<prompt> Human: Lets say I have zero debt, and I am about to take on a 30 year 400K mortgage at 4.5 interest 20 downpayment. I am very sure 95 that over 30 years if I invest my own money, after taxes, I will average at least a 4.75 return.Ignoring all the perks of things like Mortgage Interest Deduction and the value of extra liquid cash -- does it ever make sense to apply that money to paying down principal rather than investing it myself?  <response>: In your scenario, Id have to ask at what point you think security is worth more than speculation. By paying the home mortgage, you guarantee 4.5 savings. Or, you could gamble to get 4.75 return. Is that uncertainty of your future returns worth .25? Of course, if your rate is 4 and you believe you would get 6, 7, or 8, Id lean more towards investing rather than paying down the mortgage. Sidenote: It also depends on if you want to tie your assets up in a house or if youd rather have them available to you should the need arise 