Alright
Assumptions: house never appreciates (doesn't matter because both own same asset), 2.5% return 2000-2014 (actual return), 11% return 2015-2029 (actual return for 2015-2024 YTD). Average mortgage rates were 8% in 2000, I'm using 7.5% because I'm feeling generous and we both have good credit scores.
250k mortgage at 7.5%
15-year payment: $2,318
30-year payment: $1,748
Difference: $570
Both people have $2,318 to work with every month. 15 year mortgage guy obviously puts it all towards the mortgage beginning January 1, 2000 and pays it off December 31, 2014. From January 1, 2015 through December 31, 2023 he invests all $2,318 in the market.
The 30 year mortgage guy puts $1,748 towards his mortgage every month and the remaining $570 in the market for all 30 years.
On January 1, 2015
- 15 year mortgage guy has a paid off $250k house, $0 debt, and $0 in investments (+$250,000)
- 30 year mortgage guy has $61,433 in equity and $124,330 in investments (+$185,763)
On January 1, 2030
- 15 year mortgage guy still has paid off $250k house, $0 debt, and $1,053,970 in investments ($1,303,970)
- 30 year mortgage guy now has paid off $250k house as well, $0 debt, and $901,709 in investments ($1,151,709)
I think this breaks even somewhere around a 5.5% mortgage interest rates. Your strategy obviously works better when interest rates are low. You usually win out mathematically, perhaps even 90% of the time, but not always.