$300/month (at the beginning of the month) invested over 30 years, compounded annually at 6% = $198,290.40
If you kept that going for a full 50 years, the last 20 years of interest really starts to ramp up and gives you a final value of $1,084,402.22
If instead, you ONLY paid the mortgage for 30 years, then invest the full mortgage payment of $2,648 into the investment account for the next 20 years (a total of 50 years out. Same end point) you would have an investment account worth $1,215,042.49
So, even in your scenario it is still a loss to take a 50 year over the 30 year, and the 300$ difference is negligible. If $300 was the difference of someone being able to afford groceries or not for the month, then they should not have qualified for a $2,648/mo mortgage.
$300/month (at the beginning of the month) invested over 30 years, compounded annually at 6% = $198,290.40
If you kept that going for a full 50 years, the last 20 years of interest really starts to ramp up and gives you a final value of $1,084,402.22
If instead, you ONLY paid the mortgage for 30 years, then invest the full mortgage payment of $2,648 into the investment account for the next 20 years (a total of 50 years out. Same end point) you would have an investment account worth $1,215,042.49
So, even in your scenario it is still a loss to take a 50 year over the 30 year, and the 300$ difference is negligible. If $300 was the difference of someone being able to afford groceries or not for the month, then they should not have qualified for a $2,648/mo mortgage.