Hey Ben! Yes, our property taxes are so high-but at least we have no state income tax! Ah, I had a typo-the opportunity cost should be the surplus of mortgage payments if paid in 15 years, good catch! So true on the assumptions; everyone's portfolio and returns will be so different and whether you take out a 15 or 30 year mortgage will cause the #'s to fluctation (or if you try to pay the mortgage down earlier if you plan to retire early...that seems to be another popular choice in the FIRE community-no mortgage after retirement). Cheers!