New house with 30yr @ 4.375% mortgage that can be refinanced to a 15yr @ 3.1%. $190k owed on mortgage. Assuming you have $2k per month of available funds for paying your mortgage and investing, what would you do? To make things even more tricky, if the house could be payed off in full with savings and selling some taxable investments, does this change anything?
I'm looking at this in terms of a 15 year horizon (ie. conservative investment gains at 15yrs minus interest paid on the loan minus any principal left on the mortgage at 15yrs.
My calculations show the following:
- Paying the 30yr mortgage at the normal rate leaves you with $325k and it's not paid off for 30 years

- Paying down the 30yr mortgage with either a single large lump sum at the beginning or several hundred dollars every month throughout the mortgage leaves you with $350-380k. A little better plus the house gets paid off in 10-20 years depending on how aggressive you go.
- Refinancing to a 15yr at either $190k, $150k, or $100k all leave you with around $450k after 15 years.
- Paying the house off outright and investing $2000 a month for 15 years leaves you with $730k

Assumptions: I used the 25th percentile Monte Carlo (60% stock/40% bonds) for investment gains. In reality, the bonds would go into tax advantaged accounts and the taxable investing will be 100% TSM. I did not take into account any tax deductions that holding onto the mortgage gives you.
Am I missing something? Do you really come out so far ahead by paying the mortgage off even in such a low interest rate environment?