit you because the real value of the interest payments decreases each year inflation occurs.2. Houses can decrease in value also. If the value of your home decreases precipitiously you could be financially better off by defaulting on your mortgage. 3. There are potential tax considerations on both sides of the equation. 