I think the idea is that you can plan on withdrawing 4% every year as well. The more flexible you are with your expenses, the more you can withdraw while ensuring you will have sufficient income throughout your retirement. I like the hybrid constant-percentage / constant-dollar withdrawal method where you keep 7.5 years of withdrawals in bonds and the rest in stocks. So a $1m portfolio produces $40k per year so 7.5x * $40k is $300k in bonds, and $700k in stocks. https://www.bogleheads.org/wiki/Withdrawal_methods#Combinati...